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On a recent November morning, more than 20,000 western monarch butterflies clustered in a grove of eucalyptus, coating the swaying trees like orange lace. Each year up to 30% of the butterfly’s population meets here in Pismo Beach, California, as the insects migrate thousands of miles west for the winter.
Just a year ago, this vibrant spectacle had all but disappeared. The monarch population has plummeted in recent years, as the vibrant invertebrates struggled to adapt to habitat loss, climate crisis, and harmful pesticide-use across their western range.
Last year less than 200 arrived at this site in 2020 – the lowest number ever recorded – and less than 2,000 were counted across the California coast.
But ahead of the official annual count that takes place around Thanksgiving, early tallies show monarchs may be thriving once again across California. The rise has sparked joy and relief, but the researchers, state park officials, and advocates say that doesn’t mean the species is safe.
Up to 30% of the western monarch butterfly population converges on Pismo Beach each winter. Photograph: Gabrielle Canon/The Guardian
“The takeaway is that the migration isn’t gone, which some people really feared last year,” says Emma Pelton, the senior conservation biologist for the Xerces Society, an organization dedicated to protecting pollinators and other invertebrates. Between 4 million and 10 million butterflies once graced the California coasts before dropping to just over a million at the end of the 1990s. In the decades that followed, the population plateaued at about 200,000.
Then, in 2017, the numbers crashed to fewer than 30,000 butterflies at the annual counts. Monarchs are resilient and adaptive but they continue to face challenges. This year’s uptick is small when put in perspective with past population levels, but “the good news is that it is not too late”, Pelton adds.
A remarkable migration
There’s still a fair amount of mystery surrounding the western monarchs and their incredible annual migration. Each year, they follow a celestial compass and head west from the Rocky Mountains to the coast. Remarkably, each generation of butterflies often returns the same groves along the coast each year, sometimes even a particular tree, without ever having been there before.
Generally, they arrive in California around November and disembark in the spring, heading east as the weather warms. A separate population of monarchs spends the winter in Mexico, coming from Canada and the eastern United States.
Stephanie Little, a scientist with California state parks, counts butterflies in Pismo Beach. Photograph: Gabrielle Canon/The Guardian
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Their dedication to routine makes them easier to count each year. But the process isn’t exactly simple, especially when the numbers are low and they are harder to spot. In the Pismo Beach grove, which usually hosts the largest gathering, there are three state parks officials tasked with tallying them before the Thanksgiving count that relies on help from volunteers.
Armed with binoculars, butterfly counters estimate the numbers based on clusters that can be seen in the branches, roughly 50ft (15 meters) from the ground. California state parks has partnered with advocacy organizations to produce a welcoming environment for them. That means planting more of the non-native eucalyptus trees, which the butterflies love to roost in.
The reasons behind this sharp increase remain a mystery. Monarchs that live in the west tend to have three or four generations each year, each with a different role to play in the migration that can span thousands of miles, and there are opportunities at each stage for big shifts.
Monarch butterflies gather in the branches of a eucalyptus tree, roughly 50ft from the ground. Photograph: Gabrielle Canon/The Guardian
But what’s driving their precipitous decline is clear. Their historic habitats in grassland ecosystems across the US are being destroyed. Commercial agriculture is eating away at their range which is increasingly laced with deadly pesticides. And, susceptible to both fluctuations and extremes in temperatures, monarchs are vulnerable to climate change. That’s partly why they are considered a so-called “indicator species” revealing the devastating toll taken on other insects and ecosystems.
“The butterflies are just very adaptable and strong,” David James, an entomologist at Washington State University who has spent decades studying the species says. “But they are giving us a warning too – and we need to take heed of that,” he adds. “Their decline is going to affect other organisms.”
‘There’s still time to act’
The butterflies have also felt the impact of extreme heat, fires, and drought, as well as the severe winter storms on the California coast where they spend the winter. “Some of those storms have ripped the trees out and thrown butterflies to the ground,” James says.
But he also believes last year’s extremely low numbers may have been the result of dispersion, not necessarily death.
“When we only had 2,000 overwintering at the traditional sites, at the same time there were many reports inland in San Francisco and the LA area of monarch butterflies reproducing in people’s backyards and parks and gardens throughout the winter,” he says, noting that this spread makes them tricky to count.
But even if last year’s low numbers can be attributed to behavior changes, that’s still a sign climate crisis is causing problems. “They are indicating to us that things are going wrong,” James says.
Visitors look for butterflies at the Pismo Beach Butterfly Grove. Photograph: Gabrielle Canon/The Guardian
Individuals can make a difference by planting native nectar plants, including the milkweed that monarchs lay their eggs on and limiting the use of pesticides. Members of the public can also volunteer to monitor monarchs across the west. And, according to Xerces’ Emma Pelton, the promising numbers show that small changes can have a big impact.
“The main message to me is that there’s hope,” she says, noting the way monarchs have inspired the public to reimagine how they see insects and the role that everyone can play in their conservation. “The insect apocalypse narrative and the very real biodiversity crises that we are facing, those can feel really dark” she says. “But the issue is not intractable and we can make a difference. There is still time to act.”
IMAGE: ENTOMOLOGIST AT WORK IN THE HYMENOPTERA COLLECTION, HOUSED AT THE INSTITUTE OF SYSTEMATICS AND EVOLUTION OF ANIMALS, POLISH ACADEMY OF SCIENCES IN CRACOW.view more CREDIT: KAROLINA FOK (WIKIMEDIA COMMONS LINK: HTTPS://COMMONS.WIKIMEDIA.ORG/WIKI/FILE:ENTOMOLOGIST_AT_WORK_IN_THE_HYMENOPTERA_COLLECTION._INSTITUTE_OF_SYSTEMATICS_AND_EVOLUTION_OF_ANIMALS_POLISH_ACADEMY_OF_SCIENCES_IN_CRACOV.JPG)
For the past five months, the European Commission-funded project ‘European Red List’ of Taxonomists has been reaching out to insect taxonomists to invite them to register at the Red List of Taxonomists portal.
Behind the project are the organisation uniting the most important and largest European natural science collections (CETAF), the world’s authority on assessing the risk of extinction of organisms: the International Union for Conservation of Nature (IUCN) and the scientific publisher with a long history in the biodiversity and ecology fields Pensoft.
“It’s never been as clear that the sustainability of our ecosystems and economies are tightly connected to how healthy our pollinators and other insects within the intricate web of life are. So, it is obvious that securing the constant flow of scientific knowledge shall be of utmost importance to everybody,” say the project partners.
“At the end of the day, it’s the experts who identify insects and investigate their abundance and diversity that are best equipped to inform the community – including the key decision-makers – about things like what native species are in urgent need of protection, which ones have recently started to diminish, and how to spot invasives well known for their harm on local biodiversity. The major problem, however, is that these experts are rapidly declining themselves.”
Having filled in their details, such as country of residence and activity, institutional affiliation, seniority and insect group of interest, over 1,200 participants provided valuable data necessary to estimate the actual number, location and profile of the insect taxonomists based or working in Europe. The final report – to be released in early 2022 – will also present past and future trends of expertise within the continent and across insect taxa. A comprehensive list of recommendations will shed light on where and what support is needed to prevent the ‘extinction’ of experts and their invaluable contributions to evidence-based conservation efforts.
In particular, the final recommendations are to highlight all key measures and tools expected to bridge the identified gaps at both national and pan-European level, including the use of relevant funding programmes. The report will also include an estimate of the associated efforts and costs.
Follow and join the conversation on Twitter using the #RedListTaxonomists hashtag.
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Additional information:
CETAF is the European organization of Natural History Museums, Botanic Gardens and Research Centers with their associated natural science collections comprising 71 of the largest taxonomic institutions from 22 European countries (18 EU, 1 EEA and 3 non-EU), gathering expertise of more than 5,000 researchers. Their collections contain a wide range of specimens including animals, plants, fungi and rocks, and genetic resources which are used for scientific research and exhibitions. CETAF aims to promote training, research collaborations and understanding in taxonomy and systematic biology as well as to facilitate access to our natural heritage by sharing the information derived from the collections. Follow CETAF on Twitter, Facebook and LinkedIn.
IUCN (the International Union for Conservation of Nature) is a membership Union composed of both government and civil society organisations. It harnesses the experience, resources and reach of its more than 1,400 Member organisations and the input of more than 17,000 experts. This diversity and vast expertise makes IUCN the global authority on the status of the natural world and the measures needed to safeguard it. Follow IUCN on Twitter, Facebook and LinkedIn.
Pensoft is an independent academic publishing company and technology provider, well known worldwide for its novel cutting-edge publishing tools, workflows and methods for text and data publishing of journals, books and conference materials. Through its Research and Technical Development department, the company is involved in various research and technology projects. Founded in 1992 “by scientists, for scientists” and initially focusing on book publishing, Pensoft is now a leading publisher of innovative open access journals in taxonomy and biodiversity science. Follow Pensoft on Twitter, Facebook and LinkedIn.
The Detail: The sky-high cost of living in New Zealand
The Detail explores what makes our food so pricey when we produce enough to feed 40 million people.
There are also more than 350 restaurants, cafés and fast-food outlets involved – and the restaurant and ready-to-eat-food prices increased 4.6 per cent. Further, 30 per cent of the food budget is now spent on convenience, despite lockdown and the perceived focus on home cooking.
For the farmer, this means that more of what consumers spend is on processing and preparation, rather than on the basic food they have produced.
ALDEN WILLIAMS/STUFFFood prices rose 4 per cent in the year ending September 2021 (file photo).
The New Zealand Institute of Economic Research analysed the farm share of retail prices in 2019. Approximately 31 per cent of every dollar spent on meat returned to the farm, 19 per cent of dairy dollars, 22 per cent of grain dollars, 10 per cent of fruit, 16 per cent of vegetables and 2 per cent of the egg dollar.
Not much, really.
And farmers are consumers – so they have been hit by inflation like every other business. In the last quarter, prices paid by farmers have increased 5.9 per cent. Prices received were certainly up 4 per cent, but that hasn’t covered the increase in costs of fertiliser, fuel, electricity and wages.
Even more of a shock might be that what is being experienced in New Zealand in terms of increased food prices is nothing in comparison with that being experienced in the world. The FAO food price index has increased 32.8 per cent from September 2020 – food prices globally have increased by a third in a year.
STUFFDr Jacqueline Rowarth: “Ever-cheaper food … is likely to be a thing of the past as farmers try to manage improved productivity (more food with reduced inputs) within the uncertainties of a changing environment.”
Uncertainty in harvest due to Covid-19, fire, drought and flood, as well as demand, have combined to stimulate inflation not seen since 2011. Food accessibility (available and affordable) is an issue globally.
Ever-cheaper food, though an expectation in developed countries, is likely to be a thing of the past as farmers try to manage improved productivity (more food with reduced inputs) within the uncertainties of a changing environment – due to both the climate and regulation.
On April 29, the Sri Lankan Cabinet approved a ban on importation of chemical fertilisers and other agrochemicals in a bid to become the first country to practise organic-only agriculture. Less than six months later and the government has backed down. Yields and quality of tea crashed.
Despite well-meaning belief, there was insufficient organic fertiliser available for the tea plantations. And with lower yields and quality, tea prices increased, meaning local tea drinkers were as unhappy as the growers.
JAROMÃR KAVAN/UNSPLASH Sri Lanka wanted to be the first country to practise organic-only agriculture. Less than six months later and the government backed down after yields and quality of tea crashed.
In the European Union, Farm Europe (a think tank) has calculated that the new farm to fork strategy will have significant impact on food supply, and hence food prices. The strategy recommends reducing the use of chemical pesticides by 50 per cent and fertilisers by 20 per cent, setting aside of at least 10 per cent of agricultural area under high-diversity landscape features and putting at least 25 per cent under organic farming.
The estimated result will be a reduction in food supply by 10 to 15 per cent in the key sectors of cereals, oilseeds, beef, dairy cows; over 15 per cent in pork and poultry; and over 5 per cent in vegetables and permanent crops. There will be an increase in prices by 17 per cent and little to no increase in biodiversity or ecological benefits.
Increasingly, research is showing that our best chance of preserving biodiversity and achieving ecological benefits is to ensure productivity gains on existing agricultural area. This will avoid needing more area to compensate – deforestation being the most obvious detrimental effect. The big differences in biodiversity are between natural and managed ecosystems, not within different types of management (organic versus conventional, for instance).Get the latest small business updates, straight to your inboxSubscribe for free
While the wealthy countries develop new technologies to assist the challenge of meeting the nutritional needs of an ever-increasing global population from current agricultural land, work is vital with the less developed countries to help them achieve higher yields – to overcome what is known as the yield gap.
Better soil management, improved genetics and matching inputs with plant and animal needs (including health and welfare) is key. So is harvesting, processing, storage and distribution to reduce waste.
New Zealand farmers already hold global records in yield (grain) and low GHG (meat and milk). They are also leaders in precision agriculture. Food here is produced without the subsidies common in other countries. Removal of technological tools will increase prices to the consumer as already calculated for the EU.
For good policy to be developed, all the different consequences need evaluation. Research is showing the way.
– Dr Jacqueline Rowarth, Adjunct Professor Lincoln University, is a farmer-elected director of DairyNZ and Ravensdown. The analysis and conclusions above are her own. Contact her at jsrowarth@gmail.com.
Henrik Barmentlo at work at the Living Lab, accompanied by Professor Martina Vijver. Credit: Edwin Giesbers
The widely used pesticide thiacloprid can cause a large-scale decline in freshwater insects. This was discovered by researchers from the Living Lab in Leiden. For three months they counted the flying insects in the 36 ditches of the lab. Their research appeared in PNAS.
In the ditches of the Living Lab, Henrik Barmentlo and his colleagues exposed freshwater insects to different concentrations of thiacloprid. This substance belongs to the neonicotinoids, the world’s most widely used group of insecticides. “We used realistic concentrations,” says Barmentlo. They correspond to concentrations we actually measure in the surface water.
Dramatic decline in all species
That neonicotinoids can be harmful to many insects had already been proven. But there was no conclusive evidence that these insecticides are at least partly responsible for the large-scale insect decline.
Therefore, in a unique experiment, the researchers caught no less than 55,574 insects that flew out of the lab’s 36 thiacloprid-contaminated ditches over a period of three months. Afterwards, they identified all specimens. They compared the results with nine control ditches, without added thiacloprid. Barmentlo: “We saw dramatic declines in all the species groups studied, such as dragonflies, beetles and sedges. Both in absolute numbers and in total biomass. In the most extreme scenario, the diversity of the most species-rich group, the dance flies, even dropped to a single species.”
Consequences for the whole ecosystem
And that while all these insects have an important role in their ecosystem. For example, they serve as food for many insect-eating bird species. Previously, other researchers had already discovered that these bird species occur in lower numbers when there are more neonicotinoids in the water. Barmentlo: “So it is quite possible that these bird species suffer from a lack of insects, or in other words: food.”
Barmentlo calls the results alarming. “Given the urgency of the large-scale decline in insects, we think the mass use of these insecticides should be reconsidered. In the EU, the use of thiacloprid was banned last year, but not yet in other parts of the world. In order to protect freshwater insects and all the life that depends on them, we must stop using these neonicotinoides as soon as possible.”
Environmental damage from insecticide overuse is a major concern, particularly for conservation of “good” insects such as pollinators that ensure stable production of food crops like fruits and vegetables. However, insecticides are also necessary for farmers to manage “bad” insects (i.e., pests), and thus, a more holistic view of crop management needs to account for the proper balance between the beneficial and detrimental aspects of pesticides. Here, we used multiyear field experiments with a paired corn–watermelon cropping system to show that insecticide use can be dramatically reduced (by ∼95%) while maintaining or even increasing yields through the conservation of wild bees as crop pollinators. These data demonstrate that food production and ecosystem sustainability are not necessarily conflicting goals.
Abstract
Pest management practices in modern industrial agriculture have increasingly relied on insurance-based insecticides such as seed treatments that are poorly correlated with pest density or crop damage. This approach, combined with high invertebrate toxicity for newer products like neonicotinoids, makes it challenging to conserve beneficial insects and the services that they provide. We used a 4-y experiment using commercial-scale fields replicated across multiple sites in the midwestern United States to evaluate the consequences of adopting integrated pest management (IPM) using pest thresholds compared with standard conventional management (CM). To do so, we employed a systems approach that integrated coproduction of a regionally dominant row crop (corn) with a pollinator-dependent specialty crop (watermelon). Pest populations, pollination rates, crop yields, and system profitability were measured. Despite higher pest densities and/or damage in both crops, IPM-managed pests rarely reached economic thresholds, resulting in 95% lower insecticide use (97 versus 4 treatments in CM and IPM, respectively, across all sites, crops, and years). In IPM corn, the absence of a neonicotinoid seed treatment had no impact on yields, whereas IPM watermelon experienced a 129% increase in flower visitation rate by pollinators, resulting in 26% higher yields. The pollinator-enhancement effect under IPM management was mediated entirely by wild bees; foraging by managed honey bees was unaffected by treatments and, overall, did not correlate with crop yield. This proof-of-concept experiment mimicking on-farm practices illustrates that cropping systems in major agricultural commodities can be redesigned via IPM to exploit ecosystem services without compromising, and in some cases increasing, yields.
Integrated pest management (IPM) is a central organizing principle to guide pesticide use. At its core, IPM is designed to optimize pesticide inputs, preventing overuse via practices such as scouting with applications dictated by a range of parameters, including economic thresholds, heat unit accumulations, and historical data (i.e., a use-as-needed approach). Although IPM has been a mainstay in agriculture for >50 y (1), technological and philosophical changes in farming practices over recent decades have made this well-accepted and effective approach to pest management far more difficult to implement in practice (2, 3). A contributing factor to this trend is the introduction and widespread adoption of prophylactic neonicotinoid seed treatments (NSTs) on staple crops such as corn, soybean, cotton, and wheat (hereafter “row crops”). Unlike some transgenic crops (i.e., Bt hybrids), NSTs were not developed in response to new or recurring pest outbreaks; in fact, pest populations remain at historic lows in many US crops (4, 5). As a result, studies have struggled to document a clear agronomic or economic benefit from using NSTs in the United States and Canada (6⇓⇓⇓⇓⇓⇓–13), likely due to the sporadic occurrence of the pests they are purported to control. In a recent analysis, <5% of corn fields in Quebec experienced a measurable benefit from the use of NSTs (14). Yet, >90% of corn and >50% of soybean and cotton seed is coated with a neonicotinoid in the United States (15, 16). NSTs could, in theory, conform to an IPM framework if proactive, insurance-based pest management is justified by persistent pest pressures (17); however, the existing data largely do not support this view, especially in northern temperate regions (e.g., the US “Corn Belt”).
The lack of yield benefit from NSTs is also concerning due to accumulating evidence of nontarget effects from their overuse (18⇓–20). When evaluated, <5% of NSTs were absorbed by the crop (21), with the remaining active ingredient lost to the greater ecosystem (10, 22), where it can persist for years in groundwater (23, 24) and soil (25, 26). The pervasive use of NSTs has led to contamination of waterways near crop fields (27), noncrop wild plants (28⇓–30), pollen and nectar in honey bee colonies (31⇓–33), and even human hair (34) and drinking water (35).
Although a wide diversity of nontarget animals is vulnerable to neonicotinoid exposure, pollinating insects have been the most well-studied group, in no small part because of global declines in bee populations (36, 37). The insecticidal toxic load for honey bees has dramatically increased over the past 20 to 30 y despite declining application volume (38, 39). This change was most evident in the US Heartland, with a 121-fold increase in oral toxicity, an effect attributed almost completely to corn and soybean NSTs. These patterns suggest that neonicotinoid inputs in row crops have the potential to profoundly affect pollinator health across landscapes, with potential reverberations in noncorn/soybean habitats.
Most fruits, vegetables, and tree nuts (hereafter “specialty crops”) are at least partially—and, in some cases, entirely—reliant on insect pollinators for yield (40⇓–42). Consequently, NST-mediated impacts have the potential to threaten food production. However, the crops driving neonicotinoid exposure are not the same ones that depend on bees for their services. Corn, soybean, and cotton account for >80% of neonicotinoid use (15), but both soybean and cotton are primarily considered self-pollinating [despite some recent evidence for yield benefits with bee visitation (43, 44)], and corn is wind-pollinated. Although bees are known to visit these crops for nectar and/or pollen, insect pollinators are not critical to their production. Row crops are cultivated over a large fraction of arable land in the United States [9.8% of the continental United States is dedicated to corn, soybean, and cotton (45)], and specialty crop fields in this region are often adjacent to at least one of these row crops; therefore, we may expect carryover effects of NSTs on specialty crop pollination. For example, NST-infused dust from corn planting moves hundreds of meters beyond the field border (10, 32, 46), resulting in honey bee mortality (summarized in ref. 47). Thus, the relatively smaller areas devoted to specialty crops may invariably experience extrafield exposure from nearby row crops. Similarly, specialty and row crops are common rotation partners, resulting in neonicotinoid soil residues that impact ground-nesting bees (48⇓–50). These spatial and temporal avenues generate several possible exposure routes. A simulation model (46) using field-derived values predicted that NSTs from corn planting in late spring erode honey bee population size enough to reduce capacity for blueberry and cranberry pollination later that summer, resulting in the potential for economic losses to neighboring berry growers. A similar outcome was demonstrated when modeling almond pollination potential for honey bee colonies that reside in the corn-dominated Northern Great Plains for much of the year (51).
In the work described here, we empirically test the hypothesis that IPM implementation, consisting of pest thresholds and removal of NSTs, dramatically reduces insecticide use and improves pollinator function without sacrificing crop yields. To do so, we used a multiyear, multisite field study, conducted in a dual cropping system representative of agriculture in the midwestern United States, and other parts of the world, consisting of a smaller acreage specialty crop paired with (i.e., adjacent to and grown in rotation with) a larger acreage row crop. We compared the effects of IPM versus conventional insecticide practices across several key metrics: insect pest abundance and damage, pollination, and yield. This design is unique in integrating field measurements of all factors across years, locations, and cropping systems. We paired field corn and seedless watermelon—a functionally dioecious crop that requires bees to move pollen between plants for fruit production. The experiment was conducted over 4 y (2017 to 2020) across five sites in Indiana, a state that is typically ranked in the top five nationally for both corn and watermelon production (52). In the conventional management (CM) system, we applied industry-standard practices used by growers in the region, characterized by NSTs on corn and preventative, calendar-based insecticides on watermelon. In the IPM system, we used NST-free corn seed with watermelon inputs determined by population thresholds established for arthropod pests. We predicted that the IPM system would have both higher pest densities (while remaining below economic thresholds) and pollinator visitation rates, resulting in equivalent (corn) or higher (watermelon) crop yield and increased farm profitability. This field experiment provides a comprehensive reassessment of IPM principles for both modern row crop and specialty crop pest management in the highly productive and intensively managed agricultural region of the midwestern United States.
Results
IPM Systems Experienced Infrequent Pest Outbreaks, Requiring Few Insecticide Inputs.
Neonicotinoid seed treatments target early-season pests; however, early-season corn damage was unaffected by NSTs with corn plant stand similar (P = 0.867) between IPM (11,040 ± 145 plants ⋅ ha−1) and CM (11,052 ± 106 plants ⋅ ha−1) fields (SI Appendix, Fig. S3; refer to SI Appendix, Table S6Afor full statistical model for this and subsequent pest metrics). Similarly, during the first 3 y of the study, <1% of sampled plants showed any direct evidence of feeding by western corn rootworm Diabrotica virgifera virgifera LeConte—the primary insect pest of corn in this region—across both treatments (overall damage rating: 0.001 ± 0.000 nodes). In the fourth and final year (2020), damage was more prevalent, with 33% of IPM corn roots showing evidence of rootworm feeding. This pattern resulted in a significant treatment × year interaction (P = 0.006), with pairwise comparisons showing that IPM fields in 2020 had higher damage ratings than all other treatment × year combinations (SI Appendix, Fig. S4). Despite this statistical increase in pest pressure in the IPM treatment over time, the magnitude of the effect was low (2020 IPM damage rating (on a 0-to-3 scale): 0.17 ± 0.07 nodes).
Watermelon in the CM treatment received insecticide sprays on a predetermined schedule that did not depend on scouting. These calendar applications maintained populations of the primary insect pest—striped cucumber beetle (SCB) Acalymma vittatum (F.)—well below the published economic threshold of five beetles per plant (Fig. 1A; seasonal mean SCBs per plant = 0.11 ± 0.05). In IPM fields, SCBs also rarely reached their economic threshold (Fig. 1B; seasonal mean SCBs per plant = 1.18 ± 0.34). Over the 3-y experiment, only four total IPM insecticide sprays (2018: 1; 2019: 1; and 2020; 2) were required across all five sites combined (i.e., four applications in 15 site-year growing seasons). In contrast, 77 insecticide applications were made in the CM treatment over the same period across all sites. In the IPM treatment, a single spray per field was sufficient to keep populations below economic thresholds for the remainder of the season; however, in most site-years, even a single spray was unnecessary. Appearance of secondary pests—primarily aphids and spider mites—occurred under both management systems (CM = 6, IPM = 4), but, interestingly, these populations only warranted additional pesticide applications (n = 2) in the CM plots (SI Appendix, Table S5). All other observed secondary pests did not spread to neighboring plants and were likely controlled by abiotic factors (heavy rain) or natural enemies, which were confirmed by the presence of parasitized aphids or coccinellid larvae/adults on flagged plants known to be previously infested.
SCBs were higher in IPM watermelon fields, but infrequently reached levels associated with economic loss. Watermelon fields within both a CM (A) and IPM (B) system were scouted weekly, and each point represents a 15-plant average of SCBs from seedling transplant until fruit harvest. Red lines in each graph indicate the five-beetle/plant economic threshold, while circles (2018), squares (2019), and triangles (2020) differentiate experiment years. In IPM fields, in each instance in which beetle levels reached the economic threshold, insecticide was applied <2 d following the survey.
Pesticide Residues Were Higher in Conventionally Managed Systems.
Neonicotinoids applied to both crops in the CM system were routinely found in sampled plant tissues and soil; 99% (n = 335) of all samples collected had residues of at least one neonicotinoid compared to only 65% (n = 221) of IPM samples.
Neonicotinoids in the pollen of both crops were higher in the CM than IPM treatment. Watermelon pollen had consistently higher concentrations of imidacloprid in CM (median: 6.17 ng/g) compared to IPM (median: < limit of detection [LOD]) flowers (Table 1); however, residues in CM fields decreased over time, with highest values in early-blooming flowers (SI Appendix, Table S8). Both clothianidin (CM: 49%, IPM: 5%) and thiamethoxam (CM/IPM median: < LOD) were infrequently detected at low levels in watermelon flowers. Corn pollen, on the other hand, rarely contained imidacloprid residues (CM: 50%, IPM: 10%), but CM corn pollen contained higher levels of both clothianidin (93% detection, median: 1.91 ng/g) and thiamethoxam (100% detection, median: 2.01 ng/g) than IPM corn pollen, which only contained detectable amounts of clothianidin and thiamethoxam in 20% and 10% of all samples, respectively (Table 2). This low-level contamination is likely attributable to uptake of carryover NSTs from previous cropping seasons before the experiment began or from adjacent fields.
Neonicotinoids were more frequently detected in corn pollen from fields under conventional management
Neonicotinoid residues were also higher in soil and leaf samples within the CM management system, depending on sample date. Refer to SI Appendix, Tables S7–S9 for pesticide summary data across all sample types and years. Nonneonicotinoid pesticides applied to the system—fungicides and the pyrethroid lambda-cyhalothrin—were also detectable but at varying levels (SI Appendix, Table S10). In general, fungicide detection was roughly equivalent across CM and IPM fields, whereas lambda-cyhalothrin was more frequently detected in watermelon leaves and pollen in CM fields (but overall detection rates were relatively low; <20% of samples).
IPM Enhanced Watermelon Pollination.
The pollinator community composition was broadly similar across treatments, with the most commonly observed taxa being honey bees, Apis mellifera (CM = 35%, IPM = 13%), Melissodes sp. (CM = 22%, IPM = 25%), and Lasioglossum + Halictus sp. (CM = 26%, IPM = 37%) (refer to SI Appendix, Fig. S5 and Table S11 for a complete description across taxa). Overall abundance of pollinators visiting flowers was 99% greater in IPM (0.64 ± 0.05 pollinators ⋅ min−1) than CM (0.32 ± 0.02 pollinators ⋅ min−1) fields (refer to SI Appendix, Table S6Bfor full statistical model for this and subsequent pollination metrics). Notably, this pattern was driven entirely by wild bees. When treatment effects were tested for managed and wild species as separate groups, there was no impact on honey bee visitation (P = 0.202), but wild bee visitation was lower (P < 0.001) in CM fields.
Number of flowers visited per minute was 129% greater in IPM (1.25 ± 0.11 visits ⋅ min−1) than in CM (0.55 ± 0.05 visits ⋅ min−1) fields (Fig. 2A). Also, transition visits (observed trips from male to female flower) were 305% higher in IPM (0.18 ± 0.02 transition visits ⋅ min−1) than CM (0.05 ± 0.01 transition visits ⋅ min−1) fields (Fig. 2B).
The rate of visits to watermelon flowers (A) and transition visits from a male to female flower (B) were both significantly higher in IPM fields. Each point within a cluster (n = 5) represents all observations from a single site during that field season (225 observation minutes). Whiskers within the plot show the mean ± SEM of all sites within each cluster.
NSTs Did Not Affect Corn Yield.
There was no statistical difference (P = 0.097) in corn yields between management systems, but there was a trend for higher yield in IPM (10,602 ± 479 kg/ha) compared to CM (9,471 ± 694 kg/ha) fields (Fig. 3A; refer to SI Appendix, Table S6Cfor full statistical model for this and subsequent yield metrics). Similarly, we conducted a more targeted small-plot trial in 2019 with higher replication and better control of local environmental factors. This follow-up experiment also showed no difference (F1,51 = 0.47, P = 0.501) between +NST (12,688 ± 269 kg/ha) and −NST (12,511 ± 311 kg/ha) corn yields (SI Appendix, Fig. S6).
Corn yield was unaffected by CM system (A), but watermelon yield was significantly higher when grown under an IPM system (B). Each point within a cluster (n = 5) represents the yield from a site during that field season. Whiskers within the plot show the mean ± SEM of all sites within each cluster. Corn and watermelon icons from BioRender.
IPM Watermelons Produced Higher Yields by Preserving Wild Bees.
Watermelon yield was 25.7% higher in IPM (9.91 ± 0.84 kg/m2) than in CM (7.88 ± 0.63 kg/m2) fields (Fig. 3B). The significant difference in overall yield between treatments (P = 0.002) was driven by the reduced number of watermelons harvested in CM (59.07 ± 4.15) compared to IPM (72.13 ± 5.51) plots. Individual fruit weights were not statistically different (P = 0.071), but IPM melons (6.76 ± 0.18 kg) tended to be larger than those from CM (6.22 ± 0.23 kg) fields. Yield data only included fruit deemed marketable without any rind damage from insect feeding or other deformities. IPM watermelons experienced an increased number of damaged fruits (55 deemed unmarketable in IPM with only 1 in CM fields); this represented a <5% loss in potential yield.
There was no relationship between total pollinator visitation and crop yield, likely due to the high stocking of managed honey bee colonies in both pest management systems. To test this possibility, we separately analyzed honey bees apart from the wild bee community. This subset analysis confirmed that honey bee visitation could not predict watermelon yield (Fig. 4A; overall slope, P = 0.097), whereas higher rates of wild pollinator visitation, driven by lower insecticide use, resulted in correspondingly higher watermelon yield (Fig. 4B; overall slope, P = 0.043; CM slope, P = 0.218; IPM slope, P = 0.728).
Honey bees (A) did not predict watermelon yield, but increased wild pollinator visitation (B) in the IPM fields resulted in higher watermelon yield. All plots were stocked with two honey bee colonies at opposite corners of the field. Each point is the total number of observed pollinator visits at a field per site (n = 5 sites with 225 observation minutes) and the corresponding site’s average watermelon yield. Best-fit trend line shows relationship using regression model with P < 0.05. Bee icons from BioRender.
IPM Was More Profitable than Conventional Management.
The product cost (i.e., no application cost) of Cruiser 5FS on corn was $31.10 ⋅ ha−1; however, using industry-provided data (53), the inflation-adjusted cost of an NST at the rate applied in this study was $57.79 ⋅ ha−1. Using this cost calculation and the range of field sizes, the use of an NST in CM corn represented a cost of $330.93 ± 30.93 ⋅ field−1. The cost relative yield (CRY; the minimum percentage in yield gain in which the insecticide cost is recuperated) was 3.3%, which was not reached in either the CM/IPM experiment or the within-site NST evaluation, indicating that the cost of NST was not recovered at any of the sites in this experiment.
Watermelon insecticides in the CM system cost $44.05 ⋅ ha−1 for the soil drench and $50.28 ⋅ ha−1 for all foliar insecticide applications ($12.57 per application) for a total cost of $94.33 ⋅ ha−1 on each field with additional applications required to control secondary pests in some fields, increasing this cost. While several insecticide sprays were applied to the IPM watermelons, this was a minority of fields, leading to an average cost for IPM insecticides at $3.35 ± 1.44 ⋅ ha−1 compared to $100.98 ± 3.49 ⋅ ha−1 across the CM watermelon fields. The insecticide program for CM watermelons had a CRY of 0.70%; however, all fields within the CM system failed to reach this threshold, and the insecticide applications were never cost-effective. The increased yield from wild pollinator enhancement in the IPM system would result in a financial gain of $4,512.69 ⋅ ha−1 over the CM system, based on the previous 5-y regional sale price for seedless watermelon (52).
Discussion
IPM-based approaches, ones that prioritize treating only when insect pests are present at damaging levels, have become increasingly rare across a range of commodities. Instead, a suite of prophylactic approaches to pest management—including insecticidal seed treatments, soil drenches, and calendar sprays—now dominate most US cropping systems, including the corn and watermelon systems studied here. However, our comprehensive field experiment demonstrates that there is no clear rationale supporting this approach from multiple perspectives including insect pest damage and abundance, pollinator visitation and efficiency, environmental pesticide residues, or crop yield and profitability. These varied and integrative perspectives are vital for grower adoption but surprisingly rare in practice. Hundreds of studies, for example, have tested the negative effects of neonicotinoids and related insecticides on pollinator health in the laboratory and field. The potential threat from these products is incontrovertible. Yet pollination alone paints an incomplete picture without corresponding data on pest population dynamics and crop production. In previous studies that experimentally reduce insecticide use in crops to determine impact on pollinators, the implications for pests and crops are typically overlooked or omitted [e.g., canola (54), cucurbits (49, 55), apples (56), and sunflowers (57)]. Similarly, in studies in which landscape complexity is used as a predictor of pollination services (58, 59), wholesale changes in pest management practices are not explicitly measured or discussed. Farmers are unlikely to change their management practices—no matter how detrimental to bees—if foregoing insecticide treatments leads to excessive crop and economic damage. Conversely, studies on pest/yield relationships [with limited exceptions (60, 61)] involve self- or wind-pollinated crops (7, 11, 62). These experiments often fail to capture the additional losses to yield that nearby or adjacent crops could experience—even though, in some cases, the landowner/crop producer is the same individual.
Insecticide Use, Pest Outbreaks, and Crop Yield.
One expected corollary of reducing insecticide inputs over years of the experiment was an increase in pest densities over time. Surprisingly, the only evidence of increasing pest pressure on untreated corn was higher damage from rootworm larval feeding in year 4. To isolate the effect of NSTs with minimal confounding factors, corn in our experiment was grown somewhat atypically: without any Bt traits or crop rotation. Therefore, IPM corn was cultivated under a “worst-case scenario” with no protection for the duration of the study. Despite being entirely defenseless for four consecutive years, only three of the five fields experienced increased root feeding and only in the final year. These locations were at the northernmost sites, which is the region of the state, where rootworm pressure is historically highest (63). This outcome demonstrates that corn rootworm populations in major production areas should not be left unchecked and can increase in a relatively short time but that the industry standard of Bt corn with soybean rotation likely maintains rootworm at sufficiently low levels. It is also important to note that, while we focus on rootworm as the primary corn pest, and one for which we observed some evidence of feeding damage, NSTs are largely marketed as targeting secondary pests (e.g., wireworm and seedcorn maggot). These taxa were not present at appreciable densities in any of our experimental fields. Although these cryptic belowground insects are hard to directly sample, indirect evidence of their presence and impact (e.g., poor plant stand in early-season corn) was never observed.
Despite the rise in rootworm damage over time in NST-free corn, yields were not significantly different across the two systems, reinforcing other published studies that show no yield benefit from NSTs (8, 11, 14). Interestingly, the only factor impacting corn yield had nothing to do with insecticide use. We observed gradual but consistent reductions over time with year 4 yields 28% lower than year 1 yields. This effect was apparent across both IPM/CM treatments. The outcome is not surprising, as numerous studies have documented that single-species cultivation has negative feedbacks on crop productivity, including corn (64). These data strongly point to crop rotation as a factor in maintaining high corn yields and likely far more critical in mitigating rootworm damage than NST use (12). For the purposes of this study, we more narrowly defined IPM in the context of insecticide use, but a “true” IPM system would employ crop rotation rather than continuous cropping.
Unlike corn, the key insect pest in IPM watermelon colonized in the initial year and was present at moderate densities throughout the entire experimental period, but, similar to the corn system, these elevated densities did not translate to yield reductions, even using the fairly liberal threshold of five beetles per plant. These data suggest that watermelon should be routinely scouted to protect against the rare site or year in which pests, like cucumber beetles, exceed their threshold but can mostly be cultivated without insecticide use (65⇓⇓–68). Notably, we only observed outbreaks of secondary pests—aphids and mites—in the CM system, in which we repeatedly treated the crop with insecticides. Cucurbit growers in our region frequently mention these as pests of concern; however, many of these same producers also use repeated applications of pyrethroids and neonicotinoids (69), compounds that are highly disruptive to beneficial insect communities that suppress aphid and mite populations (70). Altogether, these observations imply that overly aggressive treatment with broad-spectrum insecticides trigger secondary pest outbreaks in watermelon and that adopting a scouting-based IPM program with fewer inputs prevents the problem.
A major challenge to scouting adoption is that the CRY for watermelon is <1%, reflecting the reality that insecticides such as pyrethroids are inexpensive relative to other farm inputs (e.g., labor). Moreover, our CRY calculations do not account for the additional cost of scouting in IPM systems, which can be challenging to estimate (69). Some growers scout their own fields for pests, while others hire crop consultants. Similarly, scouting a subset of fields or sporadically observing a few edge plants (versus walking transects with a specified sample number and location) will undoubtedly reduce costs but also accuracy. In our experiment, insecticide costs were ca. $101 ⋅ ha−1 in CM compared with $3 ⋅ ha−1 in IPM. Thus, scouting would need to add at least $98 ⋅ ha−1 to offset the difference. Other factors that affect the reliability of this estimate include the additional cost (e.g., fuel, equipment, and labor) of repeated insecticide applications in CM fields and variation in insecticide price or efficacy. Despite these complexities, Ternest et al. (69) found that the cost of seasonal pest scouting ranges from $29 to $120 for a field, well within our estimated price point for a commercial watermelon grower to see a positive return from scouting.
The economics of scouting and IPM as a whole also vary widely across cropping systems. We primarily consider watermelon for which crop value is relatively high, fields are relatively small, and the pests are mostly aboveground and can be controlled with insecticide sprays. In large acreage row crops such as corn with belowground pests that are both hard to sample and lacking immediate rescue-treatment options, the cost/benefit ratio of scouting may be less favorable. Even among specialty crops, we expect the net value of IPM to be highly variable. Watermelon exhibits a few features that could tip the balance in favor of IPM. Compared with other cucurbits, for example, watermelon has a much higher pest threshold due to its natural resistance to the SCB-transmitted bacterial wilt (Erwinia tracheiphila) that kills infected plants (71). Also, seedless watermelon has among the highest reliance on bee pollination (72) and, consequently, the risk of insecticide overuse disrupting fruit production is correspondingly greater in this system. Specialty crops with lower pest tolerances and pollination requirements or those produced in regions with higher pest pressures will experience vastly different trade-offs. These relationships are also dynamic and need to be reevaluated regularly over time. In our region and many other parts of the world, insect invasions [e.g., brown marmorated stink bug (73), spotted winged drosophila (74), and spotted lanternfly (75)] result in a constantly changing landscape of pests and the economics underlying their management.
Routes of Insecticide Exposure for Pollinators.
Neonicotinoids were consistently found at higher levels in the pollen of both crops within the CM system compared to IPM. The specific concentrations detected are comparable with related studies. For instance, squash pollen contained 15 to 19 ng/g of imidacloprid 7 wk postapplication (76) compared to a median value of 6.28 ng/g in this experiment. A trial across the cantaloupe flowering period ranged from 3 to 141 ng/g imidacloprid (77), demonstrating the wide range of potential exposure. Some of this variation is likely explained by bloom time, as we documented much higher levels in early than late flowers. This temporal effect is not trivial. Growers receive price premiums for early melons, and these data indicate that the most valued early flush of flowers are the ones that are most heavily contaminated with neonicotinoids.
Bees were also likely exposed via soil residues. Recent studies emphasize the significance of soil-derived neonicotinoid exposure for ground-nesting bees, including imidacloprid in cucurbits (48, 49, 55). This difference in exposure could partly explain why we observed treatment effects on floral visitation for wild bees (most of which are ground nesters) and not managed honey bees. However, this differential response among pollinators is likely driven in part by other factors inherent to honey bee biology and management (e.g., hives are stocked at high densities, with >20,000 individuals per colony; large individual body size, and thus pesticide tolerance, compared to many solitary wild species). A recent field experiment on commercial cucurbit farms in the midwestern United States similarly found that insecticide use reduces wild bee visitation with no corresponding effect on honey bees (78). This effect is notable, since wild bees in our experiment were both most sensitive to insecticide use and most strongly correlated with crop yield. The latter outcome should be expected—wild bees, in general, are more efficient than honey bees as crop pollinators (79⇓–81), and in watermelon, wild bees are more than twice as effective on a per-capita basis in promoting fruit set and growth (81, 82).
A limitation of our experimental design is that we are unable to differentiate the relative influence of corn and watermelon inputs on crop pollination, since the two are confounded (i.e., we did not independently manipulate insecticide use across the two crops in a factorial design). Because the crops were treated with different neonicotinoids—thiamethoxam in corn and imidacloprid in watermelon—we can infer mobility and exposure across these crop types by interpreting residues from these active ingredients. Clothianidin, for example, was detected at low levels in 72% of CM watermelon pollen in 2019 compared to 0% in IPM pollen despite never being applied to watermelon in either treatment. These patterns suggest that watermelon roots scavenge these compounds from a pool of soil residues derived from either ground water movement from the surrounding corn or carryover effects due to the prior year’s NST corn planting. Another likely possibility is that highly mobile bees foraged across crop boundaries, which were well within the flight radius of most taxa. Generalist pollinators like bumble bees tend to avoid cucurbit pollen (83) and readily forage on corn pollen when little else is available (84). Indeed, we observed few bumble bees foraging on watermelon flowers (<10% of visits; SI Appendix, Fig. S5) despite stocking fields with managed hives. However, more information is needed on the foraging ranges and behaviors of nonhoney bee taxa across crop boundaries; for example, the longhorn bee Melissodes bimaculatus is an extremely common, mobile, and effective wild pollinator, but its movement within or between crop fields is poorly documented.
A final outcome worth emphasizing is the speed with which the pollinator community responded to IPM implementation. Improvements to bee visitation and yield were observable rapidly, in the first year of the experiment (Fig. 2), even though these farm sites were conventionally managed in previous years and surrounded by conventional agriculture. The response did not require multiple years of insecticide reduction or installation of pollinator habitat. There is a perception that farmland in its current state is devoid of natural life, but these data show that reduced inputs alone, independent of habitat or land use changes, can have demonstrably positive effects in the near-term.
Conclusion
One of the central challenges of global food security in the 21st century is ensuring adequate food supply for a growing population while conserving natural resources. These are often viewed as contradictory endeavors (i.e., a trade-off between agricultural productivity and conservation). Indeed, “feeding the world” is a common rationale for excessive pesticide use and insurance-based pest management approaches in crop protection. Yet, increasingly, studies find that substantially lower pesticide inputs result in equivalent yields (85), suggesting that high productivity can be maintained—or even increased, as shown in our study—with less intensive management. This finding dovetails the recent call for ecological intensification of agriculture, for which IPM adoption is a central theme (86⇓–88).
Overall, our study demonstrates that the current, prophylactic approaches offer no consistent benefits to offset the demonstrably negative impacts to both pollinators/pollination and crop yields. The convenience of NST and calendar sprays to manage pests is clearly attractive to some producers. However, this argument rests on the twin assumptions that 1) populations of target pests can be expected to be at economically damaging populations each year, and 2) monitoring-based IPM alternatives expose producers to higher risks and/or upfront costs. Our data do not offer support for these claims in either cropping system and, in fact, show that embracing the use of IPM may offer a readily available “win-win” scenario for crop production and pollinator health across diverse crops.
It is important to note that conducting pest surveys with economic thresholds is not a new phenomenon; thus, our approach was not revolutionary and did not reinvent the wheel. The tools, in principle, have been established for decades, even if they have fallen out of practice. A key step forward is better understanding the thought process underlying when and why farmers decide to use insecticides. There is a myth that farmers only care about profit and refuse to monitor pests because it is too much effort or too time-consuming. Neither of these seem to be universally true. In a recent grower survey of reasons for implementing action thresholds, saving money on insecticide sprays was not among the top three responses and ranked beneath “less harmful to the environment” (89). Similarly, “reducing scouting” and “convenience” were among the bottom several reasons when soybean farmers were surveyed about their pest management decisions in the context of seed treatments, whereas “protecting water quality” and “public safety” were among the top factors (90). These trends are validated by the success of previous extension-based programs in helping growers adopt IPM tactics (89). However, IPM adoption has a long and rocky history that extends far beyond grower education efforts (91⇓⇓⇓–95). This circumstance is particularly complicated for seed treatments in which growers may not be making explicit decisions to use neonicotinoids, since they are typically the default option offered by seed suppliers (16). In this case, an “extended peer community” that engages farmers, consumers, industry, government, and conservation programs will be vital (96) while ensuring that choice is maintained in crop seed sales and that growers are provided with clear guidelines for how to implement scouting using scientifically backed pest thresholds.
Materials and Methods
Site and Experimental Design.
The experiment was conducted over 4 y (2017 to 2020) on five research farms at the Purdue Agricultural Centers (PACs) located across Indiana (SI Appendix, Fig. S1): Northeast (NEPAC; Columbia City, IN), Pinney (PPAC; Wanatah, IN), Throckmorton (TPAC; Lafayette, IN), Southeast (SEPAC; Butlerville, IN), and Southwest (SWPAC; Vincennes, IN). These sites are positioned along a latitudinal gradient across the state with at least 100 km separating one another, ensuring that sites represent a diversity of climatic conditions, soil types, and local pest pressures.
Each site contained of a pair of agricultural fields that were randomly assigned to either a CM or IPM program. These treatments were designated in year 1 of the study (2017) and remained within this management system for the duration of the experiment. CM systems were considered the “industry standard” and were designed to mimic the pest management regime typically found in both row crops and vegetable production, including the routine use of prophylactic insecticides. The IPM system was an experimental treatment that relied on pest scouting to determine the use of insecticides. We only applied insecticides as needed based on published action thresholds as specified in SI Appendix, Supplemental Methods. Within a site, paired fields were separated by an average of 5.6 km (range: 4.63 to 6.63 km), which resulted in similar abiotic conditions (e.g., temperature and precipitation) while providing sufficient buffer for biological independence of CM/IPM treatments, as insect pollinators are unlikely to fly >5 km (97).
Cropping Systems.
Fields (area mean: 5.74 ha, range: 4.82 to 7.73 ha) were planted continuously with corn in all 4 y of the study. While corn–soybean rotation is common in the midwestern United States (72.3% of all corn acreage in key corn producing states—Iowa, Illinois, and Indiana—from 2015 to 2019), continuous corn is the next most prevalent system, constituting 24.7% of acres (52). Starting in year 2 of the study (2018) and continuing for three growing seasons, we planted a 0.2-ha watermelon plot embedded centrally within the corn matrix (SI Appendix, Fig. S2). Corn is the dominant crop grown in Indiana and throughout much of the Midwest (11.74 million ha across Iowa, Illinois, and Indiana). Thus, this design is a microcosm of midwestern US agriculture, in which pollinator-dependent crops such as watermelon are bordered, and often completely surrounded, by corn. The goal of this design was to document the effects of large field crop plantings upon other, adjacent cropping systems. Corn was planted 1 y in advance of watermelon because neonicotinoid exposure can occur both in season through a variety of exposure routes or from the previous year’s inputs. This aspect of the experimental design reflects that the vast majority of watermelon acreage on Indiana farmland (77%) is in rotation with either corn or soybean (52). Management practices (e.g., tillage, irrigation, fertilizer, herbicides, and fungicides) were standardized across sites such that the only factors differentiating CM/IPM field pairs were insecticide inputs (refer to SI Appendix, Supplemental Methodsfor management details and field histories).
All corn seed (Spectrum 6334) across both treatments received a fungicide seed treatment (Maxim Quattro: azoxystrobin 2.5 µg; fludioxonil 6.5 µg; mefenoxam 5 µg; thiabendazole 50 µg active ingredient [a.i.] ⋅ seed−1); however, CM corn seed was also treated with the neonicotinoid thiamethoxam applied at the maximum rate, marketed for control of corn rootworms and a suite of other secondary pests (Cruiser 5FS at 1.25 mg a.i. ⋅ seed−1). By 2012, >80% of all US corn seed was coated with at least one neonicotinoid (15), and the CM treatment thus represents the corn seed most commonly used by US farmers. Throughout the experiment and in both treatments, we used a nontransgenic variety that did not express Bt toxins (Bacillus thuringiensis), meaning that the untreated IPM seed was unprotected from larvae of the western corn rootworm (D. virgifera virgifera LeConte), the key corn insect pest in the region, and other soil insect pests. This allowed for a “true” assessment of the efficacy of NST impacts on pest control without the confounding effects of multiple, layered plant protection technologies. However, in practice, all corn seed sold in the United States that expresses Bt toxins is also treated with at least one neonicotinoid insecticide (98).
We used a seedless watermelon system, which requires triploid and diploid plants interspersed with one another. All watermelon fields contained the triploid variety ‘Fascination’ as the seedless crop along with the diploid var. SP-7 as the pollenizer at a 3:1 ratio to ensure adequate pollination. At transplant, CM watermelons were treated with the neonicotinoid imidacloprid (Wrangler at 814.09 mL/ha) as a soil drench at the high rate, while IPM watermelons received no insecticides. Additionally, CM watermelons were sprayed with the high rate of the insecticide lambda-cyhalothrin (Warrior II pyrethroid at 140.3 mL/ha) via tractor-drawn air blaster or boom sprayer at 4, 6, 8, and 10 wk posttransplant, resulting in four foliar applications each season. Application rates for both insecticides (standardized by milliliter a.i. per hectare; lambda-cyhalothrin = 31.98, imidacloprid = 316.43) are within the range recommended by the label (lambda-cyhalothrin = 21.32 to 31.98, imidacloprid = 237.94 to 356.91). Similarly, insecticide rates used in the experiment are slightly higher than, but comparable to, those applied by watermelon growers in our region, according to on-farm pesticide records reported in ref. 69: lambda-cyhalothrin (n = 18 applications; mean = 26.93, median = 26.66, range = 16.66 to 33.32), imidacloprid (n = 7 applications; mean = 293.92, median = 297.43, range = 250.22 to 328.41).
Although watermelon insecticide regimes across growers are more diverse than corn, our prior on-farm survey of insecticide use on 17 Indiana watermelon farms found that producers averaged ∼5 treatments per field per season, and thus the five applications in the CM treatment (1 soil drench + 4 foliar sprays) were intended to reflect this practice (69). The survey further revealed that pyrethroids, including lambda-cyhalothrin, were the three most used active ingredients. Neonicotinoids, including imidacloprid, were also used but at lower frequencies (30% of watermelon growers in ref. 69). These data guided our pyrethroid-biased regime in the CM treatment. Watermelons in the IPM treatment were left untreated unless insect pests exceeded economic thresholds at a site (see Insect Pest Abundance and Damage), in which case the field was also treated with a foliar spray of lambda-cyhalothrin, as described for CM fields. Additional details on corn and watermelon management (e.g., planting dates and seeding rates) are provided in SI Appendix, Supplemental Methods.
The watermelon–corn matrix was supplemented with managed bees to replicate the pollination practices used by commercial watermelon growers, who typically either rent honey bee hives from beekeepers or purchase bumble bee hives. Increasingly, growers in our region stock with both honey bees and bumble bees in the same field due to their foraging at different times and weather conditions. In each field, two honey bee colonies were placed on opposite corners at the edge of watermelon plots in an arrangement that avoided interference with pesticide application. This stocking rate (1 hive per 0.1 ha) falls within the recommended range for commercial production used by regional growers (99). Additionally, one Quad pollination hive (Koppert Biological Systems) containing four bumble bee (Bombus impatiens) colonies was placed in each field at 4 to 5 wk posttransplant to synchronize activity with the watermelon bloom period.
Insect Pest Abundance and Damage.
Corn plants were evaluated for both early- and late-season pest damage to assess the efficacy of insecticidal seed treatments. Because foliar insect pests were rarely observed, sampling focused on the more economically damaging guild of soil-dwelling root pests. First, corn stand was evaluated at the V3 to V4 stage, along six 5.3-m transects down a row, in which the number of emerged plants was counted. Transect counts were averaged and extrapolated to estimate plants per hectare and compare with known planting densities. Poor corn stand, relative to initial planting rates, is often an indication of belowground seedling damage by insects including wireworms and seedcorn maggots (100, 101). At corn anthesis, root damage was quantified to determine potential for lodging due to corn rootworm feeding. In every field, 10 random plants were excavated along each of four transects that were >20 rows from the field edge with >10 m separating sampled plants within a transect. The root mass was then rinsed and evaluated for damage using the Oleson injury rating scale (102), the established approach for assessing rootworm feeding.
Beginning the week following transplant, watermelon plants were surveyed for pests weekly for a 10-wk period extending to harvest. Each survey consisted of five randomly positioned transects, with plants sampled at 10, 20, and 30 m from the plot edge (n = 15 plants per plot per week). For each plant, all aboveground tissue was inspected, and the identity and number of insect pests found on the plant or the soil directly below were recorded. If the density of the primary pest, SCB A. vittatum (F.), exceeded the economic threshold of five adult beetles/plant, then the plot was treated with a foliar spray of lambda-cyhalothrin within 2 d of the observation (103). Refer to SI Appendix, Supplemental Methodsfor additional details on pest scouting protocol.
Watermelon Pollinators.
To assess pest management impacts on pollination, we conducted visual observations of watermelon flowers to quantify pollinator visits and community composition. Flower clusters, consisting of at least five male and one female flower, were observed for a 3-min period, during which pollinator type, number of flowers visited, and transition of pollen from a male to female flower (i.e., a pollination event) were recorded. Behavioral observations were conducted on the same date at both fields at each site. First observation began 5 to 6 wk posttransplanting and continued for 5 consecutive weeks to encompass most of the blooming period that contributes to harvested yield. Refer to SI Appendix, Supplemental Methodsfor more detail on sampling design.
Crop Yield.
Corn maturity was monitored, and the crop was harvested during each of the 4 y to assess the impact of NSTs on yield. All yield reports were adjusted to account for variation in moisture at harvest, and data were standardized to a 15.5% moisture content.
Because corn yields were strongly affected by local factors (e.g., soil type, pH, and drainage) determined by random field assignment, we conducted a separate companion study in 2019 using the same two corn seed treatments. This higher-resolution study focused exclusively on yield in smaller, more highly replicated plots with both treatments (neonicotinoid-treated versus untreated) included in the same field to control for site variation. The trial was repeated at six sites; four of the five original PACs used in the experiment (all but SEPAC) and two additional locations (Davis PAC in Farmland, IN, and the Agronomy Center in West Lafayette, IN). At each site, we planted four to nine replicates of two adjacent 5.3-m-length rows of each corn treatment in a randomized complete block design with the same planting date across all replicates at each site (n = 33 total plot replicates for both treated and untreated seed). At harvest, the weight and moisture adjusted yield for each replicate was extrapolated to a per-hectare yield.
Beginning at fruit maturity (approximately 80 d), five randomly positioned subplots (5 × 2 m area) of each watermelon field were hand-harvested and used to estimate yield. Mature fruits from each subplot were counted, weighed, and inspected for marketability using US Department of Agriculture (USDA) grading standards (104) for lack of physical deformities or disease. Subplots were harvested weekly for four consecutive weeks, after which data were summed over time to calculate a total yield per unit area.
Pest Management Profitability.
Cost of insecticides applied were either calculated from direct expenditures from purchased product or sourced from external guides (105). The cost of the product (Cruiser 5FS) applied as an NST could be quantified but fails to account for additional costs of seed treatment practices that include labor, infrastructure, specialized equipment, and transportation. A proxy for this calculation can be used based on industry-provided costs for the other commonly used neonicotinoid in corn pest management, clothianidin (53). We also calculated the CRY, which is interpreted as the minimum percentage in yield gain required to cover the cost associated with an insecticide treatment and reach a breakeven point at which the treatment cost is recuperated (6, 106, 107). CRY was calculated by dividing the insecticide treatment cost by the crop price × crop yield. For both watermelon and corn, price and yield were based on the previous 5-y average (2016 to 2020) from the state of Indiana (52).
Pesticide Residues.
Samples of soil, watermelon leaf tissue, and corn and watermelon pollen were collected during each of the 4 y and analyzed to detect residues of insecticides and fungicides applied to both corn and watermelon crops using the QuEChERS procedure, followed by liquid chromatography–tandem mass spectrometry (LC-MS/MS) for pesticide identification and quantification. Refer to SI Appendix, Supplemental Methodsfor sample number, preparation, and analytical details.
Statistical Analysis.
All statistical analyses were performed using SYSTAT 13 (SYSTAT Software, Inc) by creating a series of general (continuous data) or generalized (discrete data) linear models. To avoid pseudoreplication, all data points were condensed to a single year/site/treatment to be used in the model by taking the mean for damage evaluations across dates and yield measurements within a field as well as summing pest counts or pollinator measurements across observation dates for each field. This process resulted in 40 and 30 data points for corn and watermelon, respectively, per response variable; crop differences were due to corn being cultivated for one extra year (2017) than watermelon (Cropping Systems). Stand counts were natural log–transformed, while root damage at each site was summed and multiplied by 100 to produce integer values and then fit to a zero-inflated distribution. SCB counts and pollinator surveys were summed as total number of beetles or pollinators at each field, to maintain discrete integer values, and fit with a negative binomial distribution. Corn and watermelon yield data were normally distributed and remained untransformed. Models used year (n = 4 corn, n = 3 watermelon), site (n = 5), and management treatment (n = 2) as fixed effects as well as two-way interactions between treatment and year or site. Post hoc pairwise comparisons (Fisher’s least significant difference) were used to differentiate any factors (or interactions) that were significant. Within-field corn yield assessment was analyzed in a separate mixed model with the use of NST and site (n = 6) as fixed effects and spatial block as a random effect. The relationship between crop yield and pollinator visits was explored with regression analysis with a fixed effect of treatment. This relationship was tested against the number of visits from honey bees and the wild pollinator community to contrast the effect from managed versus wild pollinators. Raw data generated from this study are publicly accessible in the Purdue University Research Repository (109).
Data Availability
Raw data have been deposited in the Purdue University Research Repository (DOI: 10.4231/4DQF-3G13).
Acknowledgments
We thank the staff at all Purdue Agricultural Centers for assistance in planting, harvesting, and maintenance of fields throughout the experiment, especially Dennis Nowaskie for providing expertise on watermelon production. Dr. Dan Egel, Dr. Amanda Skidmore, Larry Bledsoe, Krispn Given, and John Ternest aided in sampling methodology and provided assistance. Thanks to Amber Jannasch and Yu Han-Hallett for assistance with pesticide extraction methods and analysis protocols for all residue samples. Additional thanks to all the students and staff for help with both field and lab work: Gabriella Altmire, Jennifer Apland, Jessica Gasper, Wadih Ghanem, Iván Grijalva, Robert Grosdidier, M. Ross Hunter, Nick Johnson, Molly Jones, Chasidy Kissinger, Maisha Lucas, Taylor Nelson, Catherine Terrell, Julie Smiddy, Rachael Topolski, Tyler Vandermark, and Dillon Woolf. This research was supported with funding awarded to I.K. from the USDA/National Institute of Food and Agriculture Grant 2016-51181-25410.
Author contributions: J.R.P., L.L.I., R.E.F., C.H.K., and I.K. designed research; J.R.P. and L.L.I. performed research; J.R.P. and I.K. analyzed data; and J.R.P., L.L.I., R.E.F., C.H.K., and I.K. wrote the paper.
Standardized monitoring has revealed that the total number of moths has declined steadily by one third over the last 50 years (1968–2017). Pictured are two of the 2,500 moth species found in the UK (Left is a Elephant Hawk-moth, and right is a small Elephant Hawk-moth). Credit: Douglas Boyes
As insect populations—including bees, moths, and other pollinators—decline worldwide, researchers have established a variety of potential causes, including climate change, pesticides, and habitat loss. But now, new findings suggest yet another culprit may be part of the equation: night-time lighting, like street lights in populated areas.
A team of entomologists in the United Kingdom looked at populations of moth caterpillars under street lights, compared to populations that lived in darkness all night. In conditions with night-time lighting, they found nearly half as many caterpillars, in some cases. In addition, caterpillars that grew up under street lights were bigger, suggesting that they might be stressed and attempting to rush into metamorphosis earlier than they should. Furthermore, the greatest threat seems to be coming from energy-efficient LED lights, whose bluer wavelengths may be more stressful than the warmer, redder light of older sodium bulbs.
LED streetlights at a rural junction in Curbridge, Oxfordshire. Credit: Douglas BoyesSampling nocturnal caterpillars in grass margins using a sweep net under white LED street lights in Golden Balls Roundabout, Oxfordshire. Credit: Jacob Jaffe
A selection of moth caterpillars caught by sweep netting under streetlights (mix of several species, family: Noctuidae) during fieldwork at night. Credit: Douglas Boyes
Fires may have affected up to 85 percent of threatened Amazon species
ScienceNews
Since 2001, an area up to the size of Washington state has burned
A fire burns trees in the Amazon basin in Brazil’s Maranhão state in 2014. Fires like these are searing the geographic ranges of thousands of Amazonian species, an analysis of nearly 15,000 plant and vertebrate species finds.MARIO TAMA/GETTY IMAGES
The extent of the damage is closely tied to the enforcement, or lack thereof, of regulations in Brazil aimed at protecting the forest from widespread logging as well as the fires often used to clear open space in the forest and other encroachments. The findings illustrate the key role that forest use regulations have in the fate of the Amazon rainforest, the researchers argue.
Threats to the survival of this biodiversity could have long-term effects. Biodiversity boosts a forest’s resilience to drought, says Arie Staal, an ecologist at Utrecht University in the Netherlands who was not involved with this research. A deep bench of tree species allows the plants to replace those that may not survive drought conditions, he says. “If fire-impacted area continues to rise, not only does the Amazon lose forest cover, but also some of its capacity to cope with the changing climate.”
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And as fires advance deeper into the rainforest, more species will experience fire for the first time, Staal says. “These species, including many threatened ones, have not evolved under circumstances with regular fires, so the consequences for those species can be severe.” Such consequences may include increased risk of population declines or extinction, similar to the fears following the major outbreak of fires in Australia in 2019 and 2020 (SN: 3/9/21).
In recent decades, ongoing deforestation and periodic drought in the Amazon basin have been associated with intensifying fires there (SN: 11/20/15). In 2019, a particularly severe series of fires scorched the region (SN: 8/23/19).
“But we do not know how fires are impacting the biodiversity across the Amazon basin,” says Xiao Feng, a biogeographer at Florida State University in Tallahassee. The Amazon “is a huge area, and it is generally impossible for people to go there and count the number of species before the fire and after the fire,” he says. “That’s an incredible amount of work.”
So Feng and a team of collaborators from Brazil, China, the Netherlands and the United States instead investigated how Amazonian plant and animal species’ geographic ranges have been exposed to recent fires. The team compiled range maps of 11,514 plant and 3,079 vertebrate species, creating what may be the most comprehensive dataset of range maps for the Amazon. The team compared these maps with satellite images of Amazon forest cover from 2001 to 2019. Those images let the team track how logging and fires have led to the degradation of rainforest habitat.
Fire impacted up to about 190,000 square kilometers — an area roughly the size of Washington state, the team found. Up to about 95 percent of the species featured in the study had ranges that overlapped with fires during this period, though for many species, burned areas made up less than 15 percent of their overall range.
Affected species include up to 85 percent of the 610 considered threatened — so vulnerable to extinction or already endangered or critically endangered — by the International Union for Conservation of Nature. This category includes as many as 264 kinds of plants, 107 amphibians and 55 mammals. In 2019 alone, over 12,000 species experienced fire somewhere in their geographic range.
From 2001 to 2019, the endangered white-cheeked spider monkey (Ateles marginatus) has had up to about 6 percent of its Amazon forest range affected by fire, researchers say.IGNACIO PALACIOS/GETTY IMAGES PLUS
Starting in 2009, when a series of regulations aimed at reducing deforestation started being enforced, the extent of fires generally decreased, except in drought years, the team found. Then in 2019, fires ticked back up again, coinciding with a relaxation of regulations. Much of the fire-driven forest loss was congregated along the more intensely logged southern reaches of the rainforest.
The shift suggests that effective forest preservation policies can slow this trend of destruction, and may be crucial for preventing the region from reaching a tipping point. That point would occur when the cycle of deforestation, drying and fire triggers widespread transformation of the Amazon basin into a savanna-like habitat.
While this study couldn’t track the fate of specific plants or animals, Feng now plans to look at fire’s impact on certain groups of species that may have very different vulnerabilities to an increasingly flammable Amazon. “We know some trees may be more resistant to burns, but some may not. So it may also be really important to distinguish differences,” he says.
Jake Buehler is a freelance science writer, covering natural history, wildlife conservation and Earth’s splendid biodiversity, from salamanders to sequoias. He has a master’s degree in zoology from the University of Hawaii at Manoa.
People in New Zealand have cut down so many trees, some native insects are losing their wings.
In the space of 750 years, humans have changed the natural landscape of the country’s South Island so much, scientists say it’s causing rapid evolutionary changes among certain species.
With no more alpine forest to break the strong mountaintop winds, at least one type of insect is already transitioning out of the flight industry.
Zelandoperla fenestrata is a stonefly with two distinct phenotypes: one with wings, capable of flight; and one with stunted wings or even none, described as flightless.
The flightless type of stonefly is usually found at higher altitudes, where trees are scarce and strong winds can therefore easily blow a flying insect out into the abyss. Meanwhile, the flight-capable flies are typically sheltered in alpine forests, where insects need to explore the full extent of the habitat.
However, in regions where alpine forests have been cut down, researchers have noticed something intriguing. The insects at this elevation, which should usually be able to fly, can’t do so.
It appears that human-caused deforestation has indirectly deprived these insects of their ability to fly, and we did so in a very short space of time, evolutionarily speaking.
Widespread burning of native forest commenced shortly after Māori arrival sometime after 1200 CE, and by now, more than 40 percent of the forests that once covered New Zealand’s South Island have been transformed into grassland and fern-shrubland. Even though this was the last major landmass to be developed by humans, we are already seeing the evolutionary impact on local wildlife.
The now-flightless stonefly is likely just the tip of the iceberg.
“In addition to the local shifts inferred here, it is likely that widespread deforestation has increased the proportion of flightless lineages across large areas of southern New Zealand,” the authors write.
The team worries that without wings, stoneflies won’t be able to search for mates in a larger territorial range, thus increasing genetic diversity. This could possibly impact the species’ health in the long run, as well as the insects’ risk of extinction.
In a rapidly changing world where so many other insects are dying out, that fear isn’t unfounded. By removing the forests that once sheltered stoneflies, we are changing the very way the wind blows.
The authors admit there are probably factors other than wind that make insect flight unappealing on an open mountaintop – such as habitat stability and temperature – but they argue these powerful gusts are the most prominent feature of New Zealand’s mountaintops.
Charles Darwin would probably agree with that conclusion. More than a century and a half ago, Darwin and the botanist Joseph Hooker got into a fiery debate over why so many insects can lose their wings, when they are clearly such useful appendages.
On the islands between Antarctica and Australia, the two scientists had noticed almost all the insects had lost their wings. Even the flies didn’t fly anymore.
Despite skepticism from his colleague, Darwin contended that the wind was to blame. If an insect tries to fly on an open landscape like this, it will simply get swept out to sea. In this situation, the flightless phenotype will always win.
In recent years, his simple hypothesis has gained more support. In 2020, for example, researchers indeed found wind plays a major role – albeit not an exclusive one – in the loss of insect flight on remote islands of the Southern Ocean.
In the case of the New Zealand stonefly, researchers suspect the presence of water, the amount of light or the productivity of the population, can all dictate whether an insect population will fly or not.
In all likelihood though, wind, as Darwin once predicted, blows all those factors away.
It’s not just bees and butterflies that are under threat: UConn entomologist and Professor David Wagner says all kinds of insects are at risk for “a death by a thousand cuts.” This is alarming, since insects play vital roles in earth’s ecosystems, including pollination of plants, driving food webs around the planet, and cycling nutrients.
The insect decline is attributed to multiple factors, including the climate crisis, agricultural intensification, development, deforestation, and the introduction of exotic and invasive species into new environments. Wagner cautions that many of these creatures will not be with us for much longer, and says people must act swiftly to help prevent these tremendous losses before it is too late.
Wagner remains hopeful, and says there are many actions that can be taken now—from encouraging political leaders to enact policy changes, to simply letting part of the front lawn grow freely to provide a food-rich environment for insects.
Field margins are important habitats and networks for nature and they provide corridors for the movement of wildlife and a place for native flora to flourish, without impacting on productivity. File Picture.
SUN, 20 JUN, 2021 – 17:00AOIFE WALSH
Thinking about the world outside of the field by managing its margins can have a very positive impact on nature and contribute to the improvement of biodiversity on Irish farms.
Field margins are important habitats and networks for nature and they provide corridors for the movement of wildlife and a place for native flora to flourish, without impacting on productivity.
Aoife Walsh, Teagasc, and UCD MAIS student highlights some of the key actions that farmers can take to ensure that field margins are retained, maintained, and enhanced for farmland biodiversity.
“Field margins are easy to manage strips of naturally growing vegetation that are found along the edge of fields beside linear features like hedgerows.
“Field margins are extremely valuable biodiversity habitats that are structurally different from what you might find in the centre of a ryegrass field.
“They are comprised of a variety of plants, including naturally growing wildflowers and grasses that produce flowers and seeds which benefit seed-eating birds like the House Sparrow, the Linnet and the Yellowhammer and pollinators like Bumblebees and solitary bees who avail of pollen and nectar from the margin’s flowering plants.
“Field margins facilitate the movement of wildlife throughout the farming landscape, acting as a highway for nature and providing cover for small mammals like shrews and voles, in turn providing owls with an ideal hunting ground.”
Field margins require some management in order to optimise them as habitats for biodiversity, Aoife adds.
Grazing
In grazing situations, field margins should be fenced off to exclude livestock. The area that is fenced can range in width with wider margins providing more room for biodiversity.
This action will further enhance the structural diversity of the margin by allowing vegetation to flower and go-to-seed.
“Margins should be cut in autumn after plants have flowered, at least once every three years, and this will prevent the vegetation within the margin becoming too rank or turning into scrub.”
Space
In addition, a minimum space of 1.5m between the main field crop and the base of the surrounding boundary should be maintained when spraying, cultivating, and applying fertiliser, urges Aoife.
“Increasing the width of field margins reduces the need for sprays as the space created will allow for a hedge cutter to mechanically control any encroachment.
“Blanket spraying under the wire should be avoided as this will lead to the removal of plant diversity. If chemically controlling noxious weeds (ragwort, thistle, docks, male wild hop, common barberry, and wild oats, as listed under the noxious weed act) targeted spot spraying should be practised.
“As is the case with spraying, cultivation also leads to the removal of field margin habitats.
“Maintaining a minimum distance of 1.5m out from the base of boundaries when cultivating will ensure that an area of margin remains undisturbed allowing the existing diversity to continue to flourish.
A new study published Tuesday by the academic journal Frontiers in Environmental Science finds that pesticides widely used in American agriculture pose a grave threat to organisms that are critical to healthy soil, biodiversity and soil carbon sequestration to fight climate change. Yet those harms are not considered by U.S. regulators.
The study, by researchers at the Center for Biological Diversity, Friends of the Earth U.S. and the University of Maryland, is the largest, most comprehensive review of the impacts of agricultural pesticides on soil organisms ever conducted.
The researchers compiled data from nearly 400 studies, finding that pesticides harmed beneficial, soil-dwelling invertebrates including earthworms, ants, beetles and ground nesting bees in 71% of cases reviewed.
“It’s extremely concerning that 71% of cases show pesticides significantly harm soil invertebrates,” said Dr. Tara Cornelisse, an entomologist at the Center and co-author of the study. “Our results add to the evidence that pesticides are contributing to widespread declines of insects, like beneficial predaceous beetles and pollinating solitary bees. These troubling findings add to the urgency of reining in pesticide use.”
The findings come on the heels of a recent study published in the journal Science showing pesticide toxicity has more than doubled for many invertebrates since 2005. Despite reduced overall use of insecticides, the chemicals most commonly used today, including neonicotinoids, are increasingly toxic to beneficial insects and other invertebrates. Pesticides can linger in the soil for years or decades after they are applied, continuing to harm soil health.
The reviewed studies showed impacts on soil organisms that ranged from increased mortality to reduced reproduction, growth, cellular functions and even reduced overall species diversity. Despite these known harms, the Environmental Protection Agency does not require soil organisms to be considered in any risk analysis of pesticides. What’s more, the EPA gravely underestimates the risk of pesticides to soil health by using a species that spends its entire life aboveground — the European honeybee — to estimate harm to all soil invertebrates.
“Below the surface of fields covered with monoculture crops of corn and soybeans, pesticides are destroying the very foundations of the web of life,” said Dr. Nathan Donley, another co-author and scientist at the Center. “Study after study indicates the unchecked use of pesticides across hundreds of millions of acres each year is poisoning the organisms critical to maintaining healthy soils. But our regulators have been ignoring the harm to these important ecosystems for decades.”
Soil invertebrates provide a variety of essential ecosystem benefits such as cycling nutrients that plants need to grow, decomposing dead plants and animals so that they can nourish new life, and regulating pests and diseases. They’re also critical for the process of carbon conversion. As the idea of “regenerative agriculture” and using soil as a carbon sponge to help fight climate change gains momentum around the world, the findings of this study confirm that reducing pesticide use is a key factor in protecting the invertebrate ecosystem engineers that play a critical role in carbon sequestration in the soil.
“Pesticide companies are continually trying to greenwash their products, arguing for the use of pesticides in ‘regenerative’ or ‘climate-smart’ agriculture,” said Dr. Kendra Klein, a co-author who’s also a senior scientist at Friends of the Earth. “This research shatters that notion and demonstrates that pesticide reduction must be a key part of combatting climate change in agriculture.”
“We know that farming practices such as cover cropping and composting build healthy soil ecosystems and reduce the need for pesticides in the first place,” said co-author Dr. Aditi Dubey of the University of Maryland. “However, our farm policies continue to prop up a pesticide-intensive food system. Our results highlight the need for policies that support farmers to adopt ecological farming methods that help biodiversity flourish both in the soil and above ground.”
Background
The review paper looked at 394 published papers on the effects of pesticides on non-target invertebrates that have egg, larval or immature development in the soil. That review encompassed 275 unique species or groups of soil organisms and 284 different pesticide active ingredients or unique mixtures of pesticides.
The assessment analyzed how pesticides affected the following endpoints: mortality, abundance, richness and diversity, behavior, biochemical markers, impairment of reproduction and growth, and structural changes to the organism. This resulted in an analysis of more than 2,800 separate “cases” for analysis, measured as a change in a specific endpoint following exposure of a specific organism to a specific pesticide. It found that 71% of cases showed negative effects.
Negative effects were evident in both lab and field studies, across all studied pesticide classes, and in a wide variety of soil organisms and endpoints. Organophosphate, neonicotinoid, pyrethroid and carbamate insecticides, amide/anilide herbicides and benzimidazole and inorganic fungicides harmed soil organisms in more than 70% of cases reviewed.
Insecticides caused the most harm to nontarget invertebrates, with studies showing around 80% of tested endpoints negatively affected in ground beetles, ground nesting solitary bees, parasitic wasps, millipedes, centipedes, earthworms and springtails.
Herbicides and fungicides were especially detrimental to earthworms, nematodes and springtails.
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