Entomologists issue warning about effects of climate change on insects

by University of Maryland

<img src="https://scx1.b-cdn.net/csz/news/800a/2022/entomologists-issue-wa-1.jpg&quot; alt="Entomologists issue warning about effects of climate change on insects" title="Climate change impacts on insects can be categorized into two major categories: Gradual long-term change and extreme events that will increase in frequency and severity, while interventions include formal mitigation of change through policy and public approaches which in turn help to reduce impacts in various ways. Credit: <i>Ecological Monographs

In a new scientific review, a team of 70 scientists from 19 countries warned that if no steps are taken to shield insects from the consequences of climate change, it will “drastically reduce our ability to build a sustainable future based on healthy, functional ecosystems.”

Citing research from around the world, the team painted a bleak picture of the short- and long-term effects of climate change on insects, many of which have been in a state of decline for decades. Global warming and extreme weather events are already threatening some insects with extinction—and it will only get worse if current trends continue, scientists say. Some insects will be forced to move to cooler climes to survive, while others will face impacts to their fertility, life cycle and interactions with other species.

Such drastic disruptions to ecosystems could ultimately come back to bite people, explained Anahí Espíndola, an assistant professor of entomology at the University of Maryland and one of the paper’s co-authors.

“We need to realize, as humans, that we are one species out of millions of species, and there’s no reason for us to assume that we’re never going to go extinct,” Espíndola said. “These changes to insects can affect our species in pretty drastic ways.”

Insects play a central role in ecosystems by recycling nutrients and nourishing other organisms further up the food chain, including humans. In addition, much of the world’s food supply depends on pollinators like bees and butterflies, and healthy ecosystems help keep the number of pests and disease-carrying insects in check.

These are just a few of the ecosystem services that could be compromised by climate change, the team of scientists cautioned. Unlike mammals, many insects are ectotherms, which means they are unable to regulate their own body temperature. Because they are so dependent on external conditions, they may respond to climate change more acutely than other animals.

One way that insects cope with climate change is by shifting their range, or permanently relocating to places with lower temperatures. According to one study cited by Espíndola and other scientists, the ranges of nearly half of all insect species will diminish by 50% or more if the planet heats up 3.2°C. If warming is limited to 1.5°C—the goal of the global Paris Agreement on climate change—the ranges of 6% of insects will be affected.

Espíndola, who studies the ways in which species respond to environmental changes over time, contributed to the sections of the paper that address range shifts. She explained that drastic changes to a species’ range can jeopardize their genetic diversity, potentially hampering their ability to adapt and survive.

On the other hand, climate change may make some insects more pervasive—to the detriment of human health and agriculture. Global warming is expected to expand the geographical range of some disease vectors (such as mosquitoes) and crop-eating pests.

“Many pests are actually pretty generalist, so that means they are able to feed on many different types of plants,” Espíndola said. “And those are the insects that—based on the data—seem to be the least negatively affected by climate change.”

The team noted that the effects of climate change are often compounded by other human-caused impacts, such as habitat loss, pollution and the introduction of invasive species. Combined, these stressors make it more difficult for insects to adapt to changes in their environment.

Though these effects are already being felt by insects, it is not too late to take action. The paper outlined steps that policymakers and the public can take to protect insects and their habitats. Scientists recommended “transformative action” in six areas: phasing out fossil fuels, curbing air pollutants, restoring and permanently protecting ecosystems, promoting mostly plant-based diets, moving towards a circular economy and stabilizing the global human population.

The paper’s lead author, Jeffrey Harvey of the Netherlands Institute of Ecology (NIOO-KNAW) and Vrije Universiteit Amsterdam, said in a statement that urgent action is needed to protect insects and the ecosystems they support.

“Insects are tough little critters, and we should be relieved that there is still room to correct our mistakes,” Harvey said. “We really need to enact policies to stabilize the global climate. In the meantime, at both government and individual levels, we can all pitch in and make urban and rural landscapes more insect-friendly.”

The paper suggested ways that individuals can help, including managing public, private or urban gardens and other green spaces in a more ecologically-friendly way—for instance, incorporating native plants into the mix and avoiding pesticides and significant changes in land usage when possible.

Espíndola also stressed the value of encouraging neighbors, friends and family to take similar steps, explaining that it’s an easy yet effective way to amplify one’s impact.

“It is true that these small actions are very powerful,” Espíndola said. “They are even more powerful when they are not isolated.”

Their paper was published in Ecological Monographs.

More information: Jeffrey A. Harvey et al, Scientists’ warning on climate change and insects, Ecological Monographs (2022). DOI: 10.1002/ecm.1553

Provided by University of Maryland 

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Insects have a weak capacity to adjust their critical thermal limits. Sam England, Author provided (no reuse)

Insects will struggle to keep pace with global temperature rise – which could be bad news for humans

Published: October 3, 2022 11.01am EDT

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1. Hester WeavingPhD Candidate in Entomology, University of Bristol

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Hester Weaving receives funding from a BBSRC studentship.

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Animals can only endure temperatures within a given range. The upper and lower temperatures of this range are called its critical thermal limits. As these limits are exceeded, an animal must either adjust or migrate to a cooler climate.

However, temperatures are rising across the world at a rapid pace. The record-breaking heatwaves experienced across Europe this summer are indicative of this. Heatwaves such as these can cause temperatures to regularly surpass critical thermal limits, endangering many species.

In a new study, my colleagues and I assessed how well 102 species of insect can adjust their critical thermal limits to survive temperature extremes. We found that insects have a weak capacity to do so, making them particularly vulnerable to climate change.

The impact of climate change on insects could have profound consequences for human life. Many insect species serve important ecological functions while the movement of others can disrupt the balance of ecosystems.

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How do animals adjust to temperature extremes?

An animal can extend its critical thermal limits through either acclimation or adaptation.

Acclimation occurs within an animal’s lifetime (often within hours). It’s the process by which previous exposure helps give an animal or insect protection against later environmental stress. Humans acclimate to intense UV exposure through gradual tanning which later protects skin against harmful UV rays.

One way insects acclimate is by producing heat shock proteins in response to heat exposure. This prevents cells dying under temperature extremes.

Some insects can also use colour to acclimate. Ladybirds that develop in warm environments emerge from the pupal stage with less spots than insects that develop in the cold. As darker spots absorb heat, having fewer spots keeps the insect cooler.

Adaptation occurs when useful genes are passed through generations via evolution. There are multiple examples of animals evolving in response to climate change.

Over the past 150 years, some Australian parrot species such as gang-gang cockatoos and red-rumped parrots have evolved larger beaks. As a greater quantity of blood can be diverted to a larger beak, more heat can be lost into the surrounding environment.

But evolution occurs over a longer period than acclimation and may not allow critical thermal limits to adjust in line with the current pace of global temperature rise. Upper thermal limits are particularly slow to evolve, which may be due to the large genetic changes required for greater heat tolerance.

Research into how acclimation might help animals survive exceptional temperature rise has therefore become an area of growing scientific interest.

A weak ability to adjust to temperature extremes

When exposed to a 1℃ change in temperature, we found that insects could only modify their upper thermal limit by around 10% and their lower limit by around 15% on average. In comparison, a separate study found that fish and crustaceans could modify their limits by around 30%.

But we found that there are windows during development where an insect has a greater tolerance towards heat. As juvenile insects are less mobile than adults, they are less able to use their behaviour to modify their temperature. A caterpillar in its cocoon stage, for example, cannot move into the shade to escape the heat.

Exposed to greater temperature variations, this immobile life stage has faced strong evolutionary pressure to develop mechanisms to withstand temperature stress. Juvenile insects generally had a greater capacity for acclimating to rising temperatures than adult insects. Juveniles were able to modify their upper thermal limit by 11% on average, compared to 7% for adults.

But given that their capacity to acclimate is still relatively weak and may fall as an insect leaves this life stage, the impact is likely to be limited for adjusting to future climate change.

What does this mean for the future?

A weak ability to adjust to higher temperatures will mean many insects will need to migrate to cooler climates in order to survive. The movement of insects into new environments could upset the delicate balance of ecosystems.

Insect pests account for the loss of 40% of global crop production. As their geographical distribution changes, pests could further threaten food security. A UN report from 2021 concluded that fall armyworm populations, which feed on crops such as maize, have already expanded their range due to climate change.

Insect migration may also carry profound impacts on human health. Many of the major diseases affecting humans, including malaria, are transmitted by insects. The movement of insects over time increases the possibility of introducing infectious diseases to higher latitudes.

There have been over 770 cases of West Nile virus recorded in Europe this year. Italy’s Veneto region, where the majority of the cases originate, has emerged as an ideal habitat for Culex mosquitoes, which can host and transmit the virus. Earlier this year, scientists found that the number of mosquitoes in the region had increased by 27%.

Insect species incapable of migrating may also become extinct. This is of concern because many insects perform important ecological functions. Three quarters of the crops produced globally are fertilised by pollinators. Their loss could cause a sharp reduction in global food production.

The vulnerability of insects to temperature extremes means that we face an uncertain and worrying future if we cannot curb the pace of climate change. A clear way of protecting these species is to slow the pace of climate change by reducing fossil fuel consumption. On a smaller scale, the creation of shady habitats, which contain cooler microclimates, could provide essential respite for insects facing rising temperatures.

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