The State of Insect Resistance to Transgenic Bt Crops

Entomology Today 2 weeks ago 1 Comment

Cultivation of transgenic crops engineered to produce insecticidal proteins from Bacillus thuringiensis (Bt) has grown rapidly in the past 25 years. Bt crops have had noteworthy successes, but resistance to Bt crops has evolved in numerous instances. Five cases of practical resistance to Bt proteins that are produced by transgenic crops are documented for corn earworm (Helicoverpa zea), which is the most for any pest. (Photo by John C. French Sr., Retired, Universities:Auburn, GA, Clemson and U of MO, Bugwood.org)

By John P. Roche, Ph.D.

Insect pests damaging crops is a huge problem worldwide, threatening food security and causing significant economic loss. One avenue to address this is to genetically engineer crops to produce proteins from the bacterium Bacillus thuringiensis (Bt) that kill pests but are safe for most nontarget organisms. Although Bt-modified crops have been useful for controlling pests in numerous instances, some pests evolve resistance to Bt insecticide proteins. Therefore, scientists must evaluate the efficacy of Bt modified crops and find ways to delay evolution of insecticide resistance.

Sustained susceptibility to Bt cotton was essential for eradicating the pink bollworm (Pectinophora gossypiella) from the United States and Mexico, which it had invaded more than a century ago.As part of a multi-tactic program, pink bollworm caterpillars were mass reared (as shown here) and 11 billion sterile moths were released by airplanes to overwhelm its populations in the field. By contrast, this pest evolved resistance to dual-toxin Bt cotton in India, where it was used extensively with scarce non-Bt host plant refuges and limited integration of other tactics. (Photo by Alexander Yelich, University of Arizona)

In a review published in January in the Journal of Economic Entomology, Bruce Tabashnik, Ph.D., and Yves Carrière, Ph.D., of the University of Arizona and Jeffrey Fabrick, Ph.D., of the USDA Agricultural Research Service analyze both of these needs by examining patterns of Bt resistance in agricultural pests around the globe. The review is part of a special collection on field-evolved resistance to Bt crops.

The acreage of Bt-modified crops has grown rapidly in the past 20 years, with over a 100-fold increase between 1996 and 2019. The USDA estimates that, in the U.S. from 2009 to 2020, Bt crops accounted for more than 75 percent of the area planted with corn and cotton and that, from 2016 to 2020, 81 percent of corn and 87 percent of cotton planted in the U.S. was engineered to produce Bt proteins.

Bt crops have helped to suppress pests while also decreasing the need for conventional insecticides and augmenting the effectiveness of biological control species. “Two stunning successes of Bt crops against invasive pests in the United States,” Tabashnik says, “are suppression of the European corn borer (Ostrinia nubilalis) to its lowest levels in more than 75 years by Bt corn and eradication of the pink bollworm (Pectinophora gossypiella) using Bt cotton together with sterile moth releases and other tactics.” An example of a success against a native pest is the control of the tobacco budworm moth Chloridea virescens using Bt cotton in the U.S. and Mexico.

In their review, Tabashnik, Carrière, and Fabrick examined 73 sets of data on monitoring resistance to Bt crops, including information about responses to 10 Bt toxins in 22 species of moth and two species of beetle. They differentiated resistance found in these studies into the following three categories:

1. practical resistance, in which more than half of the individuals in a population are resistant and the field efficacy of the Bt crop has decreased;
2. early warning of resistance, in which resistance has evolved but fewer than half of individuals are resistant and efficacy of the Bt crop has not decreased;
3. no decrease in susceptibility, in which there is no statistically significant decrease observed in susceptibility.

In the 73 data sets examined, they found 26 cases of practical resistance. The average time from first planting of a particular Bt crop to the appearance of practical resistance was 6.6 years. Over half of the cases of practical resistance were in three species—the moths Helicoverpa zea and Spodoptera frugiperda and the beetle Diabrotica virgifera virgifera. Geographically, half of the instances of practical resistance were in the U.S. This makes sense, as the U.S. has planted Bt crops widely and extensively monitored resistance.

Tabashnik and colleagues found 17 instances of early warning of resistance. The mean time of detection of early warning of resistance was 8.6 years after exposure to Bt crops.

Thirty instances of no significant resistance were found after two to 24 years of exposure, with an average duration since exposure to Bt crops of 12.2 years.

The many instances of practical resistance lead to the question of how resistance can be delayed or prevented. One important way to reduce resistance is by creating refuges consisting of non-Bt-modified plants that serve as hosts for pest insects that are not resistant. Refuges were first envisioned to reduce evolution of resistance to insecticide sprays, but they have been crucial for slowing evolution of resistance to Bt insecticides. Because the refuge plants don’t produce Bt proteins, they allow survival of susceptible insects that can mate with any resistant insects that emerge from Bt crops.

Another factor that can hinder the evolution of resistance is increasing the concentration of Bt proteins enough to kill insects that are heterozygous for resistance, i.e., they carry only one allele that confers resistance. This “high-dose” strategy makes the resistance functionally recessive and less likely to spread quickly.

Tabashnik says, “Theory and empirical evidence indicate that recessive inheritance of pest resistance to Bt crops and abundant refuges of non-Bt host plants can help to sustain the efficacy of Bt crops. When inheritance of resistance is not recessive, the abundance of refuges relative to Bt crops can be increased to effectively delay evolution of resistance.”

Strategies being explored to heighten the efficacy of Bt crops include targeting each pest with two or more Bt proteins and using Bt proteins together with RNA interference (RNAi) insecticides. In the close of their review, Tabashnik and colleagues emphasize that rather than relying on any one control tactic—such as transgenic crops—sustainable pest suppression combines diverse integrated pest management tools.

Read More

“Global Patterns of Insect Resistance to Transgenic Bt Crops: The First 25 Years”

Special Collection: Global Perspectives on Field-Evolved Resistance to Transgenic Bt Crops

Journal of Economic Entomology

John P. Roche, Ph.D., is an author, biologist, and science writer with a Ph.D. in the biological sciences and a dedication to making rigorous science clear and accessible. He writes books and articles, and provides writing for universities, scientific societies, and publishers. Professional experience includes serving as a scientist and scientific writer at Indiana University, Boston College, and the University of Massachusetts Medical School, and as editor-in-chief of science periodicals at Indiana University and Boston College.

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Agriculture, Specials

The profitability of planting transgenic eggplants

Published February 3, 2023, 5:00 PM

by Manila Bulletin Agriculture

By Henrylito D. Tacio

The eggplant is used in various cuisines around the world. It can be sliced, battered, and deep-fried, and then served with various sauces.  It can also be stuffed with meat, rice, or other fillings and then baked. In the Philippines, eggplant is one of the main ingredients of pinakbet, torta, sinigang, ensalada, and kare-kare.   

The popularity of eggplant is the reason why it is the number one vegetable in the country – in terms of area planted (20,000 hectares) and volume of production (179,000 metric tons).  Most of the top producing regions are located in Luzon like Ilocos, Central Luzon, Cagayan Valley, CALABARZON (composed of Cavite, Laguna, Batangas, Rizal, and Quezon) and Bicol.

Resource-poor farmers in many provinces grow eggplant and depend on it for their livelihood. One of them is Edgar C. Talasan, a vegetable farmer from barangay Imalutao in Impasug-ong, Bukidnon. At one time, he planted 2,500 eggplants in his farm. In just one crop cycle, he got a gross income of P84,000. 

From the income of his farm, he was able to raise his family well. In fact, he sent his daughter through college by selling the vegetables harvested from his farm. “I was happy and content in my little kingdom,” he said.

But what makes him sad is the fact that eggplant production in the country suffers a severe yield loss from insect pests, diseases and extreme environmental conditions. In a technology forum he attended in Pangasinan, he realized that eggplant growers sprayed their crops with chemicals once a day to protect the eggplants from infestation. 

Destructive eggplant pest

The most destructive insect pest that attacks the crop is called the eggplant fruit and shoot borer (EFSB). Scientifically, it is called Leucinodes orbonalis, a moth species prevalent in Asia and Africa. The moths’ larvae feed on eggplant shoots and fruits until maturity. 

“The EFSB can cause as much as 50-75 percent loss of fruits,” said former Science Secretary Emil Q. Javier. “The worm of the insect bore tunnels in the fruit, rendering them unfit for consumption.”

Unfortunately, there is no known genetic resistance to EFSB in cultivated and wild eggplants.  “The insects are concealed in the shoots and fruits and are difficult to reach,” Dr. Javier explained. 

To reduce the population of EFSB, some farmers practice integrated pest management, which include: regular crop rotation, or intercropping eggplant with other vegetables; removal and burying of infested and damaged shoots and fruits; and using nylon net barriers to protect plants from the insects. 

Other farmers employ the following: using light or pheromone traps; growing eggplants in a screen house before transplanting in their farms; and conservation of beneficial arthropods (spiders, parasitoids, and predators). 

Using pesticides 

But there are farmers who spray their eggplants almost every other day with insecticides to protect the crops. 

In his 15 years of vegetable farming, Talasan said that in every eggplant cropping cycle, he sprayed at least twice a week. For every 1,000 eggplant hills, he used 0.5 kilogram of Lannate, two bottles (250 mL) of Prevathon, two bottles (250 mL) of Alika, one liter of Karate, one kilogram of Daconil, and 0.5 liter of Selecron. 

The current method of spraying chemicals to eggplants in order to control EFSB is unacceptable, according to Dr. Emiliana Bernardo, an entomologist or a scientist who studies insects. 

The practice is also unhealthy to consumers, farmers, and the environment, said Dr. Bernardo, who is also a member of the Institutional Biosafety Committee of the University of the Philippines Los Baños.

She said studies conducted in major eggplant producing provinces found that almost all farmers use chemical insecticides and that some even dip the unharvested eggplant fruits in a mix of chemicals just to ensure that harvests are marketable. 

“The very basic question is, which is safer, the present practice or the alternative, the Bt eggplant which is rigorously evaluated by experts?” she asked. “Is bathing the unharvested eggplant fruits in chemicals, which would end up in people’s dinner tables, safe?” 

Bt eggplant

 Are there other ways of controlling EFSB?  Scientists who tried various methods came up with Bt eggplant, a genetically modified (GM) crop. Bt stands for Bacillus thuringiensis. 

 “Bt talong was developed by genetically engineering a gene from the bacteria so that the genetically modified eggplants now produce a protein that defends it against insect attacks,” explained Dr. Michael Purugganan, a Filipino plant geneticist who is the Dean of Science at the New York University.

“When ingested by the larvae of the target insect, the Bt protein is activated in the gut’s alkaline condition and punctures the mid-gut leaving the insect unable to eat. The insect dies within a few days,” noted a briefing paper circulated by the Laguna-based International Service for the Acquisition of Agri-biotech Applications (ISAAA). 

Bt is present in the Philippine soil and has been in use for years without any harmful effects. As it comes from the earth itself, Bt is very natural, according to Dr. Bernardo. In 1901, Bt was discovered to have an insecticidal property. By the 1950s, it became a well-known biological insecticide. 

“Bt is easily cultured by fermentation,” the ISAAA briefing paper said. “Thus, over the last 40 years, Bt has been used as an insecticide by farmers worldwide. Organic farming has benefited from Bt insecticide, as it is one of the very few pesticides permitted by organic standards. The insecticide is applied either as a spray or as ground applications. It comes in both granules and liquefied form.”

The first Bt eggplant was developed by the Indian Maharashtra Hybrid Seeds Company Limited (Mahyco).  The Institute of Plant Breeding at the University of the Philippines at Los Baños (UPLB) has developed the Bt eggplant in the country, in partnership with Mahyco and Cornell University and with support from the United States Agency for International Development (USAID). 

The ISAAA says that before Bt eggplant is approved for commercial use, scientists and regulators ensure that it passes through many tests and safety assessments.  In the Philippines, the biosafety of Bt crops is evaluated by a pool of technical scientists in five stages: contained research in laboratories and screen houses; small limited confined field trials; multi-location field trials; food, feed and processing; and commercial propagation. 

Approved for propagation 

In July 2021, the Bureau of Plant Industry (BPI) – a line agency of the Department of Agriculture – approved Bt eggplant for direct use as food, feed and for processing (FFP).  In issuing Biosafety Permit No. 21-078FFP, it is found “to be safe as conventional eggplant” and “can substitute for its traditional counterpart.” 

A year later, on October 18, 2022, the government approved Bt eggplant as the third genetically engineered crop for commercial propagation, following Bt corn and golden rice (now known as Malusog rice).  

Bt eggplant’s approved followed regulatory procedures as detailed in the revised Joint Department Circular, which showed proof of the country’s commitment to science and improvements in biotechnology. 

Vegetable farmers need not to worry when it comes to planting eggplant.  “There are no differences in the production practices (fertilizer application, weeding, irrigation) used in growing of Bt eggplant compared to conventional eggplant except in insecticide application against the borer,” said Dr. Lourdes D. Taylo, study leader of the Bt eggplant project from UPLB. 

Economic and health benefits

A recent study showed that Bt eggplant could bring health cost savings of P9.33 million yearly from its nearly pesticide-free use. Researcher Sergio R. Francisco has estimated savings in a survey of long exposure to pesticide spraying against the highly-infested EFSB in his study, “Health and Environmental Impacts of Bt Eggplant.” 

The study was based on the perception of 100 eggplant farmers from Batangas, Nueva Ecija, Pangasinan, and Quezon who sprayed their eggplant. These farmers have a long experience in farming – from 9.96 to 18.04 years. 

Another study showed that a Bt eggplant farmer gets P50,330.00 net income for every P100,000.00 gross sales. In comparison, a net income of P16,880.00 is all a farmer gets who plant conventional varieties. 

In a press statement, it was disclosed that the benefit to human health from health cost savings in growing Bt eggplant is equivalent to P2.49 million yearly as risk from illnesses is avoided. For farm animals, the projected benefit per year is at P2.12 million. 

For beneficial insects, the environmental benefit is valued at P2.45 million yearly and for bird species, P2.27 million – as these are saved from death, thereby contributing to biodiversity enhancement.  

Are Bt crops like Bt eggplant safe to eat? The GM Science Review Panel of the United Kingdom has this to say: “For human health, to date there is no evidence currently commercialized GM crop varieties or foods made from them, are toxic, allergenic or nutritionally deleterious.  On balance, we conclude that the risks to human health are very low for GM crops currently on the market.” 

The Geneva-based World Health Organization also assured: “The potential direct health effects of GM foods are generally comparable to the known risks associated with conventional foods, and include, for example, the potential for allergenicity and toxicity of components present, and the nutritional quality and microbiological safety of the food.”

Photos by Henrylito D. Tacio
Additional photos by SEARCA

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GM/Biotech Crops Report – August 2022

1st August 2022

• GM/Biotech Crops Monthly Reports (BELOW) form part of BCPC’s free three-tier Biotech Crops Info service.
• This service also includes a weekly round-up of news from around the globe – see BCPC Newslink GM Crops section.
• Plus – Free access database on over 300 GM/biotech products covering 23 crops in the global market visit BCPC’s GM/Biotech Crops Manual – Register here for free access.
• Already registered? Click here

GM/Biotech Crops Monthly Report August 2022

More accurate gene editing

CRISPR-Cas9 editing can cause off target edits and cuts both strands of the DNA helix at once. Now a system related to CRISPR but cutting only one strand of the DNA promises new options and greater accuracy in the edits.
Full Story.

Boost to rice yields

Over-expression of a single gene in rice seems to shorten the time taken for the plant to mature, improve nitrogen efficiency and boost yields by up to 40%.
Full Story.

Improved efficiency in food production

Photosynthesis is not the only way to produce food. Capturing the sun’s energy via photo-voltaic cells and using this energy to power an electrolyser that converts water and CO2 into acetate which can be utilised by mushrooms, yeasts and algae can be more efficient than growing crops. It sounds like an ideal food production system for space stations but here on earth there may be more resistance to this production method.
Full Story

Pod-borer resistance in chickpea

Gram pod borers account for a yield loss of 40-50% in chickpeas grown in India but a successful gene modification is achieving significant reductions in larval feeding damage.
Full Story

Australia starts to evaluate GM sorghum

Queensland University has been granted a licence to conduct field evaluations of GM sorghum over the next 3 years but the crop will not (yet?) be used for human or animal feed.
Full Story

Photosynthesis in overdrive

The University of Wisconsin have identified one of the brakes on photosynthesis and switched it off. The modified Arabidopsis plants produce greater quantities of aromatic compounds and, in doing so, absorb greater quantities of CO2.
Full story

Optimising wheat production

A study by Rothamsted has indicated that, if the genetics of wheat crops were optimised for the regions that the crop was grown in, growers could double their yields. However, a recent ‘Countryfile’ programme on the BBC reported a similar yield benefit achieved by a Ukrainian farmer who swapped his Russian-made combine harvester for a John Deere! Perhaps more widespread access to optimised harvest machinery could also improve harvested yields.
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This is rocket-science

By engineering the genome of soil bacteria, scientists have caused them to produce polycyclopropanated fatty acids that are sufficiently energy dense to be used as biofuels for road, shipping, aviation and rocket fuel. Let’s hope they can scale up production soon.
Full Story

Cassava Mosaic disease resistance

Cassava is a root crop that can grow in dry conditions without applied fertiliser and is a staple of many in India and Africa. Mosaic disease causes significant yield losses and the natural resistance of some landraces is easily lost during propagation. Now the gene involved has been identified, progress can be made on a more durable resistance:
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Improved immunity

Many plant pathogens switch off the plant’s immune response before they attack and now a team of scientists from Germany, France and Switzerland have decoded the signals that the pathogen uses to achieve this. They have also developed chemicals that re-activate the plant’s immune system in the lab and now they need to evaluate it in the field.
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Chitin for leaf blight control in rice

Chitin can be used as an insecticide due to the physical damage that it can cause to insect cuticles but now Chinese scientists have bio-engineered chitosan-iron nanocomposites that seem to have efficacy against bacterial leaf blight in rice.
Full Story

Wheat stripe rust resistance

The Sainsbury Laboratory has identified the genes that stop wheat rust infecting barley and now that the genes involved are known, it will allow this resistance to be transferred to other varieties:
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Phosphate biosensor

Many plants rely on soil fungi to scavenge for their phosphorus and reward the fungi with carbon compounds when they deliver the phosphates. Now a team at Texas University has developed a biosensor that allows them to monitor this trade and by optimising he process, they hope to make phosphate use by plants more efficient.
Full Story

Asian soybean rust resistance

Corteva and the 2blades Foundation based at the Sainsbury Laboratory have developed a durable rust resistance for soybeans, important because the yield losses caused by the disease can range 10 – 80%.
Full Story

Reduced pre-harvest sprouting in rice

Scientists at the Nanjing Agricultural University have used CRISPR-Cas0 to knock out various versions of the CsABA8ox gene to increase seed dormancy in rice. This makes pre-harvest sprouting less likely but they do not say if it affects the germination of a seed crop.
Full Story

THE LATEST ADDITIONS TO THE  GM/BIOTECH DATABASE ARE:

The latest approvals of biotech crops to report this month:

• HB4 wheat with improved drought tolerance approved for food and feed use in Argentina, Australia, Brazil, Columbia, New Zealand, Nigeria and the USA.

FOR INSTANT ACCESS TO GM BIOTECH MANUAL CLICK HERE (Registration required)

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