Gram Research analysis of a 2026 Pest Management Science study found that cotton bollworm caterpillars resistant to Bt toxins needed 2.20 to 9.53 times more toxin to be controlled than non-resistant caterpillars. Bt corn carrying multiple toxins worked better against these resistant insects than single-toxin corn.
Gram Research analysis of a 2026 study in Pest Management Science looked at whether cotton bollworm caterpillars that had been bred to resist Bt toxins could still be controlled by genetically modified corn. Bt corn makes a natural bacterial toxin that kills certain pests. The researchers found that resistant caterpillars were less affected by three Bt corn varieties than caterpillars that had never been exposed to the toxins. Corn carrying two or more toxins, called pyramided corn, worked better against the resistant insects than corn with a single toxin. The experiments were done in the laboratory, so the results cannot yet be applied directly to farm fields. Still, the findings point to why farmers and scientists need to rotate toxins and monitor pest resistance over time.
Key Statistics
A 2026 laboratory study published in Pest Management Science found that cotton bollworm caterpillars resistant to Cry2Ab needed 2.20 to 9.53 times more toxin to be controlled than non-resistant caterpillars.
A 2026 study in Pest Management Science reported that Cry1Ac-resistant cotton bollworm strains required 3.44 to 8.84 times more toxin than the susceptible comparison strain when fed Bt corn leaf material.
According to a 2026 Pest Management Science laboratory study, resistant caterpillars showed significantly lower death rates than non-resistant caterpillars when feeding on fresh Bt corn silk and kernels.
The Quick Take
- What they studied: Researchers asked whether caterpillars that had become resistant to certain Bt toxins in the lab could still be controlled by modern Bt corn varieties, and which corn designs worked best against them.
- Who participated: The participants were laboratory strains of cotton bollworm caterpillars, a major crop pest. Two strains had been bred to resist a toxin called Cry1Ac, two resisted Cry2Ab, and one unexposed strain served as the comparison. The exact number of caterpillars was not specified in the study summary.
- Key finding: Resistant caterpillars needed about 2.20 to 9.53 times more toxin to be controlled than the non-resistant strain, depending on the strain and corn variety. Corn carrying multiple toxins killed resistant caterpillars more effectively than corn with one toxin.
- What it means for you: For most people, this is a food-system and farming story rather than a personal health advice topic. It suggests that pest resistance is a real concern for Bt crops, and that using corn with several toxins may help slow resistance. Results come from lab tests, so real-world effects on farms are still unknown.
The Research Details
The researchers raised several groups of cotton bollworm caterpillars. Some groups had been selected in the lab over many generations to survive Bt toxins called Cry1Ac or Cry2Ab. A comparison group had never been exposed to these toxins. This design lets scientists see how much resistance changes an insect’s response to the same corn.
To test the corn, the team gave caterpillars three types of Bt corn: one with a single toxin, one with two toxins plus a third protein, and one with two toxins. They tested leaves, silk, and kernels. Leaf material was ground into powder and mixed into the caterpillars’ food, while fresh silk and kernels were offered directly. The team then measured how many caterpillars survived or grew normally.
After the caterpillars ate the corn, the researchers measured how active certain genes were in the insects’ gut lining. These genes make proteins that the toxins latch onto, so changes in them can affect how well the toxins work.
Controlled lab tests let scientists compare the same toxins and corn types under identical conditions. This makes it easier to see whether resistance is causing the drop in effectiveness, rather than other factors like weather or differences between fields. Measuring gene activity also gives clues about the biological mechanism behind resistance.
The study used clear comparison groups, multiple resistant strains, and several corn types, which strengthens confidence in the pattern. The authors were careful to say that the strains were lab-selected and that they did not directly test whether lower gene activity causes resistance. The exact number of insects was not stated in the summary, so readers cannot judge the statistical power from the information provided. Because this is a single laboratory study, it should be considered one piece of evidence rather than a final answer.
What the Results Show
Both the caterpillars resistant to Cry1Ac and those resistant to Cry2Ab were less affected by all three Bt corn varieties than the non-resistant comparison group. The researchers measured how much toxin was needed to stop half of the caterpillars from growing past a certain stage within seven days. Resistant strains needed 3.44 to 8.84 times more toxin for Cry1Ac and 2.20 to 9.53 times more for Cry2Ab, with one Cry2Ab strain showing even greater resistance on one corn variety.
Tests with fresh silk and kernels, the parts of corn that caterpillars actually eat in fields, confirmed the pattern. Resistant caterpillars died at lower rates than the comparison group when feeding on these tissues.
Corn with multiple toxins performed better. The two multi-toxin varieties killed resistant caterpillars more effectively than the single-toxin corn, and the advantage was greatest for strains with milder resistance. This suggests that stacking different toxins may help control insects that have partly adapted to one of them.
The team also found that several genes involved in moving toxins out of insect cells and in binding toxins to the gut lining were less active after eating Bt corn. The strongest changes were in ABCC2, which dropped in Cry1Ac-resistant strains, and in ABCC2 and ABCA2, which dropped in Cry2Ab-resistant strains. The authors noted these gene changes were linked to resistance but were not proven to cause it.
The study also examined genes such as ABCC3, APN1, and APN2, which were downregulated after Bt corn consumption. These changes add to the picture of how insects may adapt to toxins, though their exact roles remain unclear. The results suggest that resistance is not just one simple change but may involve several gene systems working together.
Earlier research has documented that cotton bollworm populations in China and elsewhere can develop resistance to Bt toxins, and that cross-resistance between related toxins can occur. This study adds detail by testing newer multi-toxin corn designs and linking resistance to changes in gut gene activity. It supports the general idea that using several toxins together can help manage resistance, though the lab setting limits how far these findings can be generalized.
The most important limitation is that the caterpillars were selected for resistance in the laboratory, not in fields. Real pest populations may behave differently. The study also did not directly prove that lower gene activity causes resistance, only that the two were associated. The sample size was not specified in the summary, and the results apply to particular corn varieties and toxin combinations used in China. Farm conditions such as weather, other pests, and planting practices were not part of the experiments.
The Bottom Line
Based on this lab study, researchers and farm managers may consider using multi-toxin Bt corn and rotating toxins to slow resistance in cotton bollworm. Confidence in these recommendations is moderate, since the pattern is consistent across several resistant strains and tissues but has not yet been tested in fields. Ongoing monitoring of pest populations is also suggested to catch resistance early.
Farmers who grow Bt corn, agricultural extension advisers, crop scientists, and regulators who oversee pest management programs should pay close attention. Most consumers do not need to change their habits based on this study. People interested in food and farming policy may find it useful as background.
Lab findings like these usually take several years to translate into farm guidance, because they must be confirmed in field trials and reviewed by agricultural agencies. Changes in pest management practices would likely appear over multiple growing seasons rather than immediately.
Frequently Asked Questions
Are caterpillars becoming resistant to Bt corn?
A 2026 laboratory study in Pest Management Science found that cotton bollworm caterpillars selected for resistance to Cry1Ac or Cry2Ab toxins were less affected by several Bt corn varieties. Resistance levels ranged from about 2.20 to 9.53 times higher, depending on the strain and corn type tested.
Which type of Bt corn works best against resistant caterpillars?
In the 2026 study, corn carrying multiple toxins, known as pyramided corn, killed resistant cotton bollworm caterpillars more effectively than single-toxin corn. The advantage was most noticeable in strains with lower levels of resistance, according to the researchers’ laboratory tests.
Does this study prove Bt corn is unsafe to eat?
This study examined crop pests and did not test effects on people. It focused on how insects respond to Bt corn toxins in the laboratory. Questions about food safety are addressed through separate regulatory reviews, which should be consulted for information on human health.
Can these lab results be applied to farm fields right away?
Not yet. The caterpillars were selected for resistance in the laboratory, so the results cannot be directly applied to farm fields. Field trials and continued monitoring of pest populations are needed before farming recommendations can be changed based on these findings.
Want to Apply This Research?
- If you grow crops or follow agricultural news, track which Bt corn varieties and toxin types you use each season, along with any noticeable pest damage in your fields. Record the percentage of plants showing damage by growing season to spot trends over time.
- Users who work in farming or gardening can log whether they rotate corn varieties or toxin types between seasons. Reviewing these records with local agricultural extension advice can help identify when a change in strategy may be worth discussing.
- Over the long term, keep a yearly log of pest counts, crop damage, and any changes in product recommendations from local agricultural advisers. Comparing these records year to year can reveal whether pest control is becoming less effective, which would be an early sign of resistance.
This article summarizes a laboratory study of insect pests and genetically modified corn. It is intended for general education about agricultural science and does not provide farming, food safety, or health advice. Results from controlled lab experiments may not apply to real-world fields. Farmers should consult local agricultural extension services, and people with questions about food safety should consult relevant regulatory agencies or qualified professionals.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.