Novel mechanism of thrips suppression by Cry51Aa2.834_16 Bt toxin expressed in cotton

Abstract

BACKGROUND Genetically engineered (GE) crops that express insecticidal traits have improved the sustainability of insect pest management worldwide, but many important pest orders are not controlled by commercially available toxins. Development of the first transgenic thysanopteran‐ and hemipteran‐active Bacillus thuringiensis (Bt) Cry51Aa2.834_16 toxin expressed in MON 88702 cotton will significantly expand the diversity of pests controlled in the crop. Here, we examined MON 88702 cotton activity against two thrips species within the same genera, Frankliniella fusca and Frankliniella occidentalis. We used a multi‐component cotton tissue assay approach to understand effects on adult longevity, fecundity, and larval development. RESULTS We found that in no‐choice assays, cotton plants expressing MON 88702 suppress oviposition, when compared to a non‐Bt cotton. MON 88702 did not kill a large proportion of F. fusca larvae or adults but killed most F. occidentalis larvae. Time series experiments with F. occidentalis larvae documented significant developmental lags for MON 88702 exposed individuals. We also found that female thrips preferred to oviposit on non‐Bt cotton when provided a choice. CONCLUSION Together these results describe the activity of MON 88702 against thrips. They document clear differences in toxin performance between different thrips species and throughout the insects' life cycle. Most importantly, we show that MON 88702 was associated with reduced oviposition via behavioral avoidance to the toxin. This is a novel mechanism of action for pest control for a Bt crop plant. Together, these results provide a basis to describe the mechanism of population control for MON 88702 cotton. © 2019 Society of Chemical Industry

Understanding the potential impact of continued seed treatment use for resistance management in Cry51Aa2.834_16 Bt cotton against Frankliniella fusca

“…However, the mechanism of MON 88702 activity creates added challenges to resistance management in the field. Specifically, recent studies have shown that MON 88702 acts by a non-lethal antixenosis leading to suppressed oviposition that results in fewer F. fusca larvae developing on MON 88702 cotton [13][14][15][16]. Similar non-lethal suppression of oviposition by adult F. fusca in conjunction with acute larval toxicity have been documented for neonicotinoid seed treated (NST) cotton [17][18][19].…”

“…Both MON 88702 cotton and neonicotinoid seed treatments have strong antixenotic effects on adult F. fusca resulting in large reductions in oviposition and larval establishment on cotton, even in the presence of alternative host plants. While MON 88702 alters feeding behavior and reduces oviposition of adults, it has minimal impacts on adult and larval survival [13][14][15][16]. Both imidacloprid and thiamethoxam applied as seed treatments also have minimal impact on survival of adult F. fusca and dramatically reduce oviposition on treated cotton seedlings; however, they also cause moderate to high levels of larval mortality [17][18][19].…”

Feeding behavior of Frankliniella fusca on seedling cotton expressing Cry51Aa2.834_16 Bt toxin

“…9,10 In no-choice experiments, they oviposited less on MON 88702 than on non-Bt cotton. 10,11 A previous study of L. lineolaris feeding behavior on MON 88702 showed antifeedant activity, wherein L. lineolaris tended to spend more time engaged in pre-oral digestion activity (i.e. cell rupturing by enzymatic, macerating saliva) and exhibited shorter periods of ingestion relative to insects that fed on non-Bt cotton.…”

“…[7][8][9][10][11] Although the spectrum of MON 88702 activity is unique, recent evidence suggests that the mechanism of population control involves a combination of lethal and non-lethal effects. 10 In choice experiments, adult female F. fusca avoided MON 88702 plants and ultimately settled and oviposited on non-Bt cotton. 9,10 In no-choice experiments, they oviposited less on MON 88702 than on non-Bt cotton.…”

“…10 In choice experiments, adult female F. fusca avoided MON 88702 plants and ultimately settled and oviposited on non-Bt cotton. 9,10 In no-choice experiments, they oviposited less on MON 88702 than on non-Bt cotton. 10,11 A previous study of L. lineolaris feeding behavior on MON 88702 showed antifeedant activity, wherein L. lineolaris tended to spend more time engaged in pre-oral digestion activity (i.e.…”