Quantitative differences in feeding behavior of 3rd instar nymphal Lygus lineolaris (Hemiptera: Miridae) occur on transgenic Bt cotton compared with non-Bt cotton

Authors: Cervantes, Felix; Backus, Elaine; GODFREY, L - University Of California, Davis; AKBAR, W - Monsanto Company; CLARK, T.L. - Monsanto Company; Rojas, Maria - Guadalupe

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2019
Publication Date: 2/25/2019
Citation: Cervantes, F.A., Backus, E.A., Godfrey, L., Akbar, W., Clark, T., Rojas, M.G. 2019. Quantitative differences in feeding behavior of 3rd instar nymphal Lygus lineolaris (Hemiptera: Miridae) occur on transgenic Bt cotton compared with non-Bt cotton. Journal of Economic Entomology. 112(4):1920-1925. https://doi.org/10.1093/jee/toz054.
DOI: https://doi.org/10.1093/jee/toz054

Interpretive Summary: Cotton production in the mid-southern United States is severely affected by direct damage to cotton squares during feeding by the tarnished plant bug, Lygus lineolaris, especially immature, nymphal life stages. Cotton plants carrying the protein Cry51Aa2. 834_16 derived from a soil-dwelling microbe, Bacillus thuringiensis (Bt), were recently shown to have long-exposure insecticidal effects on nymphs of L. lineolaris. However, development of lygus-resistant varieties of crops depends upon more than just killing the insects, but also upon changing the types and amounts of short-term feeding performed on cotton. One of the most important tools for studying insect feeding is electropenetrography (EPG), in which an electrical signal is applied to a plant on which a gold wire-tethered insect is feeding. The present study compared feeding behavior of nymphal L. lineolaris on pin-head cotton squares of non-Bt vs. Bt plants using AC-DC EPG. Overall, insects performed the same types of behaviors on both non-Bt and Bt-cotton squares. However,differences in numbers and duration of behaviors were observed between treatments. Nymphs on cotton increased their testing/tasting behaviors, made more frequent events of salivation, and decreased ingestion, supporting that Bt cotton plants were less palatable and/or digestible to L. lineolaris nymphs than non-Bt cotton. Results show that Bt cotton can productively contribute to an integrated pest management program for lygus bugs in cotton.

Technical Abstract: Lygus lineolaris is one the most important insect pests affecting cotton production in the mid-southern U.S.A. Bt-expressing cotton plants carrying the crystal protein Cry51Aa2.834_16 (designated MON 88702) were recently shown to have insecticidal effects on L. lineolaris. Although long exposures to constitutively expressed Bt toxin causes lygus adult and nymphal mortality, specific effects of the Cry51Aa2 protein on the feeding mechanisms of lygus bugs during short exposures was unknown until the present work. The most rigorous way to study these feeding mechanisms is with the use of AC-DC electropenetrography (EPG). The present EPG study is the first to examine effects of a Bt crop on heteropteran feeding. It compared feeding behavior of 3rd-instar nymphal L. lineolaris on pin-head cotton squares of non-Bt vs. Bt plants using AC-DC EPG. Waveforms were categorized and quantified based on stereotypical patterns previously reported. Overall, insects performed the same waveforms/ behaviors on both non-Bt and Bt-cotton plants, thus cell rupturing (CR; maceration of tissues), transition behavior (T; putative tasting and testing of tissues), and ingestion (I). However, quantitative differences in numbers and duration of behaviors were observed between treatments. Relative to nymphs on non-Bt cotton, those on Bt cotton spent more time overall in stylet probing, due to increased number of CR events per probe and longer durations of transition behavior, per event, per probe, and overall per insect. Despite longer durations of probing, ingestion events were shorter. When combined, increased testing/tasting, more frequent cell rupturing, and decreased ingestion supports that Bt cotton plants were less palatable and/or pre-orally digestible to L. lineolaris nymphs than non-Bt cotton, a potential mechanism of antixenosis. These results increase our understanding of the mechanisms that produce mortality of L. lineolaris nymphs on Bt-expressing cotton plants.