Correlation of EPG waveforms from Lygus lineolaris feeding on cotton squares and chemical evidence of inducible tannins

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

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2017
Publication Date: 7/8/2017
Citation: Cervantes, F.A., Backus, E.A., Godfrey, L., Wallis, C.M., Akbar, W., Clark, T., Rojas, M.G. 2017. Correlation of EPG waveforms from Lygus lineolaris feeding on cotton squares and chemical evidence of inducible tannins. Annals of the Entomological Society of America. 110:2068-2075.

Interpretive Summary: Tarnished plant bug, Lygus lineolaris, is an important pest of cotton in the mid-southern United States. Cotton production is severely affected by direct damage inflicted to cotton squares caused by lygus bug feeding. Study of lygus bug feeding with AC-DC electropenetrography helped elucidate different interactions between the insect pest and the cotton plant and shed light on how lygus bug might overcome plant defenses. Correlation of specific behaviors, performed by lygus while feeding on a cotton square, with plant damage and plant response, was studied with the use of electropenetrography, histology, microscopy, and chemical analysis. Plant response to lygus feeding was observed as tannin production and accumulation in the cotton square, however such response was not sufficient to deter the insect from feeding. These results suggest that tannin detoxification compounds might be present in L. lineolaris saliva and provide new research avenues for scientists to continue studying the mechanisms of detoxification used by lygus to overcome plant defenses and to use this information for development of resistant varieties of cotton.

Technical Abstract: Probing behavior of Lygus lineolaris (Palisot de Beauvois), one of the most important pests affecting cotton production in mid-southern United States, has previously been characterized with electropenetrography (EPG). Cell rupturing (CR) and Ingestion (I) EPG waveforms were identified as two of the main stylet-probing behaviors by adult L. lineolaris. However, characterization and identification of EPG waveforms is not complete until specific events of a particular waveform are correlated to insect probing. With the use of a third generation AC-DC electropenetrograph, histology, microscopy, and chemical analysis, probing behavior of L. lineolaris on pin-head cotton squares was studied. Occurrences of waveforms CR and I were artificially terminated when observed during the EPG recording. Histological samples of probed pin-head cotton squares were prepared and analyzed to correlate specific types and occurrences of feeding damage location and plant responses to insect feeding. Both waveforms CR and I occurred in the staminal column of the cotton square. CR events by L. lineolaris elicited the production of dark-red deposits seen in histological staining that were demonstrated via chemical analysis to contain tannins, apparently secreted as a plant defense response. It is hypothesized that wounding and/or saliva secreted during CR triggered release of tannins, because tannin production is positively correlated with the number of CR events performed by L. lineolaris. Degraded plant tissue and tannins were removed from the staminal column during occurrence of waveform I. These results define CR and I as probing waveforms performed by L. lineolaris on pin-head cotton squares. These biological definitions will now allow EPG to be used to quantitatively compare L. lineolaris feeding among different plant treatments, with the goal of improving pest management tactics against this pest.