Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Entomology, Plant Pathology and Nematology

Major Professor

Scott D. Stewart

Committee Members

Eric Blinka, Jerome Grant, Tyson Raper


Field experiments done in 2016 and 2017 in Tennessee evaluated the effects of a Bt toxin, Cry51Aa2.834_16, on the management of thrips (Thysanoptera: Thripidae) and tarnished plant bug (TPB), Lygus lineolaris (Palisot De Beauvois), in cotton. For thrips, the Bt trait was as good or better than an insecticide-based approach. The Bt trait reduced numbers of immature TPB and provided partial plant protection from TPB injury. The Bt cotton had greater yields than non-Bt cotton when insecticides were not used. The Bt cotton required fewer insecticide applications to provide adequate plant protection from TPB than the non-Bt cotton. Current treatment thresholds for TPB performed similarly for Bt and non-Bt cotton. Insecticide applications for TPB increased fiber quality, while the Bt trait had minor effects.Other experiments done in 2016 and 2017 evaluated the behavioral response of thrips and TPB to Bt Cry51Aa2.834_16. Adult thrips avoided Bt cotton in field choice tests and in a test of cotton not treated with insecticides. In a greenhouse choice test more adult thrips and eggs were found on non-Bt cotton than Bt cotton. Similarly, in a field test of Bt and non-Bt cotton not treated with insecticides, 68% of adult thrips were collected on non-Bt cotton. The Bt trait did not affect the distribution of TPB within the canopy of cotton not sprayed with insecticides, although more square and flower injury was caused by TPB in non-Bt cotton. Adult TPB avoided diet containing Bt leaves and excised Bt squares in choice tests with non-Bt squares.Field experiments were conducted in 2017 and 2018 in Tennessee to determine if an image analysis tool, Canopeo (Oklahoma State University, Stillwater, OK), can be used to supplement current methods to estimate cotton seedling health in small-plot research. Small plot replicated tests analyzed showed a range of cotton seedling health. Cotton seedlings were visually rated for vigor and thrips injury and above ground biomass samples were also taken. A photograph of the center two rows of each plot was taken using Canopeo. Strong correlations were observed for Canopeo and biomass, Canopeo and vigor, and thrips injury ratings and biomass.


A version of this chapter was originally published by Scott H. Graham and Scott D. Stewart: Graham, S.H. and S.D. Stewart. 2018. Field study investigating Cry51Aa2.834_16 in cotton for control of thrips (Thysanoptera: Thripidae) and tarnished plant bugs (Hemiptera: Miridae). J. Econ. Entomol. doi: 10.1093/jee/toy250.

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