Mohammad-Amir Aghaee, Ph.D.
Resistance Monitoring for Cotton Bollworm
P.I : Mohammad-Amir Aghaee and Dominic Reisig
Problem: Most resistance monitoring for Helicoverpa zea in Bt cotton occurs by collecting insects randomly and placing them on diet overlaid with purified Bt protein. This method underestimates the threat of resistance, especially when we observe that certain traits do not perform as well as they are supposed to in the field. So how can we bridge this gap between field and laboratory observations?
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The answer may lie in a field based approach similar to one developed for corn rootworm in corn. Field realistic doses from live tissues expressing Bt protein are the key. But the question remains, which tissue on the cotton plant should be selected for this task?
Methods: To answer this question we focused on structures on the three reproductive stages of the fruiting body: squares, flowers, and bolls. The structures were bracts, sepals, walls, petals, and any holes into the ovary. We tagged 40 bolls, 40 squares, and 40 flowers per plot and quantified area of damage (square mm) to said structures and recorded tissue abscission over the course of five weeks, and also measured levels of Bt expression in plant tissues.
We measured these on four different varieties (non-Bt, WideStrike, Bollgard II, and TwinLink) across three years (2014-2016). The varieties represent different combinations of different Cry proteins (insecticidal toxin)
Logistic regression and path analysis was used to determine the injured structures that likely contributed to abscission. The goal was to select a specific tissue, where injury would not lead to abscission and therefore could be useful for in situ resistance monitoring.
Preliminary Results and Conclusions: In all reproductive tissue types, holes into the ovary were positive indicators of abscission, while sepal and bract feeding was not. We found varietal differences in bract feeding patterns on bolls and flowers. The differences found in bract feeding can potentially be used for in situ resistance monitoring, but should be validated using resistant and susceptible H. zea. The Bt expression data is still being gathered.
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Funding: This project has been made possible with the support of USDA-NIFA
Plant Bug Thresholds and Management
P.I : Mohammad-Amir Aghaee and Dominic Reisig
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Problem: Tarnished plant bug (Lygus lineolaris, TPB) has become a great problem in cotton because of yield losses and the associated costs of treatment. This problem began as an unintended consequence of adopting Bt cotton, which reduced the amount of insecticide sprays for the control of cotton bollworm and budworm. Previously, frequent broad-spectrum insecticide applications for bollworm had also controlled several secondary pests such as the L. lineolaris (Musser et al. 2009). Since 2009, the percentage of total cotton acres sprayed for TPB in North Carolina has climbed close to 50%, (Williams 2015).
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Methods: We conducted an experiment to reevaluate the use of currently recommended treatment thresholds of 8 and 16 L. lineolaris adults per 100 sweeps for a low and high threshold respectively. We also examined the most effective time to spray L. lineolaris, testing sprays of Transform® at pre-bloom, early bloom, late bloom, pre-boll, with an untreated control.
Preliminary Results: We found that L. lineolaris adult populations did not differ between treatments, although the fluctuations coincided with the start of bloom as was expected. L. lineolaris nymphal populations were high in the late bloom and control plots but showed no difference the threshold and early treated plots. There were no differences in square retention after the second week of observations. Yield data (pounds of lint per acre) revealed informative differences in treatment where the low and high threshold plots and the pre-bloom plots had the highest yields compared to the rest of the plots. Preliminary conclusions are that current thresholds are appropriate and early spraying during the first weeks of squaring is highly recommended. However, the use of a non-pubescent variety and an insecticide that is no longer recommended for L. lineolaris use represents a worst-case scenario that encourages high populations of L. lineolaris. Further work is needed with variety selection and recommended insecticides for managing L. lineolaris in North Carolina.
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Funding: This project has been made possible by Cotton Inc. and is being conducted in collaboration with Prof. Sally Taylor at Virginia Tech.
Brown Marmorated Stink Bug in the Coastal Plains
P.I : Jim Walgenbach Eastern NC collaborators: Mohammad-Amir Aghaee and Dominic Reisig
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Problem: Brown marmorated stink bug (Halyomorpha halys) has been in the state of North Carolina since 2009. Since then it has spread through the counties west of I-95, and has been conspicuously absent from the coastal plains regions in NC and further south. The question is why is this occurring, one reason may have to do with host abundance and the other with phenology.
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Methods: In 17 counties across the state we placed pyramid traps with Mergantol and MDT synergist to attract BMSB adults and nymphs. These traps were located on the edge of soybean fields across from a wooded area. All trees and shrubs within 50 meters of the traps and 20 feet into the woods were identified to genus and counted. BMSB were collected with the help of county extension agents from June through October, at least twice a month.
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The phenological study is being undertaken by Chris Bergh and Jim Walgenbach. I am contributing to that study by collecting data on BMSB that are emerging from overwintering boxes from January through June.
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Results: Please Contact Chris Bergh or Jim Walgenbach for overwintering study results.
email: Jim_Walgenbach@ncsu.edu or cbergh@vt.edu
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Funding: This project falls under a Specialty Crops Regional Initiative grant (USDA) led by Dr. Jim Walgenbach of NC State University.