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Baseline Susceptibility, Resistance Detection and Selection for Resistance in Aphis glycines (Hemiptera: Aphididae) to the Neonicotinoid Insecticide, Thiamethoxam
The risks associated with soybean aphid (SBA), Aphis glycines Matsumura and other early pest infestations in the North Central soybean systems stimulated the use of seeds treated with neonicotinoid insecticides, especially thiamethoxam. SBAs haven’t yet developed resistance to this insecticide, however, there is a concern that this increased selection pressure may lead to resistance. In vivo bioassays were conducted to determine the susceptibility of SBA to thiamethoxam among North Central U.S. populations. Concentration-mortality data were collected using glass-vial and detached-leaf bioassays. Our results indicate that both bioassays reliably detected shifts in tolerance between different SBA clones, and the magnitude of these differences was low. Age-synchronized monitoring is known to provide more consistent results; however, it is more laborious than mixed-age monitoring. An experiment was conducted to evaluate the presence of age-specific susceptibility in SBAs using detached-leaf bioassays. Our results indicated that bioassays performed with mixed ages of aphids is reliable and more practical than age-synchronized monitoring. In addition, it was possible to incorporate growth rates measurements, which improves the assessment of population- level responses. A multigenerational selection to thiamethoxam was performed using a newly developed whole-plant systemic bioassay. After approximately 7 days of exposure, surviving aphids were recovered and used to calculate the lethal concentrations using glass-vial bioassays. Our results provided evidences of a non-stable resistance evolution to thiamethoxam, which indicates the presence of fitness-cost. A greenhouse experiment was conducted to determine the life history parameters of a thiamethoxam pre-selected, and non-selected SBA populations in whole-plant systemic bioassays. Significant differences associated with life history parameters resulted in the rates of population growth for both colonies. Decreased survivorship and population growth inhibition occurred at singular concentrations for each colony. Bio- demography measurements were shown to be important and complementary to bioassays in determining and predicting the sub-lethal effects of thiamethoxam on soybean aphids at population level. The results presented in this dissertation provide important information regarding SBA susceptibility to thiamethoxam at individual and population levels, as well as to better understand the risks and rates of resistance evolution within this species.
Ribeiro, Matheus Geraldo Pires de Mello, "Baseline Susceptibility, Resistance Detection and Selection for Resistance in Aphis glycines (Hemiptera: Aphididae) to the Neonicotinoid Insecticide, Thiamethoxam" (2017). ETD collection for University of Nebraska - Lincoln. AAI10271836.