Management of Aphis gossypii Populations and the Spread of Cotton leafroll dwarf virus in Southeastern Cotton Production Systems

Abstract

Cotton aphid, Aphis gossypii Glover is a highly polyphagous pest known to cause both direct and indirect damage to cotton. Management of A. gossypii is a concern in Alabama due to two emerging problems, insecticide resistance, and transmission of Cotton leafroll dwarf virus (CLRDV). The overall objective of this research was to evaluate management tools of A. gossypii in cotton. The objective of Chapter 2 was to quantify the susceptibility of A. gossypii populations collected from different cotton production regions across Alabama by calculating LC50s from dose-response curves to quantify susceptibility to imidacloprid. On average, field collected populations were 69.71 and 81.16 times more resistant than the susceptible colony at 48 and 72 h respectively. These results indicate variable levels of susceptibility among cotton aphid populations with some exhibiting high levels of resistance. Insecticide applications targeting A. gossypii should be minimized to reduce selection for insecticide resistance. The Chapter 3 objectives were to investigate the efficacy of cultural and aphid management strategies on reducing final CLRDV incidence and monitored aphid population dynamics in relation to timing of CLRDV spread. In this study, chemical and cultural practices evaluated did not reduce final incidence of CLRDV. Final CLRDV incidence was nearly 100% in all plants sampled in GA, and incidence ranged from 60 – 100% across plots in AL. Although insecticide use did reduce aphid populations in the field, it did not reduce the proportion of plants infested with aphids. Aphid monitoring showed that Aphis gossypii and Protaphis middletonii Thomas were the dominant species collected from pan traps. Results from the sentinel plants objectives to monitor spread of CLRDV into the field identified three distinct time periods of spread concurrent with aphid trapping efforts, and two of them coincide with aphid dispersal events. Further research is needed to understand the relationship between aphid population dynamics and CLRDV spread, in addition to investigation of other management strategies to reduce CLRDV in cotton.