Insecticide Efficacy and Resistance Mechanisms of Tarnished Plant Bug Populations in Southeastern Cotton

Economically damaging populations of the tarnished plant bug (Lygus lineolaris) have been documented since 2013 in Virginia and North Carolina. In response, cotton acres sprayed with broad-spectrum insecticides has increased dramatically in these states. Given the sudden rise of L. lineolaris and lack of published research on this pest in the Southeast, a regionally specific insecticide resistance management (IRM) strategy is needed to help growers minimize yield loss and delay insecticide resistance. This study seeks to 1) quantify insecticide resistance currently present in L. lineolaris populations throughout Southeastern cotton-producing states (VA, NC, SC, AL, and GA), and 2) determine potential mechanisms of insecticide resistance. To achieve these objectives, L. lineolaris collections across the Southeast were made in primary weedy hosts and cultivated hosts. Each of these populations was used for glass-vial bioassays to determine efficacy and level of resistance to various insecticides, including bifenthrin and acephate (broad-spectrum chemistries), and sulfoxaflor and thiamethoxam (narrow spectrum chemistries). The LC₅₀ values or lethal concentration to kill half the population were recorded using probit analysis, and all tests were compared to a susceptible lab strain LC₅₀ to calculate resistance levels or resistance ratios (i.e., RR₅₀). Biochemical assays were also performed to quantify cytochrome P450-dependent O-demethylation (CYT), general esterase (EST), and glutathione S-transferase (GST) activity in resistant populations. Findings from this study will be used to develop a comprehensive IRM package that will equip Southeastern cotton growers with the knowledge to increase yield potential, and minimize the economic and environmental impacts of over spraying insecticides.