Characterization of chlorpyrifos resistance in western tarnished plant bug, Lygus hesperus knight (Hemiptera: Miridae)

Insecticide resistance can be a serious problem in maintaining integrated pest management programs in cropping systems. Unfortunately the complex of Lygus bugs in Western US states has developed increased resistance to multiple insecticide modes of action. To quantify chlorpyrifos resistance within populations of the western tarnished plant bug Lygus hesperus, intensive sampling was conducted and the dose responses to chlorpyrifos was calculated. Chlorpyrifos is an important tool in managing L. hesperus in alfalfa produced for seed and quantifying current resistance levels and the mechanisms associated with resistance among populations of L. hesperus to chlorpyrifos will improve grower’s integrated pest management strategies.  For toxicological bioassay, adults of L. hesperus from multiple populations were tested for resistance to chlorpyrifos (Lorsban 4E) using a Potter Spray Tower. Dose response was calculated on Lygus populations at 5 chlorpyrifos concentrations and mortality was corrected against a nontreated control. Data from the tests were analyzed using Probit analysis to calculate LC₅₀. The LC₅₀ value from each population was compared with the LC₅₀ from susceptible populations to obtain resistance ratio (RR₅₀).  Here we report the results of our preliminary investigations into chlorpyrifos resistance in L. hesperus. Our results are providing reference data to correlate genetic indicators of insecticide resistance to detoxifying mechanisms Lygus bugs to exhibit to overcome exposure to chlorpyrifos..

Keywords: Chlorpyrifos, insecticide, Lygus hesperus, resistance.