Development of Diagnostic Monitoring Techniques for Larval Pyrethroid Resistance in Heliothis spp. (Lepid Resistance Monitoring in H. virescensoptera: Noctuidae) in Cotton

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Abstract
Techniques were developed to monitor pyrethroid resistance in larval stages of the tobacco budworm, Heliothis virescens (F.), and the bollworm, H. zea (Boddie). Neonate larvae as well as the other instars of a susceptible tobacco budworm strain were tested with cypermethrin with a glass vial technique to estimate concentration-mortality lines. An approximate LC80-90was selected to discriminate for resistance in each larval stage. Tests with pyrethroid-resistant tobacco budworms at these concentrations showed minimal mortality. Tests with bollworm larvae resulted in 93-100% mortality for the different stages. A formula [100 – (MF/MS ×100)] allowed us to determine the percentage of insects resistant in the field and simultaneously to correct for partial survival of susceptible insects at the discriminating concentration used. The methods were then tested on field-collected insects at times when numbers of eggs, larvae, or both, justified concern. Accuracy of the method was confirmed with another technique for measuring insecticide resistance. These techniques were developed to supplement monitoring data for adult resistance, to provide timely and accurate resistance data for the stage when the insect is an actual pest, and to provide producers or consultants with a predictive bioassay useful in detecting resistance before an insecticide application.