Effect of Inactivity Associated with Interstadial Molts on Short-Term Efficacy of Insecticides for Control of Pale Western Cutworm (Lepidoptera: Noctuidae)

Efficacy of sprayed insecticides used for control of pale western cutworm, Agrotis Orlhogonia Morrison, is retarded by 3-5 d if a substantial proportion of the population is molting at the time of application. Cutworms are inactive during a molt and remain 1-3 cm below the soil surface. In natural infestations sampled before treatment, up to 50% of the cutworms were in a premolt or recent postmolt condition and not feeding. In the laboratory at constant temperatures, the molting time associated with the last two larval instars of pale western cutworm accounted for about one-third of the time between cessation of feeding by the antepenultimate instar and termination of feeding by the ultimate instar. Molting time comprises a large component of larval development in cutworms and its effect on behavior, including response to insecticides, has largely been ignored.