Comparison of Insecticide Susceptibility between Fall Webworm, Hyphantria cunea (Lepidoptera: Arctiidae) and Its Parasitoid Fly, Exorista japonica (Diptera: Tachinidae)

The insecticide susceptibility of the Fall Webworm, Hyphantria cunea and its parasitoid fly, Exorista japonica, was studied. Larvae of H. cunea were hardly susceptible to organophosphorus insecticides, such as fenitrothion (LD₅₀=> 100 μg/larva) and isoxathion (LD₅₀=54 μg/larva). However, adults of H. cunea were quite susceptible to fenitrothion (LD₅₀=1.4 μg/male and 2.2 μg/female). Adults of E. japonica emerging from pupa of H. cunea were very susceptible to fenitrothion (LD₅₀ =0.082 μg/adult). The results suggest that a judicious choice of insecticide is necessary to control H. cunea, if E. japonica is used as a biological control agent, too.