Development of Malformed Larvae Induced by a Benzoylphenyl Urea Insecticide, Chlorfluazuron, in the Common Cutworm Spodoptera litura Fabricius

Abstract

Chlorfluazuron, a new benzoylphenyl urea insecticide developed by Ishihara Sangyo Kaisha Ltd., was very effective on Spodoptera litura larvae. At lethal dosages, larvae turned translucent and then black, or split the old cuticle but failed to exuviate. At lower dosages, most of the larvae had pale regions with dark stripes and stains. The integument of a larva enclosed in the translucent old skin was torn at regions close to the sutures between the segments, which seemed arthrodial membranes, and at the last and thoracic dorsal segments. These rips appeared at positions corresponding to stripes and stains in a successfully molted larva. Based on these observations, various malformations of the cuticles were judged to be results from the disruption in forming pre-ecdysal new cuticles. The regions close to the sutures and the last and thoracic dorsal segments were more susceptible to the compound than other regions. Larvae that neither fed nor grew after successful molt were also observed, probably because the mouthparts were disrupted by the compound.