The effect of ingested benzoylphenylurea on the ultrastructure of the cuticle deposited during the last larval instar of Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae)

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Abstract
The sequential ultrastructural changes induced by the ingestion of a sublethal dose of a benzoylphenylurea, chlorfluazuron, were investigated in sixth-instar larvae of the spruce budworm, Choristoneura fumiferana. The 4-day-old, postecdysis larvae showed the most profound ultrastructural effects. The newly formed endocuticle showed an absence of lamellae, indicating the lack of formation of chitin microfibrils. Vacuolated and fibrous areas containing an amorphous material, possibly proteinaceous, were observed in the region where lamellae would normally be present. The epidermal cells had microvilli with swollen and rounded tips. These cells also contained oval vesicles containing granular amorphous material. The in vivo inhibition of chitin deposition by this benzoylphenylurea was readily apparent. It is suggested that the amorphous material observed in the zone where chitin was lacking is the protein component of the glycoprotein chitin. It is possible that the benzoylphenylurea inhibits the assembly of the amino sugar with the protein to form microfibrils.

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