Datana ministra larvae possess a gland situated in the ventral anterior portion of the prothorax. The gland consists of a single sac and is only charged with secretion in the last instar. Its orifice, a simple slit, opens into a transverse invagination of the integument in the cervical margin of the prosternite. The components of the gland have been identified by GC and GCMS and have been shown to be dodecanol, dodecyl acetate, and dodecyl formate. The morphology of the gland and the chemistry of the secretion are discussed in relation to other notodontid larvae which have been investigated. It is conjectured that the secretion is not defensive in nature but may function as a dispersal pheromone.
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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