Studies on the efficacy of selected juvenile hormone analogs and their effects on the metabolism of the eastern spruce budworm Choristoneura fumiferana (Clemens) (Lepidoptera- Tortricidae)

Mulye, Hemendra Shankar (1992) Studies on the efficacy of selected juvenile hormone analogs and their effects on the metabolism of the eastern spruce budworm Choristoneura fumiferana (Clemens) (Lepidoptera- Tortricidae). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The efficacy of seven juvenile hormone analogs (JHAs) in disrupting metamorphosis of the eastern spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), was determined by applying the JHAs topically to early sixth-instar larvae and monitoring the subsequent development. Fenoxycarb was the most effective juvenile hormone analog, with an LD₅₀ of 0.26 μg per insect. Relative lethal effectiveness, based on LD₅₀ values, was fenoxycarb > ZR 9892 > ZR 8487 > S-71639 > methoprene > ZR 9582 > ZR 10151. All of the JHAs, except ZR 10151, caused a wide array of morphogenetic deformities such as formation of larval-pupal intermediates, with precocious evagination of the imaginal wing disks, production of deformed pupae with hemolymph-filled blisters, supernumerary molting, mummified larval-pupal intermediates, and inhibition of molting. -- At a sublethal dose, fenoxycarb and methoprene caused a general disruption in the metabolism of C. fumiferana. As shown by altered levels of carbohydrate, protein, and lipid in the hemolymph and fat bodies. Lipid levels in the hemolymph and fat bodies were severely depleted in fenoxycarb treated insects. -- The predominant class of neutral lipid in the hemolymph was diacylglycerol, and in the fat body triacylglycerol. The fatty acid complement of the hemolymph and fat body lipids was represented by several saturated and unsaturated fatty acids. These qualitative profiles were unaffected by fenoxycarb treatment. -- The capacity of fat bodies from fenoxycarb treated larvae to synthesize lipids in vitro was impaired. The effect of fenoxycarb treatment on lipid synthesis appears to be at least partially direct, since addition of fenoxycarb to the incubation medium of fat bodies from untreated larvae resulted in reduced lipid synthesis. It was found that impairment occurred both in the pathway leading to fatty acid synthesis, and the subsequent pathway leading to complex lipid synthesis, as shown by reduced incorporation of radiolabelled precursors into lipid, as well as diminished capacity of the fat body nytosolic enzymes to synthesize fatty acids in vitro. -- Fenoxycarb treatment also altered the types of complex lipids synthesized from labelled acetate, but not in the types of complex lipids synthesized from labelled palmitate, suggesting that the JHA affected the initial step of lipid synthesis, i.e. fatty acid biosynthesis. The ability of fat bodies from fenoxycarb treated budworms to oxidize preformed fatty acids jln vitro, via the β-oxidation pathway, was significantly impaired in the early (24 hours post treatment) sixth instar C. fumiferana larvae. -- These studies demonstrate that lipid metabolism was severely perturbed in C. fumiferana as a result of fenoxycarb treatment.

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