Further Studies on Lipid Metabolism in the Insect Parasite, Exeristes roborator (Fabricius)

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Abstract
The fatty acid pattern of the parasite Exeristes roborator reared on chemically defined fatty acid free diets was composed almost entirely of palmitate, 25%; palmitoleate, 15%; stearate, 10%; and oleate, 50%. Dietary 2-14C-acetate was readily incorporated into these fatty acids and their relative specific acivities determined. Triglyceride supplements resulted in increased levels in the parasite of the corresponding fatty acids, but these increases were accompanied by decreased specific activities suggesting deposition of dietary fat rather than increased de novo metabolic activity. In contrast, altered dietary lipid composition in host reared parasites resulted in much more striking changes in the fatty acid composition and the specific activities of the individual fatty acids remained the same demonstrating altered de novo metabolic activity. Marked alterations in the basal fatty acid composition were brought about by dietary phenylmethyl sulphonyl fluoride, demonstrated to be an inhibitor of fatty acid synthesis. This action was accompanied by decreased survival and increased development time. Parasites readily incorporated radioactivity from radioactive precursors into their various lipids. Parasites reared on artificial diets supplemented with 2-14C-acetate incorporated the largest proportion of radioactivity into the phospholipid and hydrocarbon, sterol ester and wax fractions, whereas host reared parasites incorporated the largest proportion into the phospholipid and triglyceride fractions. The results suggest that triglyceride synthesis and deposition is minimal in parasites reared under the artificial nutritional regime tested as these parasites contained half the lipid of those reared on host insects. Phenylmethyl sulphonyl fluoride had no effect on the relative distribution of radioactivity in the various lipid classes. Exogenous lipid supplied as long chain acyl-CoA derivatives inhibited isolated fatty acid synthetase activity similarly in E. roborator and its host Galleria mellonella. Their action as effectors on this portion of the de novo synthesis system, therefore, fails to explain the increased metabolic activity observed in host reared parasites following alteration in dietary lipid composition.

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