A juvenoid. R394 (Ethyl 9-cyclohexyl-3,7-dimethyl-2,4-nonadienoate) was applied topically to 5th instar silkworm, Bombyx mori L. larvae (Hybrid: KA x NB4D2) at a dose of 0.039 nl/larva at 24, 48, 72 and 96 h, for silk yield improvement. Three major selected tissues viz., posterior silk gland (PSG), haemolymph and fat body were collected from fully-grown larvae and the total protein, total carbohydrate and total lipid contents were estimated following standard procedures. The result indicated that the content of these primary metabolites varied significantly in the selected tissues depending on the time of juvenoid application. The highest protein content was observed in the haemolymph and silk gland in the larvae treated at 72 h whereas the fat body protein content was lowest for the same treatment. The total carbohydrate was recorded lowest in the 72 h treated larvae as against the highest in the control both in haemolymph and fat body with no significant change in PSG. The total lipid content did not show any notable variation in the concentration on juvenoid administration except in the silk gland treated up to 72 h which showed a decline. The results indicate that the juvenoid induces tissue-specific responses in terms of turnover in primary metabolites which commensurates with the corresponding changes observed in the cocoon weight and cocoon shell weight.
Eicosanoids mediate induction of immune genes in the fat body of the silkworm, Bombyx mori