Effect of RH-2485 on development, metamorphosis and synthesis of major proteins in female silkworm Bombyx mori

Abstract

Toxicological data on silkworm Bombyx mori are quite comparable to those of other lepidopteran pest insects, therefore, it is considered as a suitable model for exploring effects of any new synthetic formulations. In this study, female V instar larvae of silk moth B. mori were chosen to evaluate the lethal and sublethal toxicity effects of RH-2485 (methoxyfenozide), a non-steroidal ecdysteroid agonist and to substantiate the ecdysteroid mimicking action of RH-2485 on ovary development, vitellogenin incorporation and egg production in isolated pupal abdomen (IPA). Probit analysis was carried out to find the median lethal dose (LD50) from 96 h cumulative mortality percent. Protein profile of haemolymph, fat body, ovary and eggs were separated in SDS-PAGE. Western blot analysis was carried out to confirm vitellogenin in the ovary. Sublethal effects on feeding, cocoon spinning, pupation, adult emergence and egg production were studied at doses of 1/5th, 1/10th and 1/20th of LD50. Significant changes were observed in all these parameters at all three sublethal doses. The morphological effects were related to underlying biochemical changes by finding the changes in haemolymph, fat body, ovary and egg protein profile. Marked changes were observed in storage proteins (80 kDa) and 30 kDa proteins in the haemolymph at all three sublethal doses. The larvae that escaped the sublethal effects at a dose of 1/20 of LD50 and emerged as adults with malformed wings produced significantly lower number of eggs. The isolated pupal abdomen (IPA) treated with RH-2485 did not metamorphose into adult but the oocyte development and vitellogenesis were normal but the egg precursor processing was incomplete leading to failure in choriogenesis.