Abstract

The present study evaluated the in vitro bioassay with pupal integumental explants of the mealworm Tenebrio molitor to test the activity of two types of insect growth regulators (IGRs) with ecdysteroidal action. We assessed the imidazole derivative KK-42, that is know as ecdysteroid biosynthesis inhibitor, and the dibenzoylhydrazine RH-0345 (halofenozide) that representing a novel group of IGRs with ecdysteroid agonist action. Two biological endpoint were used, namely the production of ecdysteroid hormone and cuticle secretion in vitro. Also the test was done with and without renewment of the culture medium to test the persistence of action of each compound. Essentially, RH-0345 provoked higher ecdysteroid amounts, while KK-42 a reduction. Interestingly when KK-42 was followed by RH-0345, the inhibitory effect was compensated. In parallel, the deposition of cuticle in vitro was assessed and it was clear that RH-0345 could induce apolysis premature in the integument explants with the formation of a new cuticle. Here the protein and chitin contents of the explants were tested with RH-0345 and three analogous compounds, RH-2485, RH-5992 and RH-5849.

Key words: In vitro bioassay, mealworms, integument, ecdysteroids, cuticle, chitin, proteins.