Terminal steps in JH biosynthesis in the honey bee (Apis mellifera L.): developmental changes in sensitivity to JH precursor and allatotropin

Juvenile hormone (JH) is considered the prime endogenous signal for the ind uction of queen development in honey bees (Apis mellifera L.). At the begin ning of the last (5th) larval stadium, worker corpora allata synthesize les s JH than queen corpora allata as a consequence of a limited production of JH precursors and a caste- and stage-specific block of the terminal step in JH biosynthesis, As previously shown, the Manduca sexta allatotropin stimu lates JH biosynthesis in honey bee corpora allata in a dose-dependent and r eversible manner, but can not overcome the stage-specific block in the term inal step of JH biosynthesis that is typical for worker early 5th instars. In experiments with M. sexta allatotropin and with the JH precursor farneso ic acid, we found characteristic stage-specific differences in their effect s on JH biosynthesis. From the end of the spinning stage on, corpora allata could be stimulated by farnesoic acid to a much higher extent than in earl ier developmental stages, suggesting a sudden increase in epoxidase activit y. Manduca sexta allatotropin, however, stimulated corpora allata activity until the end of the spinning stage, at which time the corpora allata becom e suddenly insensitive. These data suggest that in worker larvae, important changes in the regulation of the terminal enzymatic steps in JH biosynthes is occur at the transition from the spinning stage to the prepupal stage. H owever, the analysis of in vitro activities of the involved enzymes, O-meth yltransferase and methyl farnesoate epoxidase, remained inconclusive. (C) 2 000 Elsevier Science Ltd. All rights reserved.