Technical Abstract: Juvenile hormone (JH) is considered the prime endogenous signal for the induction of queen development in honey bees (Apis mellifera L.). At the beginning of the last larval instar, worker corpora allata synthesize considerably less JH than queen corpora allata due to 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 stimulates JH biosynthesis in honey bee corpora allata in a dose-dependent and reversible manner, but can not overcome the stage- specific block in the terminal step of JH precursor farnesoic acid, we found characteristic stage-specific differences regarding their effects 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 earlier development stages, suggesting a sudden increase in epoxidase activity. M. sexta allatotropin, however, stimulated corpora allata become suddenly insensitive. These data suggest that in worker larvae, important changes regarding the regulation of the terminal enzymatic steps in JH biosynthesis occur at the transition from the spinning stage to the prepupal stage.