Evidence of a stimulatory effect of cyclic AMP on corpus allatum activity in Manduca sexta

Injection of dibutyryl-cAMP prevents cuticular melanization of black Manduca sexta larvae, whose pigmentation is related to a defect in the control of the corpus allatum. The cAMP analog has no effect in allatectomized black larvae. Significant stimulation of corpus allatum activity was obtained in vitro with compounds which elicit or mimic elevated intracellular cAMP levels (dibutyryl-, 8-bromo-, N6 benzoyl-, and 8-thiomethyl-cAMP, 3-isobutyl-1-methylxanthine), but not with dibutyryl-cGMP. Relatively inactive glands, such as those on day 4 of last larval stadium or from black mutant larvae, were more sensitive to these compounds than glands actively synthesizing JH/JH acid. JH acid synthesis by corpora allata taken after pupal commitment in the last larval stadium (days 6 and 8) was not stimulated by either dibutyryl-cAMP or 3-isobutyl-1-methylxanthine, but day 8 glands appeared to be inhibited by dibutyryl--cAMP. The results indicate that a cAMP second messenger system is involved in the transduction of signals which stimulate JH/JH acid synthesis by Manduca corpora allata prior to pupal commitment and suggest that it may be involved in the inhibition of JH acid synthesis after commitment. They also imply that the proposed hemolymph factor to which the black mutant corpora allata are differentially sensitive interfaces with the cAMP system.