Effects of Diploptera punctata allatostatins on juvenile hormone biosynthesis and endogenous juvenile hormone III levels in virgin and mated female Periplaneta americana

Abstract

Corpora allata from 4-day-old virgin and sexually mature female Periplaneta americana were tested for sensitivity to inhibition of juvenile hormone biosynthesis in vitro by four allatostatins from Diploptera punctata. Two of these allatostatins were also tested for their ability to lower juvenile hormone levels in vivo when injected in aqueous solution. In 4-day-old virgin females (showing comparatively low rates of juvenile hormone synthesis) corpora allata were sensitive to all four neuropeptides. Inhibition of juvenile hormone synthesis was roughly equivalent at the single dose tested (58–74% inhibition @ 10 −5 M). By contrast, corpora allata from mid-cycle sexually mature females (in which juvenile hormone synthesis approaches maximum rates) were sensitive only to D. punctata allatostatin 4. Investigation of the sensitivity of corpora allata to allatostatins 1 and 4 throughout the reproductive cycle revealed that at no stage did allatostatin 1 cause more than 25% inhibition of juvenile hormone synthesis. Allatostatin 4 however, caused a moderate inhibitory response early in the cycle (33–71%), rising to a highly significant response (81–97%) towards the end of maximal oocyte growth when endogenous (control) rates of juvenile hormone synthesis are naturally declining. The activities of the Diploptera allatostatins against Periplaneta corpora allata in vitro are matched by their actions in vivo. Injections of allatostatins 1 and 4 (100 μg/insect) into day-4 virgin P. americana were effective in bringing about a lowering of total body JH III levels 12 h post-injection. Similar injections of allatostatin 1 into mid-cycle mated females produced no apparent effect but injection of allatostatin 4 did result in a substantial reduction (50–70%) of endogenous total body JH III levels in these insects.