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The involvement of second messengers in modulating Schistocerca gregaria rectal ion and fluid transport was investigated using two in vitro bioassay systems: everted rectal sacs and rectal flat sheets. Various agents known to block or activate specific signal transduction pathways were employed in these bioassays. Cyclic AMP stimulated rectal fluid reabsorption (J(v)) and Cl- transport (I-sc) to the same extent as aqueous extracts of corpus cardiacum storage lobes. Cyclic GMP also partially (50%) stimulated both rectal J(v) and I-sc. Exogenous Ca2+ was not required for the maintenance of rectal transport, indeed Ca2+ free conditions increased the amount of stimulatable J(v). There was some evidence indicating intracellular Ca2+ may play a minor role in controlling rectal transport. The phospholipase C mediated signal transduction pathway was not involved with the stimulation of rectal transport, and appeared to have an inhibitory role. Neuroparsins, antidiuretic neuropeptides from Locusta migratoria, showed no activity upon either S. gregaria rectal ion or fluid transport. The findings of this study show that the two closely related insects possess discrete antidiuretic factors which stimulate rectal transport via different signal transduction pathways. (C) 1996 Wiley-Liss, Inc.