The type-A allatostatins A (AST-A) are a group of insect peptides with a common C-terminal motif Y/FXFGL-NH2. The existence of at least four putative type A Drosophila melanogaster ASTs (called type A drostatins or DST-As) has been predicted from the sequence of a recently cloned DST-A preprohormone [C. Lenz et al. (2000) Biochem. Biophys. Res. Commun. 273, 126-1131]. SRPYSFGL-NH2, (DST-3A), the only DST isolated from Drosophila so far, activated the first cloned DST-A GPCR (DAR-1) [N. Birgul et al. (1999) EMBO J. 18, 5892-5900]. A newly cloned orphan Dm GPCR, which shares 47% overall and 60% transmembrane region sequence identity with DAR-1, was classified as a second putative Dm DST-A receptor (DAR-2) [C. Lenz et al. (2000) Biochem. Biophys. Res. Commun. 273, 571-577]. Although activation of DAR-2 by DSTs has been postulated, no experimental evidence for that has been presented to date. In this study, we expressed both DAR-1 and DAR-2 in CHO cells and used a GTP gammaS and a Ca2+ mobilization assay for pharmacological evaluation of the receptors. Synthetically prepared DST-As, as well as selected Diplotera punctata (cockroach) ASTs, activated DAR-I and DAR-2 in both functional assays indicating ligand redundancy and cross species activity. Cell pretreatment with pertussis toxin led to some differences in the nature and magnitude of signaling pathways at the DAR-I and DAR-2 receptors, suggesting possible differential coupling to cellular effector system(s) and distinct biological functions of each receptor in vivo.