Myotropic peptides can be grouped into different families based on their structure. Three Drosophila melanogaster myotropin families are represented by TDVDHVFLRFamide, dromyosuppressin (DMS), pEVRYRQCYFNPISCF, an allatostatin C-type peptide named flatline (FLT), and SDNFMRFamide, a FMRFamide-containing peptide. The structures of DMS, FLT, and SDNFMRFamide differ and each peptide is encoded by a different gene. In addition, the spatial and temporal distributions of DMS, FLT, and SDNFMRFamide are dissimilar. DMS, FLT, and SDNFMRFamide each decreases heart rate; however, their effects are profoundly different. Likewise, the effects of these three myotropins on the frequency of the spontaneous contractions of the crop, an anterior portion of the foregut, differ. DMS stops crop movement without recovery for at least a 10-min period after applying the peptide, FLT significantly decreases the frequency of spontaneous contractions, but its effect partially reverses within a few minutes after applying the peptide, and SDNFMRFamide only slightly decreased crop motility, an effect that was not significantly different from the effect of saline. The differences in the structures, distributions, and activities of DMS, FLT, and SDNFMRFamide suggest their synthesis and release are under different sensory inputs and regulatory mechanisms, and that roles in affecting the frequency of crop contractions differ.