In vitro and in vivo effects of myo-active peptides on larvae of the tomato moth Lacanobia oleracea and the cotton leaf worm Spodoptera littoralis (Lepidoptera; Noctuidae)

Neuropeptides from five different neuropeptide families [Manduca sexta allatostatin (Manse-AS), and Manse-AS deletion analogue(5-15), M. sexta allatotropin (Manse-AT), leucomyosuppressin, perisulfakinin, and myoinhibitory peptide I (MIP I)] were assayed for their ability to affect the development and food consumption of penultimate and last larval instars of two lepidopteran species, L. oleracea and S. littoralis. Injections of Manse-AS deletion analogue(5-15), Manse-AT, perisulfakinin, and MIP I had no observable effects on development, food consumption, or mortality compared to controls. Single injections of Manse-AS significantly reduced the weight gain and increased mortality of L. oleracea and S. littoralis larvae compared to controls. By contrast, feeding Manse-AS to L. oleracea had no such effects. These differences were probably due to the degradation of the peptide by digestive enzymes in the foregut of L. oleracea. In studies in vitro, perisulfakinin, and MIP I had no effect on the spontaneous foregut contractions of L. oleracea larvae. Leucomyosuppressin, however, had myoinhibitory effects on the foregut. Single injections of leucomyosuppressin significantly reduced the weight gain and food consumption of L. oleracea and S. littoralis larvae and increased mortality. These data suggest that the deleterious effects observed in vivo were due to the myoinhibition by Manse-AS and leucomyosuppressin of the normal peristaltic movements of the gut either by the intact peptide or by its cleavage products resulting from degradation in the haemolymph.