Ion transport peptide and ion transport peptide-like regulate ecdysis behavior and water transport during ecdysis in Gryllus bimaculatus

Ion transport peptide (ITP) and ITP-like (ITPLs) are pleiotropic bioactive peptides in insects. Although the contribution of these peptides to ecdysis has been studied, the precise regulatory mechanisms remain poorly understood. Here, we characterized the functions of itp and itpl variants in the two-spotted cricket, Gryllus bimaculatus. Reverse transcription-quantitative PCR and whole-mount in situ hybridization revealed that itp was expressed in the brain and terminal abdominal ganglion, whereas itpl variants were expressed in all ganglia of the central nervous system. Simultaneous knockdown of itp and itpls disrupted ecdysis behavior and water transport from the gut into the hemolymph during molting. Nevertheless, knockdown of itpls without influencing itp expression did not significantly affect ecdysis behavior but caused a reduction in hemolymph mass. Although water transport into the hemolymph is considered necessary for the swelling required to split the old cuticle layers during molting, a rescue experiment by injection of water or cricket Ringer's solution into the hemolymph of knockdown crickets did not recover the normal phenotype. Therefore, we propose that ITP/ITPL control ecdysis behavior probably not by regulating water transport from the gut into the hemolymph in crickets.