Regulation of development of the grain beetle Tenebrio molitor by neuropeptides

Abstract

Summary Two neuropeptides (NPs), hydra head activator (HHA), and the luteinizing hormone releasing hormone (LHRH), were used to study their effects on the development of the larvae of the grain beetle Tenebrio molitor (mealworms). The larvae received the NPs in the course of development at the beginning or at the end of instar. The LHRH given at the beginning of the instar stimulated molting and pupation in larvae; it did not affect molting in the late period of the instar. The C-end fragment of LHRH(9–10) produced fewer molts and increased the duration of the instar period. The effect of this fragment was weak when it was injected at the initial period of the instar; it was considerably stronger in the end of the instar. It inhibited development when administered during the last instar. On the contrary, the N-end fragment of the LHRH(1–2) stimulated growth and development of larvae. The action of these NPs can be connected to the function of the hormones of metamorphosis. The HHA administrated to the larvae at different days of the instar stimulated molting but in the last instar it delayed pupation. The C-end of the HHA(7–11) stimulated molting when injected during the whole period of the instar. The other C-end fragments, the HHA(8–11) and HHA(9–11) had inhibitory effects on the molting. The injection of the N-end fragment of the HHA(1–5) had no effect. The action of HHA and its fragments did not correlate with the function of the hormones of metamorphosis.