Role of neurosecretory cells in the photoperiodic induction of pupal diapause of the tobacco hornworm Manduca sexta

Abstract

In the tobacco hornworm, Manduca sexta, pupal diapause can be induced by exposure of fifth-instar larvae to a short-day photoperiod. We studied the effect of surgical ablation of tissues containing the neurosecretory cells of the brain of fifth-instar larvae on the photoperiodic induction of pupal diapause. At the end of the experiments, we immunostained the neurosecretory cells to determine the success of the ablations. Under long-day conditions (LD 16:8 at 22 degrees C), all intact larvae, most of the sham-operated larvae, and control-operated larvae developed into nondiapausing pupae. Under short-day conditions (LD 10:14 at 22 degrees C), most intact, sham-operated, and control-operated larvae developed into diapausing pupae. Removal of type-II cells did not interfere with the photoperiodic response. Under long-day conditions, elimination of type-Ia(1) cells did not affect the incidence of nondiapausing pupae. When type-Ia(1) cells were removed under short-day conditions, however, the incidence of nondiapausing pupae was higher (51%, n = 41) than that of the intact (16%, n = 75), sham-operated (24%, n = 88), control-operated larvae (5%, n = 40), and larvae with type-II cells removed (11%, n = 27). Thus, removal of type-Ia(1) cells can impede induction of diapause. These results indicate that the type-Ia(1) neurosecretory cells have an important role in the induction of pupal diapause.

Roles of PER immunoreactive neurons in circadian rhythms and photoperiodism in the blow fly, Protophormia terraenovae

“…In G. bimaculatus, it has been reported that per knockdown by RNAi suppresses circadian rhythms in locomotor activities and electrical activities of optic lobe neurons (Moriyama et al, 2008). In M. sexta, surgical ablation of per expressing neurons from larval brains caused loss of photoperiodic control of pupal diapause (Wise et al, 2002;Shiga et al, 2003). Although these studies suggest the importance of per or perexpressing neurons in clock mechanisms, there have been no reports on how these neurons integrate or process timing information in the brain.…”

“…Clock-gene-expressing neurons or their protein-immunoreactive neurons have been examined in many species (Frisch et al, 1996;Sauman and Reppert, 1996;Závodská et al, 2005;Codd et al, 2007); however, their roles in behavioural rhythms or photoperiodism have not been identified. Only in the hawk moth Manduca sexta, has the loss of photoperiodic control of pupal diapause been shown after ablation of per-expressing neurons (Wise et al, 2002;Shiga et al, 2003). However, it is not known whether these neurons have roles in circadian rhythm oscillations in this species.…”

Complex steroid–peptide–receptor cascade controls insect ecdysis

“…In moths these corazonin lateral cells also express the circadian clock protein period (PER) involved in the regulation of circadian rhythms (Sauman and Reppert, 1996;Wise et al, 2002). Connection between circadian rhythms and ecdysis is indicated by extirpation manipulations, which showed that these cells may be important for photoperiod-dependent induction of diapause occurring after pupal ecdysis (Shiga et al, 2003).…”

Comparative analysis ofCorazonin‐encoding genes (Crz's) inDrosophilaspecies and functional insights intoCrz‐expressing neurons

“…CRZ or CRZ-containing DLP neurons may have a function related to photoperiodic time measurement. Shiga et al (2003) reported that surgical ablation of CRZ-like immunoreactive neurosecretory cells in M. sexta suppressed pupal diapause under short-day conditions (e.g., 10 hours light, 14 hours dark). From these data, the authors proposed that CRZ-immunoreactive neurons might be a component of the photoperiodic clock that measures lengths of day (or night).…”