Ecdysis Behavior Research Articles

Neural organization of peptide-activated ecdysis behaviors during the metamorphosis ofManduca sexta

Neural organization of peptide-activated ecdysis behaviors during the metamorphosis ofManduca sexta

The role of eclosion hormone in the larval ecdyses of Manduca sexta

Each larval moult in Manduca sexta consists of an identical series of developmental and behavioural events leading up to ecdysis. Injections of eclosion hormone into staged larvae in any instar resulted in the premature elicitation of the larval pre-ecdysis behaviour, comprising a rhythmic sequence of muscle contractions, followed by the larval ecdysis behaviour. A marked depletion of eclosion hormone stores form the ventral chain of ganglia coincided with each larval ecdysis and in the moult to the fifth instar, eclosion hormone activity appeared in the blood at the onset of the pre-ecdysis behaviour. Responsiveness to eclosion hormone for pre-ecdysis and ecdysis behaviour developed about 12 and 6 hr before normal ecdysis, respectively. Elicitation of ecdysis behaviour by exogenous hormone inhibited both subsequent behavioural responses to eclosion hormone and endogenous hormonal release. In conclusion, the behavioural programme involved in each larval ecdysis appears to be controlled by the eclosion hormone.

Physiology of Pupal Ecdysis in the Tobacco Hornworm, Manduca Sexta

ABSTRACT Eclosion hormone activity was found in the brain and ventral ganglia of pharate pupae of Manduca sexta. No activity was detected in the corpora cardiaca-corpora allata complex. At the time of ecdysis the store of activity dropped by 50−75 % in the ventral cord whereas the hormone level in the brain remained unchanged. Also, larvae whose brains were removed at the wandering stage subsequently showed pupal ecdysis behaviour and also had essentially normal levels of hormonal activity in their blood at the start of the behaviour. It was concluded that at pupal ecdysis the hormone responsible for the initiation of the behaviour is released from the ventral nerve cord rather than from the brain. The chemical characteristics of the pharate pupal eclosion hormone were determined. The factors from the brain and ventral nerve cord were both active in a number of adult and pupal eclosion hormone bioassays. Both showed an apparent molecular weight of 8500 daltons and an isoelectric point of about 5−0, values essentially the same as that seen for the adult form of the hormone. We concluded that pupal ecdysis and adult eclosion are triggered by the same hormone but for the former it is released from the ventral nerve cord and, for the latter, from the brain. The choice of release site may depend on whether or not the release is under circadian control.

Electrical activity of neurosecretory axons from the brain of Rhodnius prolixus: Relation of changes in the pattern of activity to endocrine events during the moulting cycle

Ongoing electrical activity was recorded from the axons of neurosecretory cells from the brain of 5th instar Rhodnius prolixus throughout the moulting cycle. Dramatic changes in both the frequency and pattern of electrical activity occur at specific times during the cycle, enabling the timing of release of neurohormones from the brain to be inferred. The level of transport of stainable secretion appears to be closely coupled to the electrical activity at all times. Activity is low in unfed Rhodnius, but within minutes of the insect taking a blood meal, there is a rapid appearance of bursting activity from a number of units, in conjunction with apparently continuous firing components. The bursting activity declines at about 2 h remaining low for the following 5 days, at which time there is a resurgence in the bursting pattern for a few hours. Both peaks of bursting activity immediately precede increases in haemolymph titer of ecdysones, suggesting that release of prothoracotropic hormone occurs on these two occasions. The continuously firing components initiated at feeding maintain a high level for 5 days indicating release of other brain neurosecretions. Intense electrical activity in the form of bursting activity and high apparently continuous pattern resumes shortly before ecdysis and continues until 12 h after. The relationship of neurohormone release at this time to bursicon and ecdysis behavior is discussed.