Studies on the Dermestid beetle Trogoderma granarium Everts—IV. Feeding, growth, and respiration with particular reference to diapause larvae

Abstract

Feeding, growth, respiration, and behaviour have been studied in the diapause and non-diapause larvae and in the post-larval stages of the Khapra beetle. In any one instar of a non-diapause larva, both feeding and respiration increase towards the middle of the instar and fall again towards the end. The relationship of the respiration curve to the type of food is discussed. It is apparent that the larva uses more oxygen when feeding and assimilating food than it does when re-organizing at ecdysis and metamorphosis. The diapause larva stays in a refuge for long periods in a dormant condition without feeding, with its rate of respiration reduced much below that of other post-oval stages. If the dormant larva is disturbed daily or denied access to a refuge, this rate is increased only slightly, even though the larva is capable of walking about. The dormant larva moults occasionally, although its rate of respiration increases little at the time of moulting. The function of the extra moults may be partly to facilitate changes in the size and behaviour of larvae. The diapause larva feeds for short periods between long periods of dormancy. Feeding is accompanied by a large increase in the rate of respiration, just as it is with a non-diapause larva. It appears that this feeding during diapause greatly extends the time a larva can live in diapause. When an experimental treatment is altered, with the result that the rate of respiration is changed, the change in rate is often delayed until after the larva has moulted. The extension of larval life by dormancy and slow respiration, with occasional short periods of rapid respiration associated with feeding, is regarded as a true facultative diapause. The endocrine control of the diapause and of the moulting during diapause is discussed.