The termination of diapause in Trogoderma granarium Everts (Coleoptera, Dermestidae)

When subjected to an increase in temperature from 30 to 37°C, both the density-dependent diapause (DDD) and the density-independent diapause (DID) of Trogoderma granarium were terminated in about 10 days. However, under severe crowding, a few DDD larvae took as much as 100 days to pupate at 37°C.

At 30°C, most larvae that had entered diapause in isolated cultures pupated spontaneously during a brief period sometime after they were 3 months old; for most populations of larvae studied such pupation occurred at about 5 months of age. Renewal of food had little influence on the termination of DID. A corresponding burst of pupation, although of only one quarter of individuals, was also recorded for DDD larvae kept crowded in old flour. The most effective termination of DDD, at 30°C, was achieved by isolating the larvae and providing new food together. This treatment brought about a small immediate burst of pupation and also enhanced the subsequent spontaneous pupation so that altogether about 86 per cent of the larvae pupated.

The adaptive value of these reactions in the warehouse environment is discussed. It is suggested that the significance of some of the features of the diapause of T. granarium may be explicable only in relation to its primitive habitat, possibly the nests of insects, in which the diapause must have originated.