UNDER-SIZED LARVAE FROM SHORT-DAY ADULTS OF THE BLOW FLY, CALLIPHORA-VICINA, SIDE-STEP THE DIAPAUSE PROGRAM

Larvae of Calliphora vicina R.-D. (Diptera: Calliphoridae) hatching fr om eggs laid by adult females exposed to short day length, and then ra ised in darkness at 11 degrees C, normally enter diapause rather than undergoing prompt pupariation. However, if the feeding stage is curtai led by premature extraction of larvae from their food, or if the larva e are subjected to severe overcrowding, smaller larvae side-step the d iapause programme to become miniature puparia, whereas larger larvae p roceed to diapause as fully-fed ones. In addition, smaller diapausing larvae show a shorter (or less intense) diapause than full-sized larva e. Apart from the smallest individuals, flies can emerge from these mi niature puparia and in some cases are capable of laying eggs; this sug gests that avoidance of diapause may allow undersized individuals an o pportunity to reproduce before winter sets in. Fat determinations perf ormed on larvae and pupae of various sizes, however, showed that short -day (diapause-destined) individuals lay down the same proportion of f at as long-day (non-diapause) individuals, and the same proportion of fat across all size classes. The possible functional significance of t his phenomenon is discussed.