The effect of host species on diapause induction in Nasonia vitripennis

The ‘expression’ of the photoperiodic clock in the parasitic wasp, Nasonia vitripennis, is modified by the species of blowfly puparia used as host. With Sarcophaga barbata the life-span is short and fecundity low, but the ‘switch’ to the production of diapause larvae occurs after only 8 to 11 short-day cycles; the proportion of diapause larvae in the progeny is consequently high. When puparia of Calliphora erythrocephala or Phormia terrae-novae are used as hosts, however, the wasps have a long life, a high fecundity but, since the ‘switch’ to diapause is delayed, a low proportion of diapause larvae in the progeny. Small puparia of S. barbata have a similar effect on life-span and fecundity but not on the ‘switch’ to diapause. The use of different hosts on alternate days produces a ‘zig-zag’ pattern of oviposition in which wasps appear less competent to deposit eggs in large Sarcophaga. One of the factors affecting life-span and fecundity is shown to be puparium thickness; that delaying the ‘switch’ when Calliphora or Phormia are used is probably a qualitative difference associated with the pupal and pharate adult haemolymph upon which the wasps feed.