VENTURIA-CANESCENS PARASITIZING GALLERIA-MELLONELLA AND ANAGASTA-KUEHNIELLA - DIFFERING SUITABILITY OF 2 HOSTS WITH HIGHLY VARIABLE GROWTH-POTENTIAL

Venturia canescens (Grav.) (Hymenoptera: Ichneumonidae) is a solitary larval koinobiont endoparasitoid, ovipositing in several larval instar s of different pyralid moth species that are pests of stored food prod ucts. After oviposition, the host larva continues to feed and grow for at least several days, the precise time doing so depending on the sta ge attacked. We examined the relationship between host stage and body mass on parasitoid development in late second to fifth instars of two hosts with highly variable growth potential: the wax moth, Galleria me llonella (L) and the flour moth, Anagasta kuehniella (Zeller)(Lepidopt era: Pyralidae). C. mellonella is the largest known host of V. canesce ns, with healthy larvae occasionally exceeding 400mg at pupation, wher eas those of A. kuehniella rarely exceed 40 mg at the same stage. Para sitoid survival was generally higher in early instars of G. mellonella than in later instars. By contrast, percentage adult emergence in A. kuehniella was highest in late fifth instar and lowest in late second instar. A. kuehniella was the more suitable host species, with over 45 % adult emergence in all instars, whereas in G. mellonella we found le ss than 35% adult emergence in ail instars. Adult parasitoid size incr eased and egg to-adult development time decreased in a host size-and i nstar-specific manner from A. kuehniella. The relationship between hos t size and stage and these fitness correlates was less clear in G. mel lonella. Although both host species were parasitized over a similar ra nge of fresh weights, the suitability weight-range of A. kuehniella wa s considerably wider than G. mellonella for the successful development of V. canescens. However, in hosts of similar weight under 5 mg when parasitized, larger wasps emerged from G. mellonella than from A. kueh niella. Parasitoid growth and development is clearly affected by host species, and we argue that patterns of host utilization and resource a cquisition by parasitoids have evolved in accordance with host growth potential and the nutritional requirements of the parasitoid.