Secondary host choice by the autoparasitoid Encarsia pergandiella

Autoparasitoids are species of parasitic wasps in the family Aphelinidae which produce females as solitary primary endoparasitoids of homopterans such as whitefly and scale insects ('primary hosts'), and males as solitary hyperparasitoids. Males generally develop on immature conspecific females or on individuals of other primary parasitoid species ('secondary hosts'). Encarsia pergandiella is an autoparasitoid that has been introduced to Italy for control of greenhouse whitefly Trialeurodes vaporariorum, in greenhouses and field crops. In this study we examined the secondary host selection behaviour of this species with regard to conspecific females and females of two thelytokous species, E. formosa and E. meritoria. Encarsia formosa has been used successfully for greenhouse whitefly control in Northern Europe, but has not been effective in Southern Italy in winter crops in unheated greenhouses. E. meritoria has recently spread in Italy, and may have potential for biological control of whitefly in the greenhouse environment. In the first experiment, female E. pergandiella were exposed to one of three pair-wise combinations of the three species in petri dish arenas. Parasitism was determined by dissection of the hosts. The number of hosts parasitized by E. pergandiella females did not differ with host species. However, significantly greater numbers of eggs were laid in E. meritoria in both treatments in which it was present; these hosts were more likely to be superparasitized. In a second experiment, observations of females in arenas with equal numbers of all three host species indicated that females encountered and parasitized all host species with approximately equal frequency, although the length of time females spent in the oviposition posture differed with host species.