THE PERCEPTION OF GENETIC SIMILARITY BY THE SOLITARY PARTHENOGENETIC PARASITOID VENTURIA-CANESCENS, AND ITS EFFECTS ON THE OCCURRENCE OF SUPERPARASITISM

Observations of oviposition patterns adopted by uniparental lines of t he solitary parthenogenetic endoparasitoid Venturia canescens Gravenho rst (Hymenoptera: Ichneumonidae) reveal that the occurrence of superpa rasitism is influenced by the genealogical relationship between adult wasps and conspecific progeny which they encounter within parasitized hosts (larvae of the Indian meal moth Plodia interpunctella Hubner (Le pidoptera: Pyralidae)): the closer the relationship, the lower the occ urrence of superparasitism. This behaviour has an adaptive interpretat ion because it allows Venturia to avoid selective penalties incurred w hen larval offspring compete with genetically similar progeny. Venturi a's ability to discriminate between her own eggs, those of her relativ es, and those of other conspecifics is mediated by a chemical marker p roduced by Dufour's gland, an accessory of the adult female's reproduc tive system. This conclusion is supported by chemical analyses which r eveal that, while Dufour's glands from unrelated females show highly s ignificant variation between the spectra of volatile hydrocarbons cont ained in their respective secretions, closely-related females show neg ligible differences in their chemical constitutions. These findings le nd further weight to current theory that superparasitism can be delibe rately deployed as an adaptive part of a wasp's behavioural repertoire , and also identify the physiological mechanism by which such an ovipo sition response may be achieved.