1Chemical Ecology Group, School of Chemistry and Physics, Keele University, Staffordshire, ST5 5BG, UK.
2School of Agriculture, Harper Adams University College, Newport, Shropshire, TF10 8NB, UK.
Commercially produced or naturally-occurring hymenopterous parasitoids can make a significant contribution to the control of pest aphids in both glasshouses and field crops. However, the efficacy of primary parasitoids is often undermined by high levels of attack from 'secondary' or hyperparasitoids. Despite the importance of hyperparasitoids in the population dynamics of aphids, relatively little is known of their host selection behaviour. However, recent studies undertaken at Harper of the hyperparasitoid Alloxysta victrix, have shown that females of this species have an innate ability to discriminate between unparasitized aphids (Myzus persicae) and those previously parasitized by the primary parasitoid Aphidius colemani. This ability to discriminate occurs through antennal contact with a potential host, and appears to be related to changes in the aphid cuticle as the primary parasitoid develops. The chemical changes in the cuticle of M. persicae following parasitism by A. colemani has also been investigated using gas chromatography-mass spectrometry (GC-MS) and the effect on A. vitrix of various hydrocarbon and triglyceride fractions has been assessed by contact bioassay.