Host preferences of Aphidius (Hymenoptera: Aphidiidae) populations parasitising pea and cereal aphids (Hemiptera: Aphididae)

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Abstract
Laboratory studies were carried out on different populations of Aphidius ervi Hal., A. picipes (Nees) and A. rhopalosiphi De Stef. collected in England from Acyrthosiphon pisum (Harris), Sitobion spp., Microlophium carnosum (Buckt.) and Metopolophium dirhodum (Wlk.). When mated females from each population were confined separately with 4–5 other species of these and other genera, each population varied in their host preferences, even though individual populations of each species were electrophoretically and morphometrically homogeneous. These host preferences differed in terms of fecundity. Different populations of Aphidius ervi exhibited markedly different host ranges. This behaviour is probably conditioned rather than inherited, and its significance to biological control is discussed. The results suggest a need to assess quantitatively the effect of temperature, host size and host species on the parasitoids' ability to control pest aphids.