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Abstract
The foraging behaviour of individual females of Aphidius uzbekistanicus Luzhetski (Hymenoptera: Aphidiidae) on oat plants with one colony of the grain aphid Sitobion avenae F. (Homoptera: Aphididae) was examined in laboratory experiments. Patch time allocation was analysed under semi-natural conditions when individual hyperparasitoid females, Alloxysta victrix Westwood (Hymenoptera: Alloxystidae) or their volatiles 6-methyl-5-hepten-2-one or a mixture of iridoid substances soaked on vermiculite dummies were present simultaneously. Patch residence times of foraging primary parasitoid females were significantly reduced in all analysed treatment groups. Attack numbers on aphids and resulting aphid mummies were also significantly reduced. The presence of hyperparasitoids or their volatiles had no influence on the proportion of time spent engaged in different behaviour by the primary parasitoid. After encounters with hyperparasitoid females or vermiculite dispensers, which had been soaked with the synthetical iridoids, A.uzbekistanicus females changed their behaviour more frequently, and they left the aphid colony at a higher rate than in the controls, where dispensers had been soaked with only pure pentane. The identification of the associated iridoid substances, produced in the hyperparasitoid mandibular glands, is briefly described and their biological significance is discussed.
Highlights
The host searching behaviour of parasitoids can be influenced by a variety of different clues (Quicke, 1997). Vet & Dicke (1992) emphasized the important role of infochemicals as determinants for parasitoid behaviour
As the reproductive success of aphid primary parasitoids is predominantly determined by their foraging decisions, hyperparasitism may have had a decisive effect on the evolution of their foraging strategies (Mackauer & Völkl, 1993; Weisser, 1994)
Based on our results it can be concluded that the hyperparasitoid A. victrix exerts a certain influence on the searching behaviour of A. uzbekistanicus females
Summary
The host searching behaviour of parasitoids can be influenced by a variety of different clues (Quicke, 1997). Vet & Dicke (1992) emphasized the important role of infochemicals as determinants for parasitoid behaviour. The foraging decisions of aphid parasitoids on the plant include physiological factors such as the egg load of the searching female (Collins & Dixon, 1986), starvation (Grasswitz & Paine, 1993), age (Weisser, 1994) and mating status (Michaud, 1994). In accordance with Waage’s patch-leaving decision rule (Waage, 1979), both last men tioned factors can lead to extended search in aphid colo nies (Budenberg, 1990; Ahmad, 1994), whereas encounters with already parasitized hosts may lead to reduced patch residence times, as shown by van Lenteren (1991) for Leptopilina heterotoma (Thomson), a Droso phila parasitoid
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