Hyperparasitoid volatiles as possible foraging behaviour determinants in the aphid parasitoid Aphidius uzbekistanicus (Hymenoptera : Aphidiidae)

The foraging behaviour of individual females of Aphidius uzbekistanicus Luz hetski (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 conditi ons when individual hyperparasitoid females, Alloxysta victrix Westwood (Hy menoptera: Alloxystidae) or their volatiles 6-methyl-5-hepten-2-one or a mi xture of iridoid substances soaked on vermiculite dummies were present simu ltaneously. Patch residence times of foraging primary parasitoid females we re significantly reduced in all analysed treatment groups. Attack numbers o n aphids and resulting aphid mummies were also significantly reduced. The p resence of hyperparasitoids or their volatiles had no influence on the prop ortion of time spent engaged in different behaviour by fie primary parasito id. After encounters with hyperparasitoid females or vermiculite dispensers , which had been soaked with the synthetical iridoids, A. uzbekistanicus fe males changed their behaviour more frequently, and they left the aphid colo ny at a higher rate than in the controls, where dispensers had been soaked with only pure pentane. The identification of the associated iridoidsubstan ces, produced in the hyperparasitoid mandibular glands, is briefly describe d and their biological significance is discussed.