Manipulation of parasitoid state influences host exploitation by Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae).

Jenner, W.H., Kuhlmann, U., Cappuccino, N., and Mason, P.G. (2012). "Manipulation of parasitoid state influences host exploitation by Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae).", Biological Control, 63(3), pp. 264-269. doi : 10.1016/j.biocontrol.2012.09.012  Access to full text

Abstract

In biological control programs, it should be possible to manipulate agents during host specificity trials so that they exhibit a lower host acceptance threshold. This would help to ensure that any non-target species that could be attacked in the field will also be attacked in the laboratory and flagged as potential hosts. The question is how to encourage agents to express the widest possible host range during trials. This study examined the effects of variation in parasitoid state (mating status, nutritional status, age, host experience) and the test environment (competition, arena size, presence of host-damaged leek leaves) on the degree of host exploitation by Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae). As a first step, this study looked for changes in oviposition by the parasitoid on its normal host, the leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae). Each of the seven factors was tested independently to assess its effect on the number of parasitoid offspring produced and host mortality. Previous host experience led to a marginal increase, while competition led to a per-capita decrease, in the degree of host exploitation. In contrast, mating status, arena size and the presence of host-damaged leek leaves had no measurable effects. Finally, parasitoid age and nutritional status had strong effects in the opposite direction to predictions, with younger and sugar-fed individuals exhibiting higher host exploitation than older and sugar-starved parasitoids, respectively. This study suggests that a sound understanding of species-specific reproductive biology and parasitoid-host interactions is likely required before oviposition-enhancing parasitoid states can confidently be identified.

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