Abstract
Parasitoid wasps contribute to biological control services. Parasitoid adults are highly dependent on sugar-rich resources. Adding flowering plants providing nectar in crop fields promotes parasitoid wasps, but not always pest parasitism because addition of flowering plants may attract parasitoid species that are not directly involved in the control of crop pests.
In a factorial experiment conducted for one year in pesticide-free orchards, we analysed the effects of three common plant species (Capsella bursa-pastoris Medik., Veronica persica Poir. and Vicia sativa L.) in association with apple trees on parasitoid wasp recruitment and parasitism of one major apple pest, Dysaphis plantaginea (Passerini). We combined morphological and molecular identifications to characterize the parasitoid communities associated with each plant species.
Parasitoid communities were different between plant species. Plant effects on the abundance of the parasitoid wasps did not depend on the amount of floral resources provided by the tested plants. Over the whole season, the parasitoid wasp species Ephedrus persicae (Froggatt) and Aphidius matricariae (Haliday) involved in D. plantaginea parasitism accounted for 6% of the total parasitoid abundance and were mainly associated with V. persica plots. We observed a higher parasitism rate in apple trees associated with V. persica and a lower number of aphid colonies in apple trees associated with V. sativa. However, plant treatments had no effect on the abundance of D. plantaginea or on generalist predators and ant occurrences in aphid colonies. As a result, the three plants tested had a limited impact on the rosy apple aphid (RAA) regulation overall.
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