Molecular markers for Diadegma (Hymenoptera: Ichneumonidae) species distinction and their use to study the effects of companion plants on biocontrol of the diamondback moth
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Molecular markers facilitate the quantification of parasitization of pest species and the distinction of related parasitoid species. We designed new markers that allow the distinction of often misidentified Diadegma semiclausum and D. fenestrale parasitization in field-collected diamondback moth (Plutella xylostella) larvae. The markers were applied to study if cornflower (Centaurea cyanus) companion plants increase parasitization of the diamondback moth by Diadegma parasitoids in cabbage fields, as they do in the Mamestra brassicae—Microplitis mediator pest-parasitoid pair. Among 1708 P. xylostella larvae analyzed, we found a high parasitization rate (72.2 % total, 41.7 % by D. semiclausum, 24.9 % by D. fenestrale, 5.6 % by both), but no significant effects of cornflower presence. Our results highlight the need for species-specific markers and the specific action of companion plants. To increase natural control in crop fields, habitat management needs to be tailored to—and acts on—specific target species.
KeywordsParasitic wasp Mitochondrial COI Diagnostic multiplex PCR Species-specific marker Biological control Plutella xylostella Diadegma semiclausum Diadegma fenestrale
We thank all farmers for making their fields available, K. Oude-Lensferink, J. Preukschas, A. Moesch, D. Eglin, G. Förderer, M. Fürst and C. Gerber for help with field work, in the laboratory and during analyses, F. Ronco, for help with statistics, and Sebastian Gygli for proof-reading the manuscript. The project was supported by the Singenberg Foundation, the Bristol Foundation, the Federal Office for the Environment, the Parrotia-Foundation, the Werner Steiger Foundation, the Ernst Göhner Foundation, the Stiftung zur internationalen Erhaltung der Pflanzenvielfalt, Schöni Swissfresh AG and the Spendenstiftung Bank Vontobel.
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