The alfalfa weevil, Hypera postica Gyllenhal (Coleoptera: Curculionidae), is a major pest of alfalfa hay and seed production in North America. While chemical control methods can be effective, insecticide resistance has become a concern, and they can have negative impacts on non-target species including natural enemies and pollinators. Two European parasitoids, Bathyplectes curculionis Thomson (Hymenoptera: Ichneumonidae) and Oomyzus incertus Ratzeburg (Hymenoptera: Eulophidae), offer a potential alternative biological control strategy, but their prevalence in western Canada remains poorly understood. Traditional detection methods by live larval rearing, can have limited accuracy, particularly for parasitoid eggs and early instars. Here, we developed a novel multiplex PCR assay targeting the 5.8S ribosomal rDNA and ITS2 regions to detect B. curculionis and O. incertus within H. postica larvae. In 2020 and 2021, we assessed the parasitism rate of H. postica larvae from southern Alberta using both conventional live rearing (2021 only) and the multiplex PCR assay (2020–2021). Parasitism prevalence was significantly higher in 2021 (55.7%) compared to 2020 (6.9%), with multiparasitism changing little (10% to 11%). Live rearing predominantly detected B. curculionis , while O. incertus was nearly undetectable, whereas multiplex PCR revealed higher and more balanced parasitism prevalence for both parasitoid species. As susceptibility to parasitoids can differ between H. postica strains, we surveyed H. postica adults in Manitoba, Saskatchewan, and Alberta, and determined all were the western strain. These findings indicate that live rearing underestimates parasitism, confirm the dominance of the western strain in the Canadian prairies, and highlight the importance of molecular tools for host–parasitoid surveillance.
Diyes et al. (Mon,) studied this question.
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