Assessing alfalfa weevil parasitoid prevalence in alfalfa seed production fields in Alberta, Canada

Alfalfa, Medicago sativa (L.) (Fabales: Fabaceae), is an excellent source of high protein feed for livestock. Canada is the second largest producer of alfalfa seed (4.2 M Kg/year) in the world, with the vast majority of production concentrated in the province of Alberta. The productivity of these seed fields is threatened by an invasive insect, the alfalfa weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae). Feeding by alfalfa weevil larvae can result in substantial loss of foliage and can severely reduce alfalfa yield. Recently, insecticide resistance was confirmed in several alfalfa weevil populations in Alberta, and few other management options exist. Biological control agents of alfalfa weevil are present in Alberta including the parasitoids, Bathyplectes curculionis (Thomson) (Hymenoptera: Ichneumonidae) and Oomyzus incertus (Ratzeburg) (Hymenoptera: Eulophidae); however, the distribution of these species and their parasitism levels are currently unknown. Here, we assessed the distribution and parasitism levels of B. curculionis and O. incertus throughout southern Alberta. A survey was conducted to collect alfalfa weevil larvae from seed production fields in 2020 and 2021 and a multiplex PCR assay was developed to identify the parasitoids within weevil larvae. Parasitism levels based on the multiplex PCR assay were comparable to live rearing and ranged from 11.1-60.1 % across sites. In addition, alfalfa weevil larval samples were collected throughout the growing season to assess the activity period of these parasitoids. Assessing when and where these parasitoids occur will allow growers to better utilize these biological control agents and, ultimately, reduce spray applications