Distribution and parasitism rate of cabbage seedpod weevil parasitoids over almost a decade in Quebec (Canada)

The cabbage seedpod weevil (CSW), a pest of oilseed rape crops, was first detected in the Province of Quebec (Canada) in canola in 2000. The parasitoid wasp Trichomalus perfectus is the main biological control agent of the CSW in Europe. However, its efficiency as well as its distribution across the province of Quebec are poorly known. We investigated CSW damage in canola fields, along with the abundance and parasitism rates of all its parasitoids, as well as that of T. perfectus alone, in Quebec from 2012 to 2020. This study highlighted that the CSW is well established in Quebec (82% of canola fields sampled), especially in the regions of Bas-Saint-Laurent, Chaudière-Appalaches, and Capitale-Nationale. Only three fields exceeded the threshold of 25% damaged pods, and only in 2019. Parasitoids of CSW were present in 62% of canola fields. Their distribution follows that of the CSW and their populations were primarily composed of Pteromalidae (95.7% of the individuals) among which T. perfectus was the main species with almost 80% of the individuals. The mean parasitism rate from 2012 to 2020 was 43.1% and that of T. perfectus was 26.1%. Seed damage was reduced by 47% on average when CSW larvae were parasitized. Parasitoids, particularly T. perfectus due to its higher abundance compared to other parasitoid species and its significant contribution to the overall parasitism rate, play a key role in controlling CSW populations in Quebec, helping to keep them below the economic damage threshold. • Parasitoids of the cabbage seedpod weevil (CSW) were found in 62% of canola fields. • Parasitoids were mainly Pteromalidae (95.7%), mostly Trichomalus perfectus (78.8%). • Parasitism rate from 2012 to 2020 was 43.1% and that of T. perfectus was 26.1%. • Seed damage decreased by about 47% when CSW larvae were parasitized. • Parasitoids, especially T. perfectus , help keep CSW below the damage threshold.