Syrphid Diversity in Sweet Alyssum Flower Strips in Quebec's Lettuce Fields: Molecular Identification and Delimitation of the <i>Sphaerophoria</i> Complex

Lettuce is an economically significant crop in Canada, with 70% of commercial production occurring in peatlands (Histosols) in southern Quebec. Insecticide application is currently the main method for managing lettuce pests, but there is a growing need for sustainable pest control alternatives. Conservation biological control, such as incorporating flowering strips into fields to attract natural enemies, is a promising strategy. This study evaluates the potential of sweet alyssum, <i>Lobularia maritima</i>, to attract syrphids, whose larvae are voracious predators of lettuce pests, particularly aphids. A total of 16 species were collected from flowering plants across three lettuce farms in Quebec. The most abundant species was <i>Toxomerus marginatus</i>, accounting for 70% of all specimens, followed by <i>Sphaerophoria philanthus</i> (10.3%) and <i>Allograpta obliqua</i> (4.6%). All other species each constituted less than 4% of the total catch. A subset of 82 females from the <i>Sphaerophoria philanthus/asymmetrica/abbreviata</i> species complex underwent COI DNA-based delimitation analyses, revealing three molecular operational taxonomic units (MOTUs). Fourteen of the 16 identified species or MOTUs are aphidophagous. Analysis of diversity metrics across the three sites indicated no statistically significant differences between flower and control treatments. However, of the 16 species recorded, 10 were found exclusively or predominantly (≥ 80%) in flower plots. Our findings suggest that alyssum flowers can successfully attract natural aphid predators in lettuce fields. This approach has the potential to mitigate lettuce pest issues and reduce reliance on insecticides, thus promoting more sustainable pest management.