Presence and Distribution of Alfalfa Weevil and Sitona Species in Alfalfa Fields Grown for Seed in Alberta
Creators: Chennamkulangara, Priyatha
Publisher: name: University of Alberta Library
Year: 2024

<p>The alfalfa weevil (Hypera postica (Gyllenhal), Curculionidae: Coleoptera) is a major pest of alfalfa (Medicago sativa L., Fabaceae) that feeds on alfalfa foliage. High density larval populations cause significant damage through leaf skeletonization. This study examines the location of adult alfalfa weevil in alfalfa fields grown for seed at various times throughout the growing season using different sampling techniques. A secondary objective is to assess the diversity and abundance of broad nosed weevils (Sitona spp. (Curculionidae: Coleoptera)) in these same fields. The study was conducted in 18 alfalfa fields grown for seed in southern Alberta over three growing seasons (2021-2023) with two fields from 2021 repeated in 2022. Alfalfa fields were sampled using various capture methods to monitor flying weevils and those present on the ground and plant. <br>
Five fields with established alfalfa stands grown for seed were selected in 2021 and 2022 and eight fields in 2023. Alfalfa weevils captured in emergence cages, pitfall traps, sweep net samples and soil samples were collected in all the study years. Additionally, double-sided sticky cards and malaise traps were used in 2021 to capture flying alfalfa weevils. In 2022, trials using water traps and baited pitfall traps tested the attractiveness of alfalfa weevil to water and putative pheromone components ((Z)- and (E)-3,3-dimethylcyclohexane- ∆ 1, α-acetaldehyde (1:1)) and the aggregation pheromone of the pea leaf weevil (4-methyl-3,5 heptanedione). In 2023, solo cup pitfall traps were replaced with directional pitfall traps separated by a barrier to determine the directionality of walking alfalfa weevils. In 2023, the effect of alfalfa stand age on weevil abundance was tested.<br>
Sweep samples were an effective tool for capturing and monitoring adult alfalfa weevils, and also predicted subsequent larval densities. Adult alfalfa weevils were captured in low numbers in pitfall traps, water traps positioned on the ground and in soil samples taken at various times throughout the season. Sticky cards and malaise traps failed to capture any flying alfalfa weevils, indicating less reliance on flight for dispersal by alfalfa weevils. More adult alfalfa weevils were captured in emergence cages positioned outside alfalfa fields than in those positioned within, revealing that some adult alfalfa weevils overwinter outside the field. Pitfall traps (2022) baited with pea leaf weevil aggregation pheromone attracted numerically but not statistically more alfalfa weevil adults than traps baited with putative alfalfa weevil pheromone components or solvent only control traps. More female alfalfa weevils were consistently captured than male alfalfa weevils in the overwintered generation collected in the spring during the three experimental years. More overwintered alfalfa weevil adults were collected from mature than young alfalfa stands, suggesting the preference for or lack of dispersal from established alfalfa fields by adult alfalfa weevils. Weekly average temperature and relative humidity affected the number of alfalfa weevil adults that were captured in sweep samples.<br>
Other weevil species including Sitona spp. were collected consistently using various sample methods. Two species of broad-nosed weevils were identified from the by-catch of sweep net samples, the alfalfa curculio (Sitona lineellus Bonsdorff) and to a lesser extent the pea leaf weevil (Sitona lineatus L.), in addition to non-Sitona weevil species. <br>
Overall, the current research has identified effective monitoring tools for alfalfa weevil adults, the abundance of alfalfa weevil throughout the growing season and potential overwintering locations of adult alfalfa weevils. The common occurrence of alfalfa curculio in alfalfa fields grown for seed highlights the need for more research on this species in Alberta.</p>