Identifying Delia root maggots to aid vegetable seed growers in the PNW

Delia spp. (Diptera: Anthomyiidae), are a group of root-feeding maggots (fly larvae) impacting vegetable seed production, an $18.2M industry in Washington State. Adult flies lay eggs in the soil near germinating seeds so that hatching maggot may feed on developing seedlings. Planting time for vegetable seed crops is a critical, narrow window to achieve adequate temperatures for germination, avoidance of overly rainy conditions, and proper daylength for seed-set. While it is unlikely that growers will be able to adjust their planting dates based on pest status, the ability to predict the egg-laying window of Delia flies would help growers manage their risk precisely and conservatively, by either omitting or including an insecticide at seeding if planting times overlap (or not) with egg-lay. Degree day models exist for key Delia species to the PNW, but these models are not widely used due to development and validation east of the Continental Divide. Our project will validate phenology models for the top two Delia pests in the PNW (seedcorn maggot and cabbage maggot), identifying flies to species with molecular techniques, and test if model-predicted oviposition time can be used for to guide management.