D3420: Effects of cabbage maggot diet on longevity, fecundity and egg laying frequency

The cabbage maggot, Delia radicum (Diptera: Anthomyiidae) is the most destructive pest of Brassicaceous vegetables in the Willamette Valley, Oregon, USA, and growers lack management tools. Here, we investigate how nutrient deficiencies affect fecundity of cabbage maggot, with the goal of exploiting sensitive insect stages to design a field trapping system. Prior research from Great Britain and Russia suggests adult females develop a first egg batch using amino acid reserves acquired as larvae, but subsequent egg batches require provisioning with additional protein, a potentially rare nutrient in agricultural settings. We conducted a laboratory assay to compare how diet and mating status affect cabbage maggot fecundity in an Oregon-based population. Specifically, we compared daily egg counts among four treatments: (1) mated females fed sugar, protein, and water [“Full Diet Mated” (FDM)]; (2) unmated flies fed the full diet (“Full Diet Unmated” [FDU]); (3) mated flies fed protein and water only [“Sugar Starved” (SS)], and (4) mated flies fed sugar and water only [“Protein Starved” (PS)]. Fecundity was highest for the FDM treatment and lowest for FDU. Protein and sugar starvation each reduced fecundity compared with FDM, and protein deprivation reduced the frequency with which eggs were laid. Sugar, but not protein, starvation reduced adult longevity. Next steps in building a cabbage maggot Integrated Pest Management program include estimating nutrient access in the field and evaluating proteinaceous lures and trap placement as part of a bait and kill trapping approach.