In-Field <i>Diadegma insulare</i> (Cresson) (Hymenoptera: Ichneumonidae) Parasitism Rates of <i>Plutella xylostella</i> (L.) (Lepidoptera: Plutellidae) in Virginia Cole Crops

Abstract

The diamondback moth, Plutella xylostella (L.), is a significant pest of brassica crops that is found across the globe. Due to the development of insecticide resistance, control tactics have shifted focus towards integrating pest management techniques such as biological control. Diadegma insulare (C.), Oomyzus sokolowskii (K.), and Microplites plutellae (M.) are parasitoids of P. xylostella found in the Eastern United States. From 2022 to 2025, we surveyed P. xylostella larvae and pupae in locations across Virginia to assess the current rates of parasitism in brassica fields. Specimens were brought to the laboratory and reared to assess parasitoid emergence rates. Only D. insulare specimens were found during the study. Adult P. xylostella, larvae and pupae, adult D. insulare, D. insulare pupae, unknown parasitoids, and unknown deaths were recorded and used to calculate the rates of parasitism at each location. We concluded that the parasitism rate varied by location and year, which was expected due to regional conditions and seasonality. Rates averaged between 30.1 and 65% by year, with the lowest individual rate being 15% in 2025 and the highest at 100% in 2022. This suggests that D. insulare is actively present in Virginia and could be a successful biological control agent when paired with other integrated pest management techniques to reduce P. xylostella populations.