Seasonal changes in aphid hyperparasitoid occurrence in sweet pepper and raspberry in Belgium

By attacking primary parasitoids, hyperparasitoids represent a major threat to biological pest control, especially in the context of aphid control which relies to a large extent on parasitoids. Despite their importance still little is known about when hyperparasitoids arrive in the crop, their diversity, how hyperparasitoid communities change throughout the growth season and whether these changes are similar across different crop species. Here, we used banker plants with aphids parasitized by the commonly applied biocontrol agent Aphidius ervi to detect and identify hyperparasitoids in five sweet pepper and five raspberry farms in Flanders, Belgium. Surveys started early in the growth season (March) and lasted until October. Throughout the survey, hyperparasitoid species from six different genera were found. Hyperparasitoids were observed from the start of the survey until September in sweet pepper and until October in raspberry. However, the overall observed rate of hyperparasitism within the banker plants was higher in sweet pepper (42%) than in raspberry (10%). The most commonly identified genus differed between the two crops. Dendrocerus was the most frequently identified hyperparasitoid in raspberry throughout the entire season. Conversely, while Dendrocerus was the only hyperparasitoid genus found in March and April in sweet pepper, it became replaced by individuals of the genera Alloxysta, Pachyneuron and Phaenoglyphis later in the growth season. The presence of multiple species of hyperparasitoids in a single crop reinforces their potential to disrupt biocontrol programs. Therefore, future efforts should focus on the development of effective management strategies to control hyperparasitoids.