Sugar feeding by parasitoids inside and around vineyards varies with season and weed management practice

Abstract

Feeding on sugar-rich resources dramatically prolongs lifespan and increases foraging performance in most parasitoids. The physiological and fitness effects of sugar feeding were studied in many parasitoid species under lab conditions, but far fewer studies examined them in the field. Even less is known about the environmental conditions that affect the prevalence of sugar feeding in natural parasitoid communities. Such information can guide planning of suitable habitats for these important biological control agents. We compared sugar feeding frequencies in parasitoid communities along four seasons, in wine-producing vineyards and in nearby natural plots, using qualitative anthrone tests. We also tested how the vineyards’ weed management practice (mechanical trimming or herbicide application) affected the parasitoids’ sugar feeding rates. Sugar feeding was significantly more common in the natural areas compared to the vineyards in all seasons. Sugar feeding rates were highest during spring and lowest in the winter. They were not consistently affected by weed management treatment, but increased with the number of flowering plant species, especially in spring. Our results suggest that parasitoids are limited by sugar sources in agricultural plots even when undisturbed by farming activities (during winter in our case), and that 'softer' weed management treatments do not necessarily improve their prospects for sugar feeding. A more targeted approach, of planting or preserving a higher richness of flowering plants throughout the seasons, may provide parasitoids with more sugar sources and thus support them in agricultural plots.