Effect of extrafloral nectar provisioning on the performance of the adult parasitoid Diaeretiella rapae

Abstract

Plant derived-food is an important food source for natural enemies. We conducted laboratory tests to evaluate the suitability of extrafloral nectar (EFN) from Vicia faba as a potential food source for female Diaeretiella rapae in an intercropping context, and how EFN affects the survivorship and progeny production in this species. Extrafloral and floral nectar have a similar sugar composition, a highly nutritious food for parasitoids. Under controlled conditions, intercropping V. faba with Brassica oleracea had no impact on V. faba EFN sugar composition. Female parasitoids lived significantly longer when provided with EFN (14days) than when provided with water (4days), honeydew (4days), and honey and water (9days) or when they were without food (3days). The longevity of females provided with EFN did not differ in the absence or presence of aphids. The numbers of hosts parasitised and offspring produced per female over the course of her lifespan were significantly increased by placing a V. faba plant next to a B. oleracea plant. However, this increase was observed for both nectary-bearing and nectary-less V. faba plants. Feeding on EFN resulted in an increase in the length of the oviposition period, which was primarily concentrated during the first four days of the life of the female. No impacts of V. faba EFN provision were observed on offspring larval survival, sex ratio or size. These results suggest that provision of EFN can increase both the rate of parasitism and parasitoid survival without hosts.