Nectar provisioning close to host patches increases parasitoid recruitment,retention and host parasitism

In the adult stage, many parasitoids require hosts for their offspring growth and plant-derived food for their survival and metabolic needs. In agricultural fields, nectar provisioning can enhance biological control by increasing the longevity and fecundity of many species of parasitoids. Provided in a host patch, nectar can also increase patch quality for parasitoids and affect their foraging decisions, patch time residence, patch preference or offspring allocation. The aim of this study was to investigate the impact of extrafloral nectar (EFN) provisioning close to hosts on parasitoid aggregation in patches. The aphid parasitoid Diaeretiella rapae (M’Intosh) was released inside or outside patches containing Brassica napus L. infested by Brevicoryne brassicae L. aphids and Vicia faba L. with or without EFN. When parasitoids were released outside patches, more parasitoids were observed in patches with EFN than in patches deprived of EFN. This higher recruitment could be linked to a higher attraction of a combination of host and food stimuli or a learning process. A release–recapture experiment of labeled parasitoids released within patches showed the higher retention of parasitoids in patches providing EFN and hosts, suggesting that food close to the host patch affects patch residence time. Both attractiveness and patch retention could be involved in the higher number of parasitoids foraging in host patches surrounded by nectar and for the higher parasitism recorded. Nectar provisioning in host patches also affected female offspring allocation inside the patch.