No evidence for competition over floral resources between winter-active parasitoids and pollinators in agroecosystems

Warming temperate winters are resulting in increased insect winter activity. With modern agroecosystems largely homogenous, characterised by low floral diversity, competitive interactions may arise between flower-visiting species, with potential implications for the ecosystem services they provide (e.g. biological control and pollination). Flower strips may be implemented during winter months to support flower-visiting insects and enhance ecosystem service provision. Employing field trials conducted in Brittany, France between 2019 and 2021 and laboratory cage experiments, the current study examined the impact of winter flower strips on aphid biological control performed by parasitoid wasps and the potential for competitive interactions between winter-active parasitoids and pollinators. Results revealed that parasitism rate was not enhanced by the presence of winter flower strips. This lack of effect was not the consequence of pollinator presence, and the current study found no effect of pollinator abundance on parasitism rate. Flower strips may thus be implemented during winter months to support nectar-feeding insects when floral resources are scarce, with no evidence of exploitative competition between pollinators and parasitoids, nor a detrimental impact on biological control provision.