Extrafloras and floral nectar promote biocontrol services provided by parasitoid wasps to rice crops

Intensive crop production often requires the use of significant amounts of chemical fertilizers and pesticides, leading to negative environmental impacts. Strategies to increase agricultural productivity to meet future demands for food should therefore involve the promotion of ecosystem services, rather than the use of synthetic inputs. Sowing nectar-rich flowering plants is an important strategy in conservation biological control that can increase the fitness of the natural enemies of crop pests. In the present study, we conducted lab-based experiments to assess the benefits of passion fruit (Passiflora edulia) and lemon basil (Ocimum basilicum var. citriodorum) as nectar sources for six parasitoid wasp species that are key natural enemies of rice pests. We also examined the potential of these two plants to enhance biocontrol services by parasitoid wasps when planted on the bunds of subtropical rice fields. In the laboratory, both plants and especially passion fruit increased parasitoids’ longevity and fecundity. Both plants also increased field abundance of parasitoid wasps and slightly increased pest control services, as shown by a lower herbivorous insects to parasitoid wasps ratio, although pest numbers remained high. This study contributes important new information for ecological intensification in rice cropping systems and should guide the selection of optimal nectar plants to promote biological control services.