Selective flowers to enhance biological control of cabbage pests by parasitoids

Habitat management is an important element in sustainable agriculture and can be used to maximize a range of ecosystemservices that support crop production. An important example of such ecosystem services is biological control of pests whichcan be enhanced by providing arthropod natural enemies with suitable floral resources. The potential risk of this approach,however, is that flowering plants may enhance the fitness of the targeted pests as well. We conducted experiments to identifyselective plant species that would improve the longevity and parasitization rate of the parasitoid wasp Microplitis mediatorwithout benefiting its host pest, the cabbage moth Mamestra brassicae. Effects on longevity were also assessed for Diadegmafenestrale, a generalist parasitoid wasp attacking lepidopteran pests. Additionally, we compared the effects of floral and extrafloralnectar, the latter being formed in some plant species and can significantly prolong the duration of nectar availability for naturalenemies. Longevity of M. mediator and D. fenestrale as well as parasitization rates of M. mediator were significantly increasedby the presence of Fagopyrum esculentum (floral nectar), Centaurea cyanus (floral and extrafloral nectar) and non-floweringVicia sativa (extrafloral nectar). M. mediator parasitized 202.3±29.7 M. brassicae larvae during its lifetime when presented F.esculentum, compared to 14.4±3.4 larvae in the absence of floral resources. Extrafloral nectar of C. cyanus and V. sativa was assuitable for M. mediator as floral nectar and significantly increased longevity and parasitization rates. Longevity and fecundityof M. brassicae were not supported by the plant species tested. These results stress the importance of plant screening to achieveplant selectivity and to maximize biological control. F. esculentum, C. cyanus and V. sativa are recommended as selective plantspecies to enhance parasitoids of M. brassicae.