Abstract
The use of nectar-providing plants to nourish natural enemies of pest species has become a widely-used approach in conservation biological control to reduce pest damage without the indiscriminate use of insecticides. Choice of plant species is crucial to maximize benefits, but suitable species are yet to be identified for many important crop-pest systems. Here we explored the suitability of three candidate nectar plants for use in brassica vegetables to suppress the globally significant pest, Plutella xylostella L. (Lepidoptera: Plutellidae), using the widely-distributed parasitoid, Cotesia vestalis (Haliday) (Hymenoptera: Braconidae). Volatiles of alyssum (Lobularia maritima (L.) Desv) (Brassicaceae) were attractive to the parasitoid and access to flowering shoots increased adult longevity and realized fecundity of C. vestalis. Moreover, adult diamondback moth derived no benefit from this flower. In contrast, buckwheat (Fagopyrum esculentum Moench) (Polygonaceae), a species widely used in conservation biological control in other systems, increased the longevity and fecundity of both pest and parasitoid, rendering it less suitable. A third plant, heronsbill (Portulaca grandiflora Hook.) (Portulacaceae) denied benefit to the pest and promoted longevity of the parasitoid under no-choice conditions but did not improve fecundity and was repellent to female parasitoids under choice conditions. The contrasting effects of this set of plants illustrate the need to test multiple response variables and effects on both pest and natural enemy when seeking optimal nectar plants for use in a novel conservation biological control system.