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.
Highlights
Intensive agricultural monocultures and simple agricultural landscapes do not provide natural enemies with favorable resources and conditions[1,2,3]
We tested three flowering plants under laboratory conditions, including a long-inflorescence, heronsbill (Portulaca grandiflora Hook.) (Portulacaceae), a perennial that can grow under adverse conditions[53], alyssum (Lobularia maritima (L.) Desv) (Brassicaceae) and buckwheat (Fagopyrum esculentum Moench) (Polygonaceae)
All plants with flowers tested in this experiment significantly increased the adult longevity of both male and female C. vestalis compared with plants without flowers and the water control
Summary
Intensive agricultural monocultures and simple agricultural landscapes do not provide natural enemies with favorable resources and conditions[1,2,3]. The addition of flowering plants within or around crop fields can enhance the impact of natural enemies by providing nectar, pollen[10,11,12], alternative hosts or prey[13], favorable microclimatic conditions[14] and shelter[1,15,16]. Nectar from flowering plants is an important supplementary food which can increase parasitoid longevity and favor biological control[17,18]. Lack of supplemental food for C. vestalis in the field and intensive farming practices make it valuable to develop conservation biological control strategies to increase its efficiency against P. xylostella. The hypotheses of the present study were that (1) flowering plants differ in the extent of benefit afforded to P. xylostella and C. vestalis; (2) the attractiveness of flowering plants does not necessarily correlate with the performance of C. vestalis on these flowering plants
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