Attract and reward: combining chemical ecology and habitat manipulation to enhance biological control in field crops

1. An increase in pesticide resistance in many pest species is promoting interest in biological control.Much remains to be learned about natural enemy immigration into and persistence withincrops at specific times and how to maximize suppression of pest populations. Therefore this studywas conducted to test a novel biological control approach, 'attract and reward' which combines twoaspects of applied insect ecology: synthetic herbivore-induced plant volatiles (HIPVs) to improveimmigration of beneficial taxa into crops and nectar plants to maintain their populations.2. The 'attract and reward' approach was tested in sweetcorn, broccoli and wine-grapes withseveral HIPV formulations at 1Æ0% (v ' v) as attractants and buckwheat (Fagopyrum esculentumMoench) as reward. Abundance of insects was assessed with non-attractive sticky traps for up to22 days after the HIPV spray application.3. In sweetcorn, Eulophidae were more numerous in the attract treatments: methyl anthranilate,methyl jasmonate (MeJA), methyl salicylate (MeSA) and HIPV mix. Encyrtidae were more abundantnear MeJA-treated plants. In broccoli, Scelionidae were more abundant in MeSA treatmentswith reward and near cis-3-hexenyl acetate-treated plants without reward whilst Ceraphronidaewere more numerous near MeSA and predators were more abundant near HIPV mix-treatedplants.Nectar plant reward increased catches of parasitoids from several families in all three testedcrop species and increased predators in sweet corn and broccoli.4. Increases in natural enemy numbers were correlated with effects at the first and second trophiclevels. Significantly fewer larvae of the sweetcorn pest Helicoverpa spp. were found on sweetcornplants from plots with reward and significantly less Helicoverpa spp. damage was evident to cobsfor one of theHIPV treatments.5. Synthesis and applications. Results suggest that applications of synthetic HIPVs can enhancerecruitment of natural enemies and buckwheat was a suitable resource subsidy plant for increasingabundance and residency. Whilst both of these approaches offer potential to enhance biologicalcontrol, further work is required to realize fully synergistic effects from their combination as an'attract and reward' approach.