Plant functional traits drive landscape effects on biological pest control

Abstract: Parasitoid wasps that parasitize caterpillars can use herbivore-induced plant volatiles (HIPVs) to find their hosts. However, effects of HIPVs at the landscape scale are poorly studied, and it is unknown whether recruitment of parasitoids to crop fields from the broader landscape can be increased by HIPVs. In 19 different landscapes, we studied whether parasitism rates of Pieris brassicae caterpillars were influenced by plant traits associated with HIPV-mediated attraction of parasitoids. Additionally, we investigated whether the abundance of Brassicaceous species, providing alternative hosts for the parasitoids, affected the parasitism rates of P. brassicae caterpillars. Our data indicate that parasitism rates on the attractive cabbage accession Christmas Drumhead were generally higher than on the less attractive accession Badger Shipper. However, this accession effect was only observed in landscapes with a substantial cover of Brassicaceae and where parasitism rates were relatively high. Our study highlights the importance of plant functional traits as predictors of parasitism, and that these need to be considered within the landscape context.