AUTHOR=Afentoulis Dimitrios G. , Cusumano Antonino , Greenberg Liana O. , Caarls Lotte , Fatouros Nina E. 

TITLE=Attraction of Trichogramma Wasps to Butterfly Oviposition-Induced Plant Volatiles Depends on Brassica Species, Wasp Strain and Leaf Necrosis

JOURNAL=Frontiers in Ecology and Evolution

VOLUME=9

YEAR=2021

URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2021.703134

DOI=10.3389/fevo.2021.703134

ISSN=2296-701X

ABSTRACT=<p>Within the Brassicaceae, wild as well as crop species are challenged by specialist herbivores including cabbage white butterflies (<italic>Pieris</italic> spp.). The wild crucifer <italic>Brassica nigra</italic> responds to oviposition by <italic>Pieris</italic> butterflies by the synergistic expression of two egg-killing traits. Genotypes that express a hypersensitive response (HR)-like necrosis (direct egg-killing) also emit oviposition-induced plant volatiles (OIPVs) attracting <italic>Trichogramma</italic> egg parasitoids (indirect egg-killing). This so-called double defense line can result in high butterfly egg mortalities. It remains unknown whether this strategy is unique to <italic>B. nigra</italic> or more common in <italic>Brassica</italic> species. To test this, we examined the response of different <italic>Trichogramma evanescens</italic> lines to OIPVs emitted by <italic>B. nigra</italic> and three close relatives (<italic>Brassica napus, Brassica rapa</italic>, and <italic>Brassica oleracea</italic>). Furthermore, we evaluated whether HR-like necrosis played a role in the attraction toward plant volatiles. Our results show a specificity in wasp attraction to different plant species. Three out of four plant species attracted a specific <italic>T. evanescens</italic> strain, including the crops <italic>B. rapa</italic> and <italic>B. napus</italic>. Parasitoid attraction was positively affected by presence of HR-like necrosis in one plant species. Our findings imply that, despite being a true generalist in terms of host range, <italic>T. evanescens</italic> shows intraspecific variation during host searching, which should be taken into account when selecting parasitoid lines for biocontrol of certain crops. Finally, we conclude that also crop plants within the Brassicaceae family possess egg-killing traits and can exert the double-defense line which may enable effective selection of egg-killing defense traits by cabbage breeders.</p>