Herve, M. | Search bioRxiv

bioRxiv2019

Plant defense resistance in natural enemies of a specialist insect herbivore

Plants defend themselves against herbivores through the production of toxic and deterrent metabolites. Adapted herbivores can tolerate and sequester these metabolites, allowing them to feed on defended plants and become toxic to their own enemies. Can herbivore natural enemies overcome sequestered plant defense metabolites to prey on adapted herbivores? To address this question, we studied how entomopathogenic nematodes cope with benzoxazinoid defense metabolites that are produced by grasses and sequestered by a specialist maize herbivore, the western corn rootworm. We find that nematodes from US maize fields in regions in which the western corn rootworm was present over the last 50 years are behaviorally and metabolically resistant to sequestered benzoxazinoids and more infective towards the western corn rootworm than nematodes from other parts of the world. Exposure of a benzoxazinoid-susceptible nematode strain to the western corn rootworm for five generations results in higher behavioral and metabolic resistance and benzoxazinoid-dependent infectivity towards the western corn rootworm. Thus, herbivores that are exposed to a plant defense sequestering herbivore can evolve both behavioral and metabolic resistance to plant defense metabolites, and these traits are associated with higher infectivity towards a defense sequestering herbivore. We conclude that plant defense metabolites that are transferred through adapted herbivores may result in the evolution of resistance in herbivore natural enemies. Our study also identifies plant defense resistance as a novel target for the improvement of biological control agents.

plant biology↗

bioRxiv2019

Distinct defense strategies allow different grassland species to cope with root herbivore attack

O_LIRoot-feeding insect herbivores are of substantial evolutionary, ecological and economical importance. Plants can resist insect herbivores through a variety of tolerance and resistance strategies. To date, few studies have systematically assessed the prevalence and importance of these strategies for root-herbivore interactions across different plant species.\nC_LIO_LIHere, we characterize the defense strategies used by three different grassland species to cope with a generalist root herbivore, the larvae of the European cockchafer Melolontha melolontha.\nC_LIO_LIOur results reveal that the different plant species rely on distinct sets of defense strategies. The spotted knapweed (Centaurea stoebe) resists attack by dissuading the larvae through the release of repellent chemicals. White clover (Trifolium repens) does not repel the herbivore, but reduces feeding, most likely through structural defenses and low nutritional quality. Finally, the common dandelion (Taraxacum officinale) allows M. melolontha to feed abundantly but compensates for tissue loss through induced regrowth.\nC_LIO_LISynthesis: Three co-occurring plant species have evolved different solutions to defend themselves against attack by a generalist root herbivore. The different root defense strategies may reflect distinct defense syndromes.\nC_LI

ecology↗