The double trouble of insect attacks and water stress: using natural variation in plant adaptations to a water gradient to elucidate how plants defend against insect herbivory when facing water stress

As predicted by global climate change models, an increasing challenge in agriculture is to cope with more severe outbreaks of insects against the backdrop of more frequent drought and heavy rain events. The problem is magnified since an excess as well as a shortage of water not only reduces yield but may also reduce crop resistance to insect herbivores. Although plants in nature and agriculture commonly face combinations of biotic and abiotic stresses, responses to these stresses have usually been studied separately. To breed resilient crops, it is critical to understand how plants deal with a combination of biotic and abiotic stress. I will use natural variation in water stress adaptations in the plant genus Rorippa to elucidate how plants integrate abiotic stress by excess or shortage of water with biotic stress by insect herbivores. Using a multidisciplinary approach involving insect behavioral ecology, plant transcriptomic, and metabolomics, I will elucidate: I) how closely related plant species that grow along a water gradient are adapted to defend themselves against herbivores of different feeding guilds when subjected to different types of water stress, II) how well these plant species are able to recruit natural enemies of the herbivores, and III) unravel the underlying mechanism by which plants integrate responses to water stress and herbivory. In a world with increasing weather extremes, this knowledge will aid plant breeders in the development of new crop varieties that can cope with combined stress and grow on marginal lands, leading to increased agricultural productivity and resilience.