Flooding impacts on soybean aphid virulence dynamics: Implications for insect resistance management under a changing climate

Abiotic stressors associated with global climate change disrupt insect – plant interactions in myriad ways. In agricultural systems, abiotic stress may threaten the long-term adoption of insect resistant crops (i.e. host plant resistance; HPR) as a sustainable management tactic. Indeed, abiotic stress in plants induces a complex cascade of physiological changes that can alter plant susceptibility to insect herbivores. These changes can directly impact insect population growth rates, although the longer-term evolutionary consequences remain unclear, including the extent to which abiotic stress could favor insect adaptions to overcome HPR (i.e. virulence). We used soybeans (Glycine max) and the invasive, pestiferous soybean aphid (Aphis glycines) as a model system to address this knowledge gap, conducting greenhouse and laboratory experiments to compare how one abiotic stressor, flooding, differentially affects virulent and avirulent soybean aphid biotypes. We quantified changes in soybean phytohormone content under different combinations of aphid infestation and flood stress as a marker for soybean defensive trait expression. To correlate these data with direct impacts on aphid fitness, we also conducted life table analyses and performed RNA sequencing to measure changes in aphid gene expression under periods of host plant flood stress. Overall, virulent aphids exhibited a muted transcriptomic and phenotypic response to flooding relative to their avirulent conspecifics. Our results indicate that virulent soybean aphids may be more resilient to flooding, introducing a fitness differential that could facilitate the spread of virulence adaptations as climate change effects intensity. Long-term, understanding these interactions will be critical for preserving HPR crops.