Investigating how chemical cues from entomopathogenic nematodes modulate cotton plant defenses

Entomopathogenic nematodes (EPNs) are obligate parasites of insects that can be used as biological control agents against agricultural pests. Previous work in the solanaceous crops, potato and tomato, indicates entomopathogenic nematodes release chemical cues that enhance systemic plant resistance and reduce insect feeding damage. It remains unknown whether chemical cues from EPNs increase resistance in other plant species and if this could improve agricultural pest management. The goal of this study was to investigate the influence of EPN-produced cues on cotton plant defenses. We predicted that exposing roots of cotton plants to EPNs would systemically induce higher concentrations of defensive metabolites and reduce herbivore damage. We exposed cotton seedlings to EPNs (Steinernema carpocapsae or Heterorhabditis bacteriophora) by applying infective juveniles or EPN-infected insect cadavers near roots, while control plants were not exposed to EPNs, receiving water or freeze-killed insect cadavers. After 48 hours of exposure, we quantified terpene aldehyde concentrations in terminal leaf tissues. We also conducted feeding bioassays to quantify leaf area removed by Spodoptera frugiperda larvae on EPN-exposed and control plants.