Olfactory cues from entomopathogenic nematodes vary across species with different foraging strategies, triggering different behavioral responses in prey and competitors

Olfactory cues play important roles in predator-prey interactions. Volatile semiochemicals can aid predator foraging and alert prey organisms to the presence of predators. Previous work suggests that predator traits differentially influence prey behavior, however, empirical data on how prey organisms respond to olfactory cues from predator species with different hunting strategies, and how foraging predators react to cues from potential competitors, is lacking. Furthermore, most research in this area has focused on aquatic and aboveground terrestrial systems, while interactions among belowground, soiling-dwelling organisms have received relatively little attention. Here, we assessed how olfactory cues from two species of entomopathogenic nematodes (EPNs), with different foraging strategies, influenced herbivore (cucumber beetle) and natural enemy (EPN) foraging behavior. We predicted these cues could serve as chemical indicators of increased predation risk, prey availability, or competition. Our findings revealed that foraging cucumber beetle larvae avoided volatile cues from Heterorhabditis bacteriophora (active-foraging EPNs), but not Steinernema carpocapsae (ambusher EPNs). In contrast, foraging H. bacteriophora EPNs were attracted to odors produced by the Steinernema carpocapsae species but not conspecific odors. Notably, the two EPN species produced distinct blends of olfactory cues, with only a few semi-conserved compounds across species. These results indicate that belowground insect herbivores respond differently to olfactory cues from different EPN species, with some EPN species avoiding prey detection, presumably to increase their hunting success. Moreover, active-hunting EPNs were attracted to heterospecific olfactory cues, suggesting these cues indicate greater probability of available prey, rather than strong interspecific competition.