Abstract
Chemical cues play important roles in predator–prey interactions. 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 chemical 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 chemical cues from three species of entomopathogenic nematodes (EPNs), each with a different foraging strategy, 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 chemical cues from Heterorhabditis bacteriophora (active-foraging cruiser EPNs), but not Steinernema carpocapsae (ambusher EPNs) or Steinernema riobrave (intermediate-foraging EPNs). In contrast, foraging H. bacteriophora EPNs were attracted to cues produced by the two Steinernema species but not conspecific cues. Notably, the three EPN species produced distinct blends of olfactory cues, with only a few semi-conserved compounds across species. These results indicate that a belowground insect herbivore responds differently to chemical cues from different EPN species, with some EPN species avoiding prey detection. Moreover, the active-hunting EPNs were attracted to heterospecific cues, suggesting these cues indicate a greater probability of available prey, rather than strong interspecific competition.
Highlights
A major goal among ecologists is to better predict the outcomes of trophic interactions and their cascading consequences for community ecology and ecosystem function (Miller et al 2014; Culshaw-Maurer et al 2020; Descombes et al 2020)
Foraging cucumber beetle larvae differentiated between chemical cues from Heterorhabditis bacteriophora-infected and uninfected control cadavers, avoiding the cruiser EPNinfected cadaver cues
Larvae did not differentiate between A. vittatum infected with Steinernema riobrave or control cadavers (GLM T1,8 = -1.136, p = 0.27) or S. riobrave-infected G. mellonella vs. controls (GLM T1,8 = 1.30, p = 0.22)
Summary
A major goal among ecologists is to better predict the outcomes of trophic interactions and their cascading consequences for community ecology and ecosystem function (Miller et al 2014; Culshaw-Maurer et al 2020; Descombes et al 2020). Growing evidence in the study of predator–prey interactions points to environmental (e.g., climate and habitat) and species (e.g., predator and prey) traits as playing key roles in disentangling this complexity (Rosenheim et al 2004; Luttbeg et al 2020; Wirsing et al 2021). Behavioral traits of both predators and prey are of increasing interest, the role these traits play in non-consumptive effects. Predators face foraging challenges as they compete with other predators for prey, without
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