Entomopathogenic nematodes employ multiple strategies to avoid the scent of predation

Abstract

Entomopathogenic nematodes (EPNs) are insect parasites widely used for biological control of economically significant soil pests. Their persistence in soil is shaped by abiotic factors such as temperature, moisture, and soil texture, as well as biotic pressures from predators and pathogens. Predation by mites imposes strong selection pressure, driving the evolution of nematode responses to microarthropod predators. We hypothesized that heterorhabditid and steinernematid nematodes reduce encounters with mites by responding to mite-associated chemical cues. We examined the numerical and behavioral responses of four EPN species—Heterorhabditis bacteriophora, H. indica, Steinernema feltiae, and S. diaprepesi—to the predatory mite Stratiolaelaps scimitus. In a sand/organic substrate, predation by mites significantly reduced nematode recovery: S. diaprepesi by 90 % and H. bacteriophora, H. indica, and S. feltiae by about 50 %, highlighting species-specific susceptibility to predation. H. bacteriophora and S. diaprepesi exhibited active predator avoidance behaviors, while S. feltiae remained stationary, potentially minimizing detection by mites. Surprisingly, H. indica was attracted to mites, suggesting a unique ecological role or possible resistance through physical or chemical defenses. Gas chromatography-mass spectrometry identified two isomers of citral—neral and geranial—emitted by S. scimitus, which repelled H. bacteriophora and S. diaprepesi. These findings suggest that EPNs detect and respond to predator-associated odors, demonstrating the role of chemical signaling in soil predator-prey interactions. Understanding these mechanisms may enhance sustainability of biological pest control in agriculture.