Entomopathogenic nematodes avoid the scent of predatory mites

The utility of entomopathogenic nematodes (EPNs) in integrated pest management programs is limited by their poor persistence in soil. Abiotic soil conditions such as temperature, moisture, and texture modulate persistence of EPNs, and top-down regulation by predators and diseases may also drive survival rates. To better understand how EPNs cope with microarthropod predators, we conducted assays to measure chemotactic responses of the EPN, Heterorhabditis bacteriophora, to the mesostigmatid mite, Stratiolaelaps scimitus. Preliminary observations in a sand/organic material substrate showed that mixed life stages of the mites reduced the H. bacteriophora IJs recovered with Baermann funnels by more than 80% within one week. When the nematode IJs were placed in two-choice T-tube assay units filled with washed sand ( >150µ), they moved toward H. bacteriophora and away from either S. scimitus, or S. scimitus combined with H. bacteriophora. Using a 'push–pull' headspace collection system combined with gas chromatography-mass spectrometry (GC-MS), two citral isomers, neral and geranial, were recovered from S. scimitus. Both compounds were repellent to H. bacteriophora in T-tube assays. Research to detect additional EPN semiochemicals that may interact with nematode response to these compounds is ongoing. Our results suggest that EPN have may have evolved the ability to detect and respond to neral and/or its isomers as a kairomone indicating danger (i.e. predation).