Attraction behaviors: are synthetic volatiles, typically emitted by insect-damaged Brassica nigra roots, navigation signals for entomopathogenic nematodes (Steinernema and Heterorhabditis)?

We tested the chemotactic response of infective juveniles (IJs) of the entomopathogenic nematodes (EPNs) Steinernema feltiae, S. kraussei, Heterorhabditis bacteriophora, and S. carpocapsae, to the synthetic volatiles (dimethyl sulfide [DMS], dimethyl disulfide [DMDS], dimethyl trisulfide [DMTS], allyl isothiocyanate [AITC], phenylethyl isothiocyanate [PITC], and benzonitrile [BN]) typically emitted by insect-damaged Brassica nigra roots. We hypothesized that attraction behavior exhibited by the EPNs toward the tested volatile compounds (VOCs) could be related to the species and would vary with foraging strategy, VOC, time of exposure and temperature. Steinernema kraussei was the most mobile species in our assay, and at 20 °C, more than 35% of S. kraussei IJs moved to the outer circles of the Petri dishes, while among the other tested EPN species, the greatest movement was observed in H. bacteriophora (10%). The movement of different EPNs species towards VOCs was influenced by temperature. All of the compounds tested in our assay repelled S. kraussei at both experimental temperatures, suggesting that sulfur compounds and glucosinolate breakdown products could play an important role in EPNs navigation.