Entomopathogenic nematodes (EPNs) are organisms that can be used in biological control programs for plant protection. In order to optimize their use we studied chemotropism of infective juveniles (IJs) of EPNs Steinernema feltiae, S. carpocapsae, S. kraussei and Heterorhabditis bacteriophora to volatile compounds (VOCs). The study included 6 VOCs secreted by Brassica nigra L. roots; dimethyl sulfide [DMS], dimethyl disulfide [DMDS], dimethyl trisulfide [DMTS], allyl isothiocyanate [AITC], phenylethyl isothiocyanate [PITC], and benzonitrile [BN]). Damage of B. nigra roots was caused by cabbage fly (Delia radicum [L.]) larvae. We hypothesized that attraction behavior exhibited by the EPNs toward the tested VOCs could be related to the species and would vary with foraging strategy, VOC, time of exposure and temperature. The chemotaxis assay was performed under laboratory conditions in Petri dishes, which contained agar. Experiment was conducted at two studied temperatures (20 and 25 °C) and 75 % relative humidity. The movement of IJs was observed after 4 and 24 hrs. Based on our results we calculated chemotaxis index with aim to determine if VOC is attractant, repellent or has no effect on EPNs. Results of our investigation showed that S. 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. Movement of other EPNs species was less prominent. The movement of different EPN species towards VOCs was influenced by temperature. At higher temperature (25 °C) the movement was more prominent. The chemotaxis index values showed, that all of the VOCs tested in our assay repelled S. kraussei at both experimental temperatures, suggesting that sulfur compounds (sulfides) and glucosinolate breakdown products (isothiocyanate and benzonitrile) could play an important role in EPNs navigation and in indirect defense of plants against pests.
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