Unravelling interactions between entomopathogenic and plant-parasitic nematodes: insights from two-choice experiments

Root-knot nematodes (RKNs) cause major yield losses in horticultural systems worldwide. With increasing restrictions on chemical nematicides, environmentally sustainable alternatives such as entomopathogenic nematodes (EPNs) and derivatives of their symbiotic bacteria are gaining attention. However, it remains unclear how EPNs and their bacterial products might influence RKN behavior. This study investigated the behavioral responses of the RKN Meloidogyne incognita to EPN-derived treatments, testing the hypothesis that these cues induce directional avoidance when RKNs are given a choice, and that such responses may be modulated by plant presence. Experiments were conducted using two-choice horizontal tube systems filled with moistened sand with and without tomato seedlings ( Solanum lycopersicum cv. Moneymaker). Three EPN Steinernema species were assessed: S. feltiae , S. carpocapsae , and S. riojaense . Treatments included (i) EPN infective juveniles (IJs), (ii) EPN-infected Galleria mellonella cadavers, and (iii) bacterial cell-free supernatant (CFS) derived from Xenorhabdus spp. After inoculation of 1500 M. incognita second-stage juveniles (J2s) into the central tube section, nematode movement was quantified after seven days. Although overall J2 mobility was generally low, with most individuals remaining near the inoculation point, clear patterns still emerged: J2 showed a significant avoidance of EPNs and their derivatives, with the strongest responses observed for cadaver and CFS treatments. Plant presence did not markedly change J2 behavioral patterns; repellency occurred regardless of plant cues, although the presence of plants slightly amplified the effect. These findings advance our understanding of how EPNs and by-products influence RKN behavior, revealing early behavioral barriers that may shape rhizosphere interactions.