Behavioural responses of an entomopathogenic nematode (Steinernema carpocapsae) to an insect semiochemical and...

Many parasitic nematodes exhibit a range of behavioural responses to host-associated stimuli, especially chemicals. The infective juveniles (IJs) of specialized insect-infecting nematodes, i.e., entomopathogenic nematodes (EPNs), can show directed movement (taxis) or other behaviours in response to odorants. However, relatively little is known in terms of IJ responses in the context of increases in non-directed movement (kinesis) resulting from physical contact with host chemicals, or the effects of insect semiochemicals on EPN behaviours. We individually exposed IJs of the EPN Steinernema carpocapsae to solutions representing five different treatments, including those containing the macerated tissues of a suitable insect host (greater wax moth larvae - waxworms) or a semiochemical (1-pentadecene) secreted by various insects. We conducted behavioural observations at six time points over an 8-h period, measuring the total number of movements by each IJ (orthokinesis), along with the occurrence of side-to-side movements (klinokinesis) or head-waving. We found that IJs in the waxworm or 1-pentadecene solutions showed high levels of overall movement, but waxworm-exposed IJs also exhibited the most sinusoidal movement, whereas IJs exposed to 1-pentadecene exhibited far more head-waving than nematodes in the other treatments. These results indicate that S. carpocapsae shows behavioural responses through kinesis when exposed to host chemical cues in an aqueous medium. As our study is only the second report of EPNs responding to an insect semiochemical, this is a promising area for future studies to better understand host-finding strategies by these nematodes, with possible applications for their use in insect biocontrol.