Host recognition by entomopathogenic nematodes: Behavioral response to contact with host feces

Host recognition by entomopathogenic nematodes may occur through contact with insects' excretory products, cuticle, or gut contents. We analyzed the behavioral responses of four species of entomopathogenic nematodes during contact with feces of natural or experimental hosts. Host recognition by nematodes was manifested in alterations in the frequency and/or duration of one or more search parameters including forward crawling, headwaving, body-waving, stopping, backward crawling, head-rubbing, and headthrusting. Heterorhabditis bacteriophora and Steinernema glaseri showed behavioral responses to contact with feces of their natural hosts, Spodoptera exigua (Lepidoptera) and Popillia japonica (Coleoptera), and to the experimental hosts, Acheata domesticus (Orthoptera) and Blatella germanica (Blatteria). Steinernema carpocapsae responded only to B. germanica feces, whereas 5. scapterisci did not significantly respond to any of the insect species. During contact with cockroach feces, all nematodes, except S. scapterisci, showed avoidance behavior. We suggest that ammonia present in cockroach feces is inhibitory to nematodes. Specific host recognition by entomopathogenic nematodes may be an important mechanism to maintain host affinities.