Response of Infective Stage Parasites (Nematoda: Steinernematidae) to Volatile Cues from Infected Hosts

Volatile infochemicals play a significant role in the interactions between trophic levels. Volatile infochemicals may allow species within the third trophic level to avoid patches where conspecifics or heterospecifics are present. We show odor-mediated resource assessment by entomopathogenic nematodes in the family Steinernematidae. We hypothesized that the infective juvenile nematodes may reduce inter- and intraspecific competition by responding differently to unparasitized hosts vs. hosts parasitized by conspecific or heterospecific nematodes. All Steinernema spp. except S. carpocapsae were attracted to hosts that were not parasitized. Steinernema carpocapsae infective juveniles were repelled from hosts infected for 4 hr with all heterospecific infections except S. anomaliwhereas S. glaseri were repelled only from S. riobravis-infected hosts. Steinernema feltiae did not differentiate any heterospecific or heterogeneric infections. Steinernema glaseri were attracted to four of five heterospecific infections and S. anomali and S. riobravis were attracted to two of five heterospecific infections. Both S. anomali and S. glaseri were more attracted to hosts infected with the out-group Heterorhabditis bacteriophora than those infected by conspecific nematodes. Infective juvenile S. carpocapsae S. anomaliand S. glaseri were more attracted to insects colonized by conspecific nematodes than to uninfested insects. Infective juvenile S. carpocapsae were repelled from the 24-hr-old conspecific infections, whereas S. glaseri were less attracted to 24- than to 4-hr-old conspecific infections. Experiments with insects injected with bacteria from the nematodes suggested the latter as the source of active volatiles. We suggest that odor-mediated host recognition by infective juveniles may reduce inter- and intraspecific competition among Steinernematidae.