RESPONSE OF INFECTIVE STAGE PARASITES (NEMATODA, STEINERNEMATIDAE) TOVOLATILE CUES FROM INFECTED HOSTS

Volatile infochemicals play a significant role in the interactions bet ween trophic levels. Volatile infochemicals may allow species within t he third trophic level to avoid patches where conspecifics or heterosp ecifics are present. We show odor-mediated resource assessment by ento mopathogenic nematodes in the family Steinernematidae. We hypothesized that the infective juvenile nematodes may reduce inter- and intraspec ific competition by responding differently to unparasitized hosts vs. hosts parasitized by conspecific or heterospecific nematodes. All Stei nernema spp. except S. carpocapsae were attracted to hosts that were n ot parasitized. Steinernema carpocapsae infective juveniles were repel led from hosts infected for 4 hr with all heterospecific infections ex cept S. anomali, whereas S. glaseri were repelled only from S. riobrav is-infected hosts. Steinernema feltiae did not differentiate any heter ospecific or heterogeneric infections. Steinernema glaseri were attrac ted to four of five heterospecific infections and S. anomali and S. ri obravis were attracted to two of five heterospecific infections. Both S. anomali and S. glaseri were more attracted to hosts infected with t he out-group Heterorhabditis bacteriophora than those infected by cons pecific nematodes. Infective juvenile S. carpocapsae, S. anomali, and S. glaseri were more attracted to insects colonized by conspecific nem atodes than to uninfested insects. Infective juvenile S. carpocapsae w ere repelled from the 24-hr-old conspecific infections, whereas S. gla seri were less attracted to 24- than to 4-hr-old conspecific infection s. Experiments with insects injected with bacteria from the nematodes suggested the latter as the source of active volatiles. We suggest tha t odor-mediated host recognition by infective juveniles may reduce int er- and intraspecific competition among Steinemematidae.