HOST RECOGNITION BEHAVIOR BY ENTOMOPATHOGENIC NEMATODES DURING CONTACT WITH INSECT GUT CONTENTS

Host recognition is an important step in the life cycle of most parasi tes. We tested whether host recognition by entomopathogenic nematodes occurs through contact with insect gut contents and whether this recog nition is important to successful infection. Behavioral responses of 4 species of entomopathogenic nematodes, Heterorhabditis bacteriophora, Steinernema carpocapsae, Steinernema glaseri, and Steinernema scapter isci, were studied during contact with the gut contents of insects of 4 species: Acheta domesticus, Blatella germanica, Popillia japonica, a nd Spodoptera exigua. During contact with gut contents of insects of 1 or more species, the nematodes reduced the duration of forward crawli ng and increased the frequency and/or duration of 1 or more search par ameters, including head waving, body waving, backward crawling, stoppi ng, head rubbing, and head thrusting. A significant increase in head t hrusting, presumably a host-penetration behavior, during contact with gut contents of an insect usually was related to successful parasitiza tion. Our results suggest that H. bacteriophora may be more host speci fic than S. glaseri. All nematode species except S. glaseri caused hig her mortality of the insects belonging to the species or orders from w hich the nematodes have been naturally isolated, especially at lower d osage rates. Differences in infectivity of nematodes were related part ially to host recognition behavior. We conclude that nematodes recogni zed gut contents of potential host insects, but this recognition is no t always essential for successful infection.