Genotypic analysis of heterorhabditis isolates from north Carolina.

Different species and strains of pathogens and predators differ in their effectiveness as biological control agents of insects. These differences have been well documented for predatory insects, parasitoids, and a number of entomopathogens (9). The importance of such interspecific and intraspecific variation has been recognized and demonstrated for insect-parasitic steinernematids and heterorhabditids (3). An appreciation of the potential benefits of screening different species and strains of nematode for a particular pest insect on a given crop is necessary in order to optimize the value of collecting and maintaining a large number of nematode isolates from around the world for use as biological control agents. Heterorhabditid nematodes have been collected from insects and soil samples from Australasia, the Americas, and Europe (2,10). Four species have been described: namely, Heterorhabditis heliothidis (Khan, Brooks, and Hirschmann, 1976) Poinar, Thomas, and Hess, 1977; H. bacteriophora Poinar, 1976; H. hoptha (Turco), 1970; and H. hambletoni (Pereira), 1937. Numerous isolates of Heterorhabditis from North Carolina have been tentatively identified on the basis of morphology as H. heliothidis (2). The possibility