Large-scale inoculative releases of the entomopathogenic nematode Steinernema glaseri: Assessment 50 years later

Billions of nematodes were released from 1939 to 1942 throughout the state of New Jersey (563 sites) in an effort to colonize the entomopathogenic species Steinernema glaseri for biological control of the Japanese beetle, Popillia japonica. Because of the onset of World War 11 and the postwar development of chlorinated hydrocarbon insecticides, little effort was expended to evaluate the outcome of these introductions. We evaluated this colonization program by collecting soil samples in 1991 from 304 geographically and ecologically diverse sites across New Jersey. The soil samples were assayed for entomopathogenic nematodes using the Galleria bait method. Overall, 66 (21.7%) soil samples were positive for entomopathogenic nematodes: 24 steinernematids and 42 heterorhabditids. The most common species isolated was Heterorhabditis bacteriophora (38 isolates), followed by S. glaseri (14), S. carpocapsae (4), S. feltiae (4), Heterorhabditis spp. (4), and Steinernema spp. (2). S. glaseri was recovered only from the southernmost third of the state. We conclude that the colonization effort initiated more than 50 years ago was unsuccessful. The reasons remain uncertain, but intolerance of S. glaseri to temperate climates is one likely explanation. That is, southern New Jersey appears to represent the northernmost range of this neotropical species. Moreover, early workers were unaware of the nematode's mutualistically associated bacterium, Xenorhabdus poinarii, which plays important roles in killing insect hosts and in nematode reproductive potential. We show that the bacterium is inhibited by antimicrobial compounds used by these workers during mass rearing, so it is probable that only the nematode portion of the nematode-bacterium complex was released.