Recent Development of Biological Control by Beneficial Nematodes: Synopsis and Discussion

The use of nematodes as biological control agents of insects has evolved significantly since this pioneering concept was first employed by Rudolf GLASER in the early 1930s. GLASER and his colleagues (see 4) demonstrated that the entomopathogenic nematode, Steinernema glaseri (Rhabditida: Steinernematidae) could be mass produced and used as an inoculative biological control agent of the Japanese beetle, Popillia japonica. Although other Steinernema species were described after the discovery of S. glaseri, it was the independent finding of S. carpocapsae by DUTKY & HOUGH (2) and WEISER (9) that stimulated further efforts in biological control by beneficial nematodes. Of equal significance was the finding that there is a mutualistic bacterial relationship with these steinernematid nematodes (i.e., Xenorhabdus spp.) (see 3) . Since finding this nematode species, S. carpocapsae and its mutualistic bacterium, X. nematophilus, were used in a number of experiments to control various insect species (see 8) . In the 1970s, other nematodes would contribute to the biological control efforts because insect resistance and environmental and public health problems from the use of chemical insecticides led to an increasing demand for alternatives to insect control. Beneficial insect-parasitic nematodes may offer one of these alternatives. These would include the entomopathogenic nematodes in the genus Heterorhabditis (Rhabditida: Heterorhabditidae) and their mutualistic bacteria, Photorhabdus spp., both of which have a similar mode of infection as Steinernema (see 3) , the mermithid, Romanomermis culicivorax (Stichosomida: Mermithidae) (7) and the tylenchid, Deladenus siricidicola (Tylenchida: Phaenopsitylenchidae) (see 1). Several international forums resulting in published reports on the topic of beneficial nematodes for biological control have been held [e.g., Asilomar, California (3) and Beijing, China (1) 1. COST (Committee on Scientific Technology) , a European organization, has held a number of scientific meetings to discuss and consider many biological facets of entomopathogenic nematodes. Because entomopathogenic nematodes are of commercial interest and can be used as biological insecticides, these international forums have understandably focused on them. In addition, ISHIBASHI (5, 6) has summarized much of the research efforts of Japanese scientists. In this Tsukuba Symposium sponsored by the Japanese Nematological Society, the emphasis has focused on the recent developments by leading scientists working in the field of biological control by beneficial nematodes, particularly on the entomopathogenic ones. We report herein a synopsis of the major points made by the speakers and of the discussion that followed the presentations.