ECOLOGY IN THE SERVICE OF BIOLOGICAL-CONTROL - THE CASE OF ENTOMOPATHOGENIC NEMATODES

Biological control manipulations of natural enemies to reduce pest pop ulations represent large-scale ecological experiments that have both b enefited from and contributed to various areas of modern ecology. Unfo rtunately, economic expediency and the need for rapid implementation o ften require that biological control programs be based more on trial a nd error than on sound ecological theory and testing. This approach ha s led to some remarkable successes but it has also produced dismal fai lures. This point is particularly well illustrated in the historical d evelopment and use of entomopathogenic nematodes for the biological co ntrol of insect pests. Intense effort has focused on developing these natural enemies as alternatives to chemical insecticides, in part beca use laboratory assays indicated that these nematodes possess a broad h ost range. This illusory attribute launched hundreds of field releases , many of which failed due to ecological barriers to infection that ar e not apparent from laboratory exposures, where conditions are optimal and host-parasite contact assured. For example, the entomopathogenic nematode Steinernema carpocapsae is a poor choice to control scarab la rvae because this nematode uses an ambusher foraging strategy near the soil surface whereas the equally sedentary scarab remains within the soil profile, shows a weak host recognition response to scarabs, has d ifficulty overcoming the scarab immune response, and has low reproduct ion in this host. Conversely, two other nematodes, Heterorhabditis bac teriophora and S. glaseri, are highly adapted to parasitize scarabs: t hey use a cruising foraging strategy, respond strongly to scarabs, eas ily overcome the immune response, and reproduce well in these hosts. I ncreased understanding of the ecology of entomopathogenic nematodes ha s enabled better matches between parasites and hosts, and more accurat e predictions of field performance. These results underline the import ance of a strong partnership between basic and applied ecology in the area of biological control.