EFFECTS OF INFECTED INSECTS ON SECONDARY INVASION OF STEINERNEMATID ENTOMOPATHOGENIC NEMATODES

Factors affecting 'invasion efficiency' of steinernematid entomopathog enic nematodes into hosts were elucidated. The phenomenon that only pa rt (10-40%) of the nematode population invades the target host has bee n recorded in many studies. It has been mainly ascribed to differences in the ability of individual nematodes to infect. In the present stud y the effect of an infected host, the wax moth Galleria mellonella, on subsequent infection of the entomopathogenic nematodes Steinernema ca rpocapsae Mexican, S. riobravus and S. feltiae was evaluated. The inva sion rate of the 3 nematode species to a non-infected host was reduced by 40-60% after pre-exposure to infected hosts. These nematodes regai ned their full invasion potential after they were rinsed with water. I nvasion into insects which were previously injected with nematodes was significantly reduced by 60-80% 6-9 h after injection. The reduction in subsequent invasion due to the initial infection was nematode speci es specific. This phenomenon was also observed with other lepidopteran pests (Helicoverpa armigera and Spodoptera littoralis). The data indi cate that the initial infection by entomopathogenic nematodes induced the release of a substance which reduced the subsequent invasion. The chemical and biological characteristics of this substance are currentl y under investigation.