PATHOGENICITY OF NEW COMBINATIONS OF HETERORHABDITIS SPP. AND PHOTORHABDUS-LUMINESCENS AGAINST GALLERIA-MELLONELLA AND TIPULA-OLERACEA

Photorhabdus luminescens isolates were exchanged between four entomopa thogenic nematode strains; two isolates of Heterorhabditis megidis fro m The Netherlands and two isolates of H. bacteriophora, one from Austr alia and one from Moldavia. When cultured on H. megidis symbionts only few H. bacteriophora infective juveniles retained the symbiotic bacte rium. These infective juveniles, without symbiotic bacteria, were not pathogenic to insects. When P. luminescens was injected into insect la rvae it could kill Galleria mellonella (Lepidoptera: Galleridae) larva e but it was not pathogenic to Tipula oleracea (Diptera: Tipulidae). T he combination of nematode and bacterium killed T. oleracea, showing t hat the nematode is more than just a vector for the bacterium. Small d ifferences in pathogenicity between the combinations could only be obs erved in T. oleracea, not in the highly susceptible G. mellonella. The pathogenicity of a combination depends on the pathogenicity of the ba cterium, the pathogenicity of the nematode and the interaction between them. The pathogenicity of H. bacteriophora strains against T. olerac ea was low, partly because of the low penetration rate of these strain s. (C) 1998 Academic Press.