Pathogenicity of New Combinations ofHeterorhabditisspp. andPhotorhabdus luminescensagainstGalleria mellonellaandTipula oleracea

Photorhabdus luminescensisolates were exchanged between four entomopathogenic nematode strains; two isolates ofHeterorhabditis megidisfrom The Netherlands and two isolates ofH. bacteriophora, one from Australia and one from Moldavia. When cultured onH. megidissymbionts only fewH. bacteriophorainfective juveniles retained the symbiotic bacterium. These infective juveniles, without symbiotic bacteria, were not pathogenic to insects. WhenP. luminescenswas injected into insect larvae it could killGalleria mellonella(Lepidoptera: Galleridae) larvae but it was not pathogenic toTipula oleracea(Diptera: Tipulidae). The combination of nematode and bacterium killedT. oleracea, showing that the nematode is more than just a vector for the bacterium. Small differences in pathogenicity between the combinations could only be observed inT. oleracea, not in the highly susceptibleG. mellonella. The pathogenicity of a combination depends on the pathogenicity of the bacterium, the pathogenicity of the nematode and the interaction between them. The pathogenicity ofH. bacteriophorastrains againstT. oleraceawas low, partly because of the low penetration rate of these strains.