Oscheius myriophilus: isolation and characterization of new populations from western Lombardy, Italy.

Nematodes are known for their interaction with insects. This interaction ranges from phoretic to facultative and obligatory association. Great attention and research effort was devoted, in the past three decades, to entomopathogenic nematodes from the families Steinernematidae and Heterorhabditidae. In the past decade, there is accumulating evidence that free-living bacterivorous nematodes (FLNs), belonging to the genus Oscheius act as scavengers to compete with EPN for their cadavers. Members of this genus were identified in many locations in the world, Oscheius species are efficiently associated with Serratia bacteria. However, their independent entomo-pathogenicity is still in question. In a recent survey in Lombardy region, Italy we isolated populations of Oscheius which. was then identified, using morphological measurements and molecular tools as Oscheius myriophilus. In a serious of bioassays, the infectivity, and the ability of the various populations to tolerate environmental conditions (heat and desiccation) were assessed. While high infectivity was displayed by the IJs of S. carpocapsae as well as with H. bacteriophora, large variation was observed in the infectivity of the newly O. miryophilus isolates towards Galleria mellonella (L.) (Lepidoptera, Pyralidae) larvae. The mortality of the moth larvae did not correspond directly with the increasing concentrations of the nematodes. Similarly, inconsistent results were obtained in the stress bioassays, displaying large variation among the populations, indicating potential genetic variability among the isolated strains that has to be further explored. Furthers studies are needed to explore their potential as entomopathogens.