Differentiating between scavengers and entomopathogenic nematodes: Which is Oscheius chongmingensis?

Entomopathogenic nematodes (EPNs) continue to be explored for their potential usefulness in biological control and pest management programs. As more insect-associated species of nematodes are discovered and described, it is possible that scavengers and kleptoparasites may be mischaracterized as EPNs. If a nematode species is truly an entomopathogen it should display similar infectivity, as well as behaviors and preferences, to those of established EPN species, such as Steinernema carpocapsae. In this study we evaluated dauers of the putative EPN species Oscheius chongmingensis. We examined virulence, odor preferences as a measure of host-seeking behavior, and features of its bacterial symbiont Serratia nematodiphila. We determined that O. chongmingensis behaves more like a scavenger than an EPN. Not only did O. chongmingensis exhibit very poor pathogenicity in Galleria mellonella (wax moth larvae), it also displayed odor (host-seeking) preferences that are contrary to the well-known EPN S. carpocapsae. We also found that the bacterial symbiont of O. chongmingensis was antagonistic to S. carpocapsae; S. carpocapsae IJs were unable to develop when S. nematodiphila was a primary food source. We conclude that there is insufficient evidence to support the characterization of O. chongmingensis as an EPN; and based on the attributes of its preferences for already-infected or deceased hosts, suggest that this nematode is a scavenger, which may be on an evolutionary trajectory leading to an entomopathogenic lifestyle.