The cost of fighting for surviving in a complex world: entomopathogenic nematodes as scavengers

Resumen del trabajo presentado en el International Congress on Invertebrate Pathology and Microbial Control - 53rd Annual Meeting of the Society for Invertebrate Pathology, celebrado de forma virtual del 28 de junio al 2 de julio de 2021Entomopathogenic nematodes (EPNs) in the traditional families Steinernematidae and Heterorhabditidae are relevant and well-studied agents for the biological control of soil crop insect pests. Theoretically, their infective juvenile (IJ) stages existing in soils can act as entomopathogens colonizing live hosts or as facultative scavengers reproducing within dead hosts. Whether both paths are equally successful for EPNs is still poorly understood. Several studies proved that EPNs complete their life-cycle within freeze-killed hosts whose reproductive success depends on the host species, the number of IJs, and the presence of other scavengers, including free-living nematode (FLN) species in the genera Oscheius, Acrobeloides, and Pristionchus. In any case, the EPN offspring is commonly lower for IJs that reproduced as scavengers. Laboratory experiments also showed that high competitive pressures of FLNs reduced the virulence of IJs that emerged in low numbers from freeze-killed larvae. Alike, mix EPN and FLN progenies derived from infected larvae in soil baits often compromised EPN reproductive success. Some FLNs can even appear in nematode progenies of Koch's postulates tests. Whether this fact is due to FLNs behaving as entomopathogens or to the unnoticed presence of steinernematids or heterorhabditids are possibilities to consider for FLN species not included in the traditional EPN families. Further studies involving different soil-dwelling organisms, including the EPN symbiont bacteria, will be required to unravel the complex interactions occurring in soils and the diverse roles that each of them could play to increase their chances of success