Phoretic dispersal of entomopathogenic nematodes by Hylobius abietis

Phoresis is a strategy in which one organism (the phoretic) attaches to another (the host) for the implied purpose of dispersal and is valuable for small flightless invertebrates with limited mobility. Previous work has shown that the relatively immobile larvae of Hylobius abietis (the large pine weevil) are highly susceptible to entomopathogenic nematodes (EPN) and support nematode reproduction whereas adults do not. Here, we demonstrate that the infective juveniles (IJ) of two species of EPN, Heterorhabditis megidis and Steinernema carpocapsae, can use the resistant but highly mobile adults of H. abietis for phoretic dispersal. The ability to use adult H. abietis for phoresis depended on nematode species and habitat (sand vs peat) and there was no evidence of sex-biased dispersal in S. carpocapsae for which the IJ are dioecious. We hypothesise that phoretic dispersal may be a significant mechanism to avoid sibling competition and inbreeding in EPN, which produce tens of thousands of offspring at point sources in a relatively impenetrable habitat.