A modified binomial model that describes the infection dynamics of the entomopathogenic nematode Steinernema feltiae (Steinernematidae; Nematoda)

SUMMARY Third-stage (dauer) juveniles of the entomopathogenic nematode Steinernema feltiae from 3 laboratory populations were tested for infectivity to larvae of the sciarid fly Lycoriellia solani. Bioassay experiments were done to assess the effects of nematode application density, exposure time and host density on the proportion of individuals that established infection. When dauer stages were presented to a host singly, establishment rates of 28, 26 and 18% were obtained for the 3 populations, but the presence of conspecifics consistently increased the rate of establishment to 42, 33 and 21% respectively, at 20 nematodes per host. A modified binomial model was developed to show that nematode establishment was not related to application density in a linear fashion, as initial infection facilitated secondary colonization. The data suggest that 3 subpopulations of nematodes may be distinguished by their infection behaviour: a first group of individuals with the behavioural propensity to initiate infection in unparasitized insects, a second that only invaded infected hosts, and a third group of non-invaders that failed to establish in L. solani.