Emergence and Dispersal Patterns of Two Isolates of the Entomopathogenic Nematode <I>Steinernema feltiae</I>


  • A. N. Rolston
  • C. T. Griffin
  • M. J. Downes


dispersal, infective juvenile, male colonisation, nematode, sex ratio.


Few studies have addressed the role of the sexes in the emergence and dispersal of entomopathogenic nematodes from host insects. Individuals of two isolates of Steinernema feltiae, UK76 and SBI1, emerging from Galleria mellonella cadavers were classed as Non-Dispersed (remaining on the cadaver for up to nine days) and Dispersed (actively moving away from the cadaver). Sex ratios within both classes were examined in infective (individuals that successfully invaded bait G. mellonella) and entire (infective and noninfective individuals that matured in hanging drops of G. mellonella haemolymph) populations. Sex ratios differed significantly from 1:1 only in the SBI1 Non-Dispersed entire population (female bias) and SBI1 Non-Dispersed infective population (male bias). For each isolate, Dispersed individuals were significantly more infective than Non-Dispersed. However, only 11% of SBI1 and 22% of UK76 Non-Dispersed individuals were found to be mature infective juveniles (IJ) compared with 78% of SBI1 and 82% of UK76 Dispersed individuals (based on survival in SDS). Infective juveniles dispersing towards distant radial bait G. mellonella tended to migrate from the head region of the natal cadaver. For each isolate, a higher proportion of males than females arrived early at distant baits. SBI1 males survived alone in G. mellonella cadavers for longer periods than did females, which supports the "male colonization" hypothesis.