Ambush Foraging Entomopathogenic Nematodes Employ ‘Sprinters' for Long-Distance Dispersal in the Absence of Hosts

Abstract

Ambush foragers must employ a long-distance dispersal strategy to maximize reproductive success in the absence of hosts. This hypothesis was tested by comparing lateral dispersal of the ambusher, Steinernema carpocapsae , and the cruiser, Heterorhabditis bacteriophora , nematodes from infected host cadavers in autoclaved, silt-loam soil in large microcosms (0.05-1.5 m(2)) with or without vegetation in the absence of hosts. Dispersal was estimated by taking soil cores (5 × 2 cm in diameter) from the microcosms at different intervals (6-240 hr) and distances (3.8-61 cm) from the infected host cadavers and baiting with Galleria mellonella larvae. The numbers of baited larvae killed and the numbers of infective juveniles (IJs) penetrated in dead baits were counted to compute the percentage of IJs dispersed from the source cadavers, based on the emergence potential and penetration efficiency of the 2 species, and analyzed. Vegetation enhanced dispersal of both species but more so for H. bacteriophora . Although the pattern of dispersal differed spatio-temporally for the 2 species, average population displacement was similar (∼6 cm/day). A majority of the S. carpocapsae population ambushed close to the source cadaver (<3.8 cm), whereas a majority of H. bacteriophora population dispersed between 7-12 cm away from the source cadaver. About 4% of the S. carpocapsae population dispersed faster than the fastest H. bacteriophora , reaching 30-61 cm, compared to only 2% of the H. bacteriophora population dispersing this far. This use of 'sprinters' for long-distance dispersal may represent an adaptive dispersal strategy by the otherwise ambush forager S. carpocapsae in the absence of hosts.