Density-dependent effects on entomopathogenic nematodes (heterorhabditidae and steinernematidae) within an insect host

Density-dependent factors within a host can have an important influence on the population dynamics of parasites. We compared the effects of increasing entomopathogenic nematode Steinernema carpocapsae and Heterorhabditis bacteriophora density within a Galleria mellonella larva. Although the number of invading nematodes increased with increasing dose, percentage penetration declined. This density-dependent penetration was not sufficient to prevent the detrimental effects of overcrowding. Although both S. carpocapsae and H. bacteriophora had optimal survival at a density of approximately 100 nematodes per host, H. Bacteriophora was better able to tolerate higher densities. Fecundity, measured as female size and infective juvenile production, declined at densities above and below 100 nematodes per host. The longest infective juveniles were produced at the lowest nematode densities, indicating a tradeoff between size and number of progeny. Effects of high density appear to result from competition for limited nutrients within the host. Effects of density should be taken into account in the laboratory culture and field release of entomopathogenic nematodes.