An exotic entomopathogenic nematode (EPN), Steinernema riobrave, was applied beneath trees in a Florida citrus orchard to control soilborne larvae of Diaprepes abbreviatus. Within two weeks, in treated compared to untreated plots, there were significant increases in mortality of sentinel weevil larvae, prevalence of the nematophagous fungi Arthrobotrys sp. and Dactylaria sp., and prevalence of free-living bactivorous nematodes in cadavers of sentinel weevils. Six weeks following treatment, fewer sentinel weevil larvae died in treated compared to untreated plots. Application of composted manure beneath trees decreased the prevalence of nematophagous fungi, increased the prevalence of endemic EPN, and increased the mortality of sentinel weevil larvae. In the laboratory, addition of S. riobrave to orchard soil increased mortality of S. riobrave and an endemic EPN, S. diaprepesi, added to the soil five days later. The effect did not occur in soil air-dried to disrupt fungal activity prior to the experiment. Survival of the endemic EPN, Heterorhabditis zealandica, was unaffected by pretreatment with S. riobrave in raw or air-dried soil. Prevalence of the nematophagous fungi Catenaria sp., Arthrobotrys sp., and Dactylaria sp. was increased by application to soil of S. riobrave and S. diaprepesi, but not by application of H. zealandica. Results support the hypothesis that EPN augmentation adversely affects the endemic EPN community by increasing numbers of density-dependent nematodes antagonists. Experiments also demonstrated that augmenting endemic EPN community with appropriate EPN species and use of some types of mulches may mitigate non-target effects.