The annual bluegrass weevil (Listronotus maculicollis Dietz) (ABW) is a destructive pest of close cut golf course turfgrass in the Northeastern United States. Early instar larvae are stem borers and protected from most treatments, therefore ABW management largely depends on preventive chemicals to suppress egg laying adults. In an effort to develop less toxic ABW management tools, we are investigating the role of natural enemies, namely entomopathogenic nematodes (EPNs), in the population dynamics of ABW. Between 2005 and 2007 we monitored the effect that endemic EPNs have on ABW population dynamics at three golf courses in New Jersey. Two species of EPNs, Heterorhabditis bacteriophora and Steinernema carpocapsae, were detected each year. EPN densities varied dramatically among sites and years yet showed a similar seasonality to their abundance. EPN densities were highest in late June when ABW soil stages were densest, followed by a dramatic decline as temperatures increased and soil moisture and host density decreased. In 2006, the impact of EPNs was shown to be greatest during the 1st generation, yet independent of ABW or EPN densities between sites. Infections were found in all stages between third instar and teneral adult but the majority in 4th and 5th instars. Heavy rainfall in April 2007 lead to significantly lower EPN densities found prior to the peak of 1st generation ABW and consequently fewer infections. All populations exhibited seasonal increases in EPNs and greater generational mortality to the 2nd generation.