Components of successful pest management programs must be complementary and not antagonistic. This project examined interactions between natural enemies of the black cutworm, Agrotis ipsilon (Hufnagel), an important turfgrass pest, and host plant resistance by endophytic grass. Agrotis ipsilon nucleopolyhedrovirus (AgipMNPV) was examined as a bio-insecticide for controlling A. ipsilon in turfgrass. Fresh (1-week-old) AgipMNPV residues killed 76−86% of neonates hatching from eggs on golf course tees, however, residual control of implanted larvae lasted no more than a few weeks. Combinations of AgipMNPV with adjuvants, such as optical brightener and lignin, failed to accelerate or extend efficacy of the virus. AgipMNPV seems better suited for targeted control of early instars than for season-long control. Several applications per growing season would likely be needed to maintain high enough titers on turfgrass to effectively control cutworms. The addition of a chitin synthesis inhibiting turfgrass fungicide failed to synergize AgipMNPV infectivity to A. ipsilon. Choice tests revealed the fungicide residues to be a mild feeding deterrent, the likely cause of slightly reduced mortality from virus infection seen in field trials. Combination applications in turfgrass might interfere with larval ingestion of a lethal virus dose, resulting in prolonged feeding in the field. I examined how feeding on perennial ryegrass (Lolium perenne) with or without Neotyphodium lolii, its alkaloid-producing fungal endophyte, affects susceptibility of A. ipsilon to AgipMNPV. Feeding on endophytic grass neither compromises nor synergizes infectivity of AgipMNPV in the cutworm midgut. However, reduced consumption or avoidance of less-palatable endophytic grass could decrease ingestion of virus and rates of subsequent mortality in the field. Host feeding on endophytic grass had differing effects on the tachinid fly, Linnaemya comta, a fast-developing solitary parasitoid, and the encyrtid wasp, Copidosoma bakeri, a slow-developing gregarious parasitoid. L. comta development did not appear to be affected when its host fed on endophytic grass; in contrast, C. bakeri suffered negative fitness effects. These results suggest that parasitoid life strategy and taxonomy play a role in endophyte mediated tritrophic interactions.