A strain of Neoaplectana carpocapsae Weiser was discovered in larvae of the grape root borer (GRB) Vitacea politiformis (Harris) in 1974. Subsequent study during 1975-79 of subterranean infections of GRB by N. carpocapsae in 2 Concord,Vitus labrusca L., grape vineyards revealed that mortality was low at both vineyards, being 1.5% for larvae and 0.85% for pupae. Laboratory bioassays demonstrated that high levels (10,000) of dauerlarvae were required to insure high infection levels of newly eclosed, 1-year-and 2-year-old GRB larvae. Several experiments in which inundative populations of N. carpocapsae were adequately applied in various ways in the soil around grape vines failed to infect resident GRB larvae. It was concluded that GRB have evolved a degree of tolerance to N. carpocapsae. The potential of utilizing host origin kairomones to enhance parasitism of the GRB by N. carpocapsae is discussed.