Infective juveniles ofSteinernema carpocapsaeWeiser andSteinernema scapterisciNguyen&Smart infected nymphal grasshoppers under petri dish and simulated field conditions.S. carpocapsaecaused higher mortality and was more infective (number of nematodes gaining entry to host) thanS. scapterisci. Rate of mortality did not vary significantly among the nymphal instars, but nematodes were more infective in larger nymphs. For hatching grasshoppers digging to the soil surface, mortality and infectivity were positively correlated with soil moisture levels. Pathogenicity was especially enhanced by high humidity at the soil surface. Three sandy soils were also evaluated for effect on mortality and infectivity, but the influence of soil type, while significant, was small relative to soil moisture.