The resistant soybean,Glycine max(L.), genotype PI 227687, and the susceptible cultivar ‘Davis’ were evaluated for their effects on development ofCopidosoma truncatellum(Dalman) and its host,Pseudoplusia includens(Walker). Parasitized and nonparasitized larvae were fed either ‘Davis’ (susceptible cultivar) or PI 227687 (resistant genotype). ParasitizedP. includensfed ‘Davis’ consumed 40.7% more leaf area than nonparasitized larvae fed ‘Davis’. ParasitizedP. includenslarvae fed PI 227687 consumed 46.4% more leaf area than nonparasitized larvae on the resistant genotype. Feeding period of parasitized larvalP. includenswas 2 days longer than that of nonparasitized larvae. One-day-old pupal weights of nonparasitizedP. includensfed PI 227687 were significantly lower than for those fed ‘Davis’. ParasitizedP. includensfed ‘Davis’ had significantly greater 1-day-old mummy weights than those fed PI 227687. There was no significant difference in number of parasitoids emerging from host mummies between treatments. Pupation period ofC. truncatellumwas significantly longer for parasitoids that developed inP. includensfed PI 227687 than for those from larvae fed ‘Davis’. There was no significant difference in time required for pupation ofP. includenson either host plant. Overall mortality of nonparasitizedP. includensfed ‘Davis’ was 10%, and nonparasitizedP. includensfed PI 227687 had an overall mortality of 70%. ParasitizedP. includensfed both soybean genotypes experienced 100% mortality. Even though the number of parasitoids able to develop per host is not significantly altered, the high mortality of host larvae before pupation ofC. truncatellummay adversely affect population levels of this parasitoid in fields of resistant soybean.