Five stages of malathion-resistant Indianmeal moth (IMM),Plodia interpunctella(Hübner), larvae were tested for their susceptibility to a granulosis virus. The virus was applied as a lactose coprecipitate at concentrations of 0 to 250 mg/kg of IMM diet in increments of 25 mg. At a significance level ofP= 0.01, the 1st- and 2nd-instar larvae were highly susceptible; 3rd instars had an intermediate level of susceptibility; 4th and 5th instars demonstrated relatively little susceptibility. First-instar offspring from IMM that survived treatment suffered 100% mortality in virus-contaminated media.