Four factorial experiments were conducted in which groups ofReticulitermes flavipesworkers containing up to 13.3% of a second caste (soldiers, short-wing-pad nymphs, long-wing-pad nymphs, or female neotenics) were exposed to various concentrations of the insect growth regulator methoprene. For all experiments the main effect of the factor “methoprene concentration” dominated the results. Large numbers of presoldiers were produced, as well as a loss of hindgut protozoan symbionts. In the two experiments with long-wing-pad nymphs and female neotenics, the factor “initial caste proportion” was also significant, but was complicated by a statistically significant “methoprene concentration”—“caste proportion” interaction. These effects were relatively minor, however, compared with the main effect of methoprene concentration and suggest that the presence of nonworker castes in their normal proportions do not militate the disruptive effects of exogenous juvenile hormone analogs.