The susceptibility of tsetse flies (Diptera: Glossinidae), Glossina palpalis gambiensis (Vanderplank), and G. m. morsitans (Westwood) to topically applied spinosad, a mixture of insecticidal molecules from the actinomycete Saccharopolyspora spinosa, is almost as high as to deltamethrin. However, susceptibility to spinosad does not differ significantly between teneral and gravid flies, contrary to deltamethrin. Spinosad might be a promising candidate for future tsetse control by the sequential aerial technique.