Synergism of the IGRs methoprene and pyriproxyfen against cat fleas

The IGRs methoprene and pyriproxyfen have played an important role in the controlling cat fleas in both the environment and on the host. The toxicities of methoprene, pyriproxyfen and combinations of both IGRs to cat flea larvae were determined. The LC₅₀ of methoprene and pyriproxyfen was 0.39 and 0.19 ppm, respectively. The LC₅₀’s of combinations of methoprene:pyriproxyfen in ratios of 1:1, 5:1, 10:1, and 20:1 were 0.14, 0.20 0.20, and 0.20 ppm, respectively. The synergism allowed for a reduction in the concentration of methoprene by one-third. The combinations of pyriproxyfen:methoprene greater than 1:1 were not synergistic. Combinations of methoprene:pyriproxyfen may be effective in increasing residual activity and permit lower dosages to applied to pets.