Synergism of Adulticides and Insect Growth Regulators Against Larval Cat Fleas (Siphonaptera: Pulicidae).

The use of topical and oral therapies on pets has revolutionized the control of cat fleas, Ctenocephalides felis felis (Bouché). Herein, we tested the biological activity of two adulticides, fipronil and imidacloprid, and the insect growth regulators (IGRs), methoprene and pyriproxyfen. The LC50's of fipronil, imidacloprid, methoprene, and pyriproxyfen in larval rearing medium for second and third instars were 1.13, 0.73, 0.35, and 0.23 ppm, respectively. Combinations of imidacloprid and methoprene and pyriproxyfen were synergistic. The combination indices (CIs) at an effective dose (ED95) of imidacloprid:methoprene (Im:Meth) were 0.54, 0.44, 0.66, 0.73, and 0.62 for Im1:Meth1, Im5:Meth1, Im10:Meth1, Im20:Meth1, and Im40:Meth1, respectively. Similarly, the CIs of imidacloprid:pyriproxyfen (Im:Pyri) at an ED95 were 0.73 and 0.50 for Im1:Pyri1 and Im5:Pyri1, respectively. Combinations of fipronil:methoprene (Fip:Meth) provided variable results with Fip1:Meth1 being antagonistic (CI = 1.61). Combinations at 5:1, 10:1, and 20:1 at an ED95 were moderately synergistic. Combinations of Fip:Pyri at 1:1 were antagonistic at an ED95 with a CI of 2.87. When the combinations were reversed, neither the imidacloprid nor fipronil synergized either IGR. The dose response indices (DRI) for both Im:Meth and Im:Pyri indicate that the concentrations of the combinations could be significantly reduced and still be as effective as imidacloprid alone. Certain combinations of adulticides and IGRs were synergistic against immature fleas.

Intrinsic Activity of IGRs Against Larval Cat Fleas.

Insect growth regulators (IGRs) such as lufenuron, methoprene, and pyriproxyfen have been important tools in the integrated pest management of cat fleas, Ctenocephalides felis (Bouché), for the past two decades. Other IGRs have been registered for the control of termite, dipteran, and lepidopterous pests including chlorfluazuron, cyromazine, dicyclanil, and precocene I, but have been not tested against C. felis. The intrinsic activity of IGRs was determined by exposing larvae to treated larval rearing media. The LC50s of chlorfluazuron, cyromazine, dicyclanil, lufenuron, and precocene I against cat fleas were 0.19, 2.66, 0.04, 0.20, and 10.97 ppm, respectively. The LC95s of chlorfluazuron, cyromazine, dicyclanil, lufenuron, and precocene I were 0.78, 51.24, 0.30, 0.62, and 175.05, respectively. The regression slopes of chlorfluazuron and lufenuron were 2.65 ± 0.24 and 3.40 ± 0.45 (SEM), respectively, and considerably steeper than the other IGRs tested (1.51 to 1.74). The intrinsic activity of IGRs tested is summarized as dicyclanil > chlorfluazuron = lufenuron > cyromazine > precocene I. The responses of the laboratory UCR strain to these IGRs can serve as a baseline of susceptibility until a more susceptible cat flea strain is found. Chlorfluazuron and dicyclanil look like promising candidates against cat fleas.