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11 January 2019 Synergism of Adulticides and Insect Growth Regulators Against Larval Cat Fleas (Siphonaptera: Pulicidae)
Michael K. Rust, W. Lance H. Hemsarth
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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.

© The Author(s) 2019. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail:
Michael K. Rust and W. Lance H. Hemsarth "Synergism of Adulticides and Insect Growth Regulators Against Larval Cat Fleas (Siphonaptera: Pulicidae)," Journal of Medical Entomology 56(3), 790-795, (11 January 2019).
Received: 17 September 2018; Accepted: 18 December 2018; Published: 11 January 2019

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combination index
Ctenocephalides felis felis
juvenile hormone analogs
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