Determination of metabolic resistance mechanisms in pyrethroid-resistant and fipronil-tolerant brown dog ticks

Authors: EIDEN, AMANDA - University Of Florida; KAUFMAN, PHIL - University Of Florida; OI, FAITH - University Of Florida; DARK, MICHAEL - University Of Florida; BLOOMQUIST, JEFFREY - University Of Florida; Miller, Robert

Submitted to: Medical and Veterinary Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2017
Publication Date: 6/22/2017
Citation: Eiden, A., Kaufman, P., Oi, F., Dark, M., Bloomquist, J., Miller, R. 2017. Determination of metabolic resistance mechanisms in pyrethroid-resistant and fipronil-tolerant brown dog ticks. Medical and Veterinary Entomology. 31:243-251.

Interpretive Summary: The brown dog tick is a parasite of domesticated dogs worldwide and is commonly found indoors sometimes in large quantities. Options for the management of brown dog ticks are limited. While there are many products on the market only a few contain unique active ingredients. Previous studies have confirmed resistance to two of these active ingredients in ticks collected in Florida and Texas. This study characterized the resistance in 8 strains of resistant ticks using chemicals that block the detoxifying enzymes present in the tick. The most important metabolic detoxification mechanism for the active ingredient, permethrin, was increased esterase activity, followed by increased cytochrome P450 activity. However, none of the enzyme blocking chemicals affected the level of resistance to a different active ingredient fipronil. Based on this work better products can be developed to control resistant ticks. For example, the addition of esterase and cytochrome P450 blocking chemicals to pyrethoid-based products could make these products more effective. Additionally, rapid resistance diagnosis tools can now be developed as it is now known that increased esterase and cytochome P450 activity is correlated with resistance. It is likely a target site mutation will be found for fipronil resistance since none of the metabolic blocking chemicals affected the level of resistance in the ticks tested. Future work will search for this mutation and could lead to rapid PCR-based detection of resistance. The rapid detection of resistance will allow for efficient management of resistant brown dog ticks in the future.

Technical Abstract: Rhipicephalus sanguineus (Latreille) (Ixodida: Ixodidae) is a three-host dog tick found worldwide that is able to complete its’ entire lifecycle indoors. Options for the management of R. sanguineus are limited and its’ control relies largely on only a few acaricidal active ingredients. Previous studies have confirmed permethrin resistance and fipronil tolerance in R. sanguineus populations, commonly conferred by metabolic detoxification or target site mutations. Herein, five strains of permethrin-resistant and three strains of fipronil-tolerant ticks were evaluated for metabolic resistance using synergists to block metabolic enzymes. Synergist studies were completed with triphenyl phosphate (TPP) for esterase inhibition, piperonyl butoxide (PBO) for cytochrome P450 inhibition, and diethyl maleate (DEM) for glutathione-S-transferase inhibition. Additionally, increased esterase activity was confirmed using gel electrophoresis. The most important metabolic detoxification mechanism in permethrin-resistant ticks was increased esterase activity, followed by increased cytochrome P450 activity. The inhibition of metabolic enzymes did not have a marked impact on fipronil-tolerant tick strains.