ARS | Publication request: Effects of permethrin and amitraz on gas exchange and water loss in unfed adult females of Amblyomma americanum (Acari: Ixodidae)

Submitted to: Journal of Pesticide Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 18, 2012
Publication Date: N/A

Interpretive Summary: The control of tick species of veterinary and medical importance, such as the cattle tick and the lone star tick, relies largely on chemical acaricides. Acaricide resistance has become a real problem for tick control, particularly with the cattle tick Rhipicephalus microplus. As part of an effort to develop acaricides with novel modes of action, a collaborative research project was conducted utilizing new research tools to investigate the molecular and physiological mechanisms of pesticide action on ticks. The lone star tick, Amblyomma americanum, was used in this study. Effects of two acaricides, permethrin and amitraz, on gas exchange and water balance of the lone star tick were examined using a flow-through carbon dioxide (CO2) and water vapor analyzer. Unfed adult female ticks exhibited a distinct discontinuous gas exchange pattern (DGEP) with no measurable water loss. Topical treatment of ticks with a lethal dose of permethrin caused major water loss and significantly increased CO2 release. A small water loss spike was observed for each CO2 release. Treatment of ticks with amitraz interrupted tick gas exchange pattern and significantly increased tick metabolism. Treatment of ticks with a mixture of sub-lethal doses of permethrin and amitraz also caused major water loss and chaotic CO2 release activities. Results obtained from this study clearly demonstrated the detrimental effects of permethrin and amitraz on gas exchange and water balance in A. americanum ticks. The data revealed subtle differences between permethrin and amitraz in their effects on tick metabolism, specifically gas exchange and water loss. These results advance our understanding of the modes of action of these two acaricides on tick physiology. These results advance our understanding of the modes of action of these two acaricides on tick physiology. This information also helps in understanding the mechanism of synergism between permethrin and amitraz that was reported previously in ticks and insects.

Technical Abstract: Effects of permethrin and amitraz on metabolism of the lone star tick, Amblyomma americanum, were examined using a flow-through carbon dioxide (CO2) and water vapor analyzer. Untreated adult female ticks exhibited a distinct discontinuous gas exchange pattern (DGEP) with no measurable water loss. Similarly, ticks treated with acetone showed little change in gas exchange and water loss. Topical treatment of ticks with a lethal dose of permethrin caused immediate major water loss and long-lasting high frequency DGEP, with increased amplitude of CO2 release. A small water loss spike was observed for each CO2 release. Treatment of ticks with amitraz abolished the DGEP and elicited a long-lasting continuous gas exchange pattern, indicating significantly increased tick metabolism. No detectable water loss was observed during amitraz-elicited continuous gas exchange. Treatment of ticks with a mixture of sub-lethal doses of permethrin and amitraz caused major water loss initially, as in permethrin-treated ticks, followed by a second period of water loss activity at 10 to 14 hours after treatment. Mixture of the two acaricides caused immediate onset of major chaotic CO2 release activities with a significantly elevated baseline CO2 emission level. The standard metabolism rate (SMR, VCO2) of acetone-treated ticks (0.452 microliter per hour) was similar to that of the untreated ticks (0.461 microliter per hour). Compared to untreated control ticks, permethrin-, amitraz-, and the acaricide mixture-treated ticks exhibited significantly increased SMR (1.054, 1.392 and 1.520 microliter per hour respectively (P < 0.05)). Results obtained from this study clearly demonstrated the detrimental effects of permethrin and amitraz on CO2 gas exchange and water balance in A. americanum ticks. The data also revealed subtle differences between permethrin and amitraz in their effects on tick metabolism, specifically gas exchange and water loss. These results advance our understanding of the modes of action of these two acaricides in tick physiology. These results advance our understanding of the modes of action of these two acaricides on tick physiology. This information also helps in understanding the synergism between permethrin and amitraz that was reported previously in other ticks and insects.