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

Effects of two acaricides, permethrin and amitraz, with different modes of action, on gas exchange and water balance 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 with acetone (a solvent) 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 a similar initial major water loss, as in permethrin-treated ticks, followed by a second period of water loss activity at 10–14 h 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 μl h⁻¹) was similar to that of the untreated ticks (0.461 μl h⁻¹). Compared to untreated control ticks, permethrin-, amitraz-, and the acaricide mixture-treated ticks exhibited significantly increased SMR (1.054, 1.392 and 1.520 μl h⁻¹ 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. In addition, the study may provide insight into the modes of action of these two acaricides in tick physiology. The results may also help understand the mechanism of synergism between permethrin and amitraz that was reported previously in other ticks and insects.