Acaricide resistance monitoring and evaluation of natural active ingredients as repellents of medically significant tick species

Acaricide resistance monitoring and repellent efficacy for ticks of public health importance lags behind efforts targeting agricultural and veterinary pests. Additionally, we have a limited understanding of the conditions and timeframe for resistance  emergence of resistance in tick populations with slow life cycles compared to shorter lived pests, like mosquitoes. Collectively, these issues present  major challenges for public health entomologists. We conducted experiments to determine, for the first time, susceptibility status of the blacklegged tick (Ixodes scapularis), the most medically important tick vector in the US. We compared ticks from an area where permethrin-based tick management (4-poster devices) had been deployed for over a decade. Using a larval packet assay, our results demonstrated reduced susceptibility of ticks relative to a laboratory population, but LC-50 resistance ratios were < 2. Resistance metric are not well connected to field efficacy for this species making the results difficult to interpret in the context of operational control. We also do not know how this reduced permethrin susceptibility may impact the efficacy of permethrin as a repellent. In addition, we evaluated several botanical extracts for repellent effects on two additional public health tick vectors, Lonestar tick, Amblyomma americanum, and the newly introduced Asian Longhorned tick, Haemaphysalis longicornis. Our results show promise for botanical repellents, demonstrating the potential of these alternate tools for personal protection and tick-borne disease prevention. However, continued development and implementation of methods and thresholds to assess susceptibility and repellency for ticks will be essential to ensure their utility well into the future.