Molecular mechanisms of pesticide selectivity: Insights from acaricide toxicology

Broad-spectrum pesticides have been used for decades to control a wide range of crop pests and vectors of human and animal diseases. However, concerns about the environment and human health have provided a strong impetus to design more selective molecules that can be safely used in integrated pest management (IPM) programs. In addition, selectivity is crucial for the direct use of compounds on humans and animals, with in-hive use of acaricides for treatment of Varroa on bees as an extreme example. Pesticide selectivity is mainly achieved via physiological or ecological factors. The mechanisms underlying physiological selectivity can be based on either differential penetration, excretion or metabolism, differences in affinity of the target-site proteins, or a combination of both. Metabolism-based selectivity can be achieved both through species-specific activation, as well as detoxification. Many acaricides, compounds that specifically target mite and tick species, are highly selective with little efficacy on insects. This selectivity has been documented for historical reference acaricides that have been used for several decades, but also for more recently developed chemicals. Molecular insights into the mechanisms of selectivity are crucial in devising new compounds that specifically target certain pests. In this review, we provide an overview of what is known about the molecular mechanisms of acaricide selectivity.