Reducing Close Encounters with Insect Pests and Vectors: The Past, Present and Future of Insect Repellents.

Insects acting as agricultural pests or disease vectors represent some of the greatest challenges to global health, food security and economics. Diverse technologies to combat insects of economic and medical importance have been and are continually being developed. These include natural and synthetic chemical insecticides and repellents, mass-trapping approaches and, more recently, an increasingly wide range of biological as well as genetic manipulations of insect vectors/pests. The increase in biological resistance and cross-resistance to many insecticides and repellents, the rapid expansion of human populations, as well as escalating climate change have extended or shifted the active periods and habitats of many insect species, creating new hurdles for attempts to defend humans from insects. At the same time, environmental, ecological and socio-political concerns continue to impact the utility of both current interventions as well as newly emerging innovative strategies. The near exponential increase in insect-based threats highlights the importance of basic and translational studies to design and develop novel technologies to combat detrimental insect populations. This review outlines the history of these challenges and describes the evolution of chemical insect control technologies, while highlighting existing and contemporary approaches to develop and deploy chemical repellents to address this threat to human health and agriculture.