Mosquito control: A review on the past, present and future strategies

Nearly half a million deaths occur worldwide annually due to mosquito-borne diseases. Mosquito control has become the major strategy in controlling these diseases, especially in the absence of effective vaccines for disease prevention. At the beginning of the last century, mosquito control was mainly done by personal protection methods and larval control by application of petroleum oil and Paris green powder to water bodies. A breakthrough in mosquito control came in the 1940s with the introduction of synthetic neurotoxic insecticides which could suppress mosquito populations rapidly throughout the globe. However, a resurgence of populations with resistance to these insecticides was witnessed within a decade after their introduction. Environmental pollution caused by synthetic insecticides also became a major concern. Novel personal protection methods, community-level operations on source reduction, insect growth regulators and polystyrene beads for larval control, and biological control were introduced as alternatives. Biological control was mainly by larval predators such as fish, dragonfly nymphs, microcrustaceans and Toxorhynchites larvae; bacterial larvicides such as Bti; plant-based mosquitocides; and green-fabricated nanoparticles. However, even today, mosquito control programmes heavily depend on synthetic neurotoxic insecticides applied through insecticide residual spraying (IRS), fogging, larviciding and impregnated bed nets. Increased detoxification and target site insensitivity, developed as major insecticide resistance mechanisms, have been extensively studied in mosquitoes assisting proper management of available insecticides for which not many alternatives are available. Despite all our efforts, an unprecedented global emergence of mosquito-borne diseases is evident demanding novel strategies for mosquito control. The introduction of transgenic strains of mosquitoes to suppress or replace mosquito populations reducing disease transmission has become the latest effort. Population reduction has been achieved via releasing mosquitoes with a dominant lethal gene (RIDL) and by combining the conventional sterile insect technique (SIT) with Wolbachia mediated incompatible insect technique (IIT). Population replacement has been successful via releasing Wolbachia infected mosquitoes that are refractory to pathogen development and transmission. Advancement of gene- and allelic- drive systems will soon allow us to effectively spread refractory genes and insecticide susceptible alleles into mosquito populations overriding normal inheritance.