Metabolic Resistance Mechanisms Evident in Generations of Anopheles gambiae (Kisumu) Adults Exposed to Sub-lethal Concentrations of Permethrin Insecticide

Abstract

Background: Anopheles gambiae mosquitoes are one of the best-known of the genus Anopheles because of their predominant role in transmitting the most dangerous malaria parasite species (to humans), Plasmodium falciparum. Unfortunately, An. gambiae mosquitoes have grown resistant to the most popular and widely used insecticides, particularly Permethrin, spreading across Africa. The current study sought to determine the lowest Permethrin concentrations that could be a selection pressure for metabolic resistance development in the renowned adult An. gambiae (Kisumu) mosquito population. Methods: Established, insectary-reared, and fully susceptible strains of Kisumu populations were reared, and exposed for mortality assay and Lowest Sub-lethal Concentrations (LSLCs) determination at the adult stage. Various exposure concentrations were achieved by slightly modifying the Centre for Disease Control (CDC) protocol. Adult Kisumu mosquitoes exposed to the same LSLC over generations were compared with unexposed control populations by way of resistance status and correlating levels of esterase, monooxygenase, and Glutathione-S -transferases (GST) metabolic enzymes. Information obtained was analysed using SPSS 16.0 and Analysis of Variance at P=0.05 with the aid of Graph-Pad prism 8. Results: The LSLCs of Permethrin with mortality rates not significantly (P> 0.05) different from control Kisumu strains (0.00) were 0.2μg (0.00) and 0.4μg (0.00) per CDC bottle, i.e., LSLC 1 and LSLC 2 respectively. The LSLC 1 exposure lasted five generations (f0-f4), during which resistance statuses were consistently below 1.00±0.82 (4.0%) after 1 hour. There was no significant difference (P>0.05) in the levels of esterase across generations, while monooxygenase and GST levels were significantly up-regulated (P<0.05) in subsequent generations of LSLC 1-treated mosquitoes. However, there was a consistent and progressive increase in GST level with advancing generations. Conclusion: It may be concluded that the P450 monooxygenase enzyme mechanism is a prelude to the overexpression of the GST enzyme. Hence, if the development of the GST resistance enzyme can be inhibited or stopped in An. gambiae mosquito vector populations, multiple resistance and cross-resistance mechanisms in malaria vectors could be effectively regulated.