Insecticide resistance in selected culex mosquito species in Sri Lanka

Abstract

Culex mosquitoes are widely distributed with a broader host range and are possible vectors of emerging infectious diseases. Thus, continuous assessment of their responses to mosquito control approaches is essential. This study aimed to determine the insecticide resistance mechanisms of Culex quinquefasciatus, Cx nigropunctatus and Cx sitiens in Sri Lanka. Mosquito samples were collected from Kandy, Kurunegala and Puttalam districts. Collected samples were tested to determine the activity levels of detoxifying enzymes and Acetylcholinesterase insensitivity to Organophosphates and Carbamates. Biochemical assays were conducted according to the procedures outlined by the World Health Organization. From each population >200 mosquitoes were subjected to Protein, Esterase (ES), Glutathione-S-transferase (GST), Monooxygenase (MO), and Acetylcholinesterase (ACE) assays. Relatively high specific activity levels of ES (1.01±0.2 μmol mg⁻¹ min⁻¹) and remaining activity levels of ACE (87.05±15.12%) were reported from Cx quinquefasciatus from Kurunegala. Specific activity levels of GST for Cx quinquefasciatus populations from Kurunegala and Peradeniya were 0.63±0.09 and 0.6±0.11 μmol mg-1 min⁻¹, respectively. A relatively high activity level of MO (0.23±0.12 μmol mg⁻¹ min⁻¹) was reported from Cx quinquefasciatus from Peradeniya. Cx sitiens population, which was collected from forested habitats, showed relatively less activity levels for ACE (67.63±18.72%), GST (0.44±0.14 μmol mg⁻¹ min⁻¹) and ES (0.72±0.26 μmol mg⁻¹min⁻¹ ). Cx nigropunctatus populations reported moderate activities for all tested enzymes. A significantly high enzyme activity levels of Cx quinquefasciatus (p<0.05) populations suggested the relatively high resistance developed by these mosquito populations to all insecticide groups.