Evaluation of Culex Mosquito Susceptibility to Organophosphate, Carbamate and Pyrethroid insecticides in Minna, Nigeria

Abstract

Culex mosquito, an arboviral and filarial vector, is a common breed in Nigeria and other West Africa countries. The different classes of insecticides for this vector control are constantly prone to resistance problem. The present study assessed the susceptibility of culex mosquito to six World Health Organisation (WHO) recommended insecticides of three different classes. Culex mosquito larvae were collected from six different breeding sites within Minna, Niger state, Nigeria and were reared to adults in the insectary. The percentage knockdown and mortality for the adult mosquitoes were evaluated for bendiocarb and propoxur (carbamates); malathion and pirimiphos (organophosphates); permethrin and deltamethrin (pyrethroids) insecticides using WHO standard protocol. Total proteins of adult mosquitoes (dead and alive) were determined by Bradford method and Glutathione-s-transferase (GST) enzyme activity was evaluated using Randox assay kit. The highest breeding site for culex mosquito was the rice fields (36.0 %), while the lowest was in tyres (7.5 %). Gutters, dam, streams and rainpools had 21.6, 12.6, 11.6 and 10.7 (%) respectively. The percentage knockdown (30 minutes exposure time), with deltamethrin, permethrin, bendiocarb, propoxur, malathion and pirimiphos were 76.7, 91.9, 100.0, 72.6, 81.8 and 87.0 (%) respectively. The highest mortality (1hour after exposure) was achieved with bendiocarb (100 %), permethrin (95.1 %), pirimiphos (87.8 %), malathion (86.2 %), deltamethrin (79.0 %) and propoxur (73.1 %). The total proteins of dead mosquitoes were higher than in those alive after exposure to test insecticides. The highest GST activity of mosquitoes alive after exposure was with deltamethrin (728.0 µmol/min/mL), followed by permethrin (713.3 μmole/min/mL, malathion (546.3 μmole/min/mL), pirimiphos (447.4 μmole/min/mL), propoxur (272.2 μmole/min/mL) while dead mosquitoes after exposure to permethrin had the lowest activity (66.3 μmole/min/mL). In conclusion, Culex mosquitoes from the areas tested are resistant to the recommended insecticides except to bendiocarb also GST appears to be the detoxifying enzyme responsible for the resistance.