Insecticide Resistance Status of Anopheles Gambiae (Diptera: Culicidae) In Selected Vegetable Growing Areas and Non-Vegetable Growing Areas in Accra Metropolis, Southern Ghana.

Abstract

The spread of insecticide resistance in Anopheles gambiae constitutes a major impediment to the effectiveness of malaria insecticide-based control tools and this is intensified by the use of the same insecticides in controlling both agricultural pests and public health vectors. The aim of this study was to establish the status of insecticide resistance in Anopheles gambiae found in vegetable growing areas (Korle-Bu and Opeibea) and non-vegetable growing areas (Mataheko and Achimota) and to determine the factors responsible for the selection of An. coluzzii and An. gambiae s.s. at the study sites. WHO susceptibility test procedures using five insecticides viz: Deltamethrin, Permethrin, Malathion, DDT and Bendiocarb was conducted in addition to a synergist (PBO) assay to assess the insecticide resistance status of An. gambiae s.l. population within the vegetable growing areas in comparison to the non-farming sites. Resistance was relatively high in both the farming and non-farming areas, but the exposure to PBO also enhanced the mortality of An. gambiae s.l. in all the sites. All the wild mosquitoes were identified to be Anopheles gambiae s.s. Korle-Bu had a dominance of 97.5 % An. coluzzii, while Opeibea had a dominance of 95 % An. gambiae s.s. and this was attributed to the ecological distribution and nature of the larval breeding water. The two species were found living in sympatry in the non-farming sites. High frequency of kdr and ace-1 gene mutation in mosquitoes were recorded from all the sites with the highest frequencies obtained from mosquitoes collected at Opeibea. A higher frequency of kdr and ace-1 gene mutation was recorded in An. gambiae s.s. than in An. coluzzii. Significantly higher enzyme activities were detected in the wild strains of An. gambiae s.l. compared to the susceptible Kisumu strain in all the sites except for glutathione-S-transferase (GST), where no difference was observed. Insecticide residues were determined using the gas chromatography (GC) method after fractionation of the extracts using solid phase extraction (SPE). All the samples from the study sites were found to contain detectable levels of chlorpyrifos, while dichlorodiphenyldichloroethylene (p, p`-DDE) was only detected in vegetable growing areas of Korle-Bu and Opeibea. The detection of pesticide residues in the larval breeding water in both vegetable and non-vegetable growing areas; high frequencies of the kdr and ace-1 gene mutations in all the sites; and elevated levels of enzyme activities in the mosquitoes from all the sites, revealed presence of insecticide resistance in Anopheles gambiae mosquitoes from the four study areas. This suggests that both agricultural activities and public health practices contribute to resistance in Anopheles gambiae in Accra. Enhancement of susceptibility to Deltamethrin and Permethrin in all the sites indicates the involvement of P450’s in the development of resistance in the mosquitoes. Therefore, vector control products prepared with PBO can be effective even in the presence of pyrethroid resistance. Generally, resistance was only relatively higher in vegetable growing areas than non-vegetable growing areas although, was not statistically significant (p > 0.05). It was mostly driven by the application of insecticides by the farmers to control agricultural pest. However, more studies are recommended in other urban vegetable growing areas to understand the full scale of the impact of agricultural pesticides in the development of resistance in An. gambiae s.l.