Response of <i>Anopheles gambiae</i> detoxification enzymes to levels of physico-chemical environmental factors from northwest Nigeria

Abstract

The objective of this study was to investigate the response of Anopheles gambiae detoxification enzymes to levels of various physico-chemical environmental factors present in their breeding sites. Mosquito breeding sites were grouped into three different breeding sites (designated as study zones A, B & C) on the bases of human related activities (intensive agriculture, petrochemical and domestic) taking place within and/or around the breeding sites, followed by sampling of Anopheles gambiae larvae from all the breeding sites across the designated study zones. Some of the sampled larvae were reared to pupae and adult life stages. Levels of 7 physical (pH, temperature, conductivity, transparency, total dissolved solids, dissolved oxygen and biological oxygen demand) and 6 chemical (sulphates, phosphates, nitrites, nitrates, carbon content and oil and grease) environmental factors were determined from these mosquito breeding sites. Activities of the 3 major detoxification enzymes (Cytochrome P450 oxygenase, GST and α & β-esterases) were evaluated in the sampled larvae as well as the pupae and adult samples that ultimately emerged from the larvae. Following statistical analysis, results showed that P450 activities were higher in the petrochemical sites (zone C) and the activities were highly associated with pH, temperature as well as carbon content and oil and grease. The activities of GST and α & β- esterases were higher in the intensive agriculture sites (Zone A) and were highly correlated with all the chemicals environmental factors. A deduced statistical model established all the chemical in combination with some of the physical environmental factors as producing an inductive effect on these three detoxification enzymes. These observations could have a significant impact on the insecticide-based approach to vector control. An. gambiae samples may have developed intrinsic enzymatic machinery to produce an adaptive tolerance to various insecticides used for their control since most of these insecticides and the environmental chemical factors share similar routes of metabolism.

Keywords: Cytochrome, Anopheles, Inescts, Northwestern Nigeria