Larval Productivity and Detoxification Enzymes Profile in Response to Physico-chemical Environmental Factors of Anopheles gambiae Breeding Ecologies in Nigeria

Aim: The aim of this study is to investigate Anopheles gambiae larval tolerance, density- as a function of survivorship- and the response of their detoxification enzymes to levels of various physico-chemical environmental factors present in their breeding sites.
Study Design: Mosquito breeding sites were grouped into three different study zones A, B & C on the basis of human related activities (intensive agriculture, petrochemical industries and domestic activities, respectively) taking place within and/or around the breeding sites, followed by sampling of An. gambiae larvae and determination of larval density from all the breeding sites across the designated study zones. Some of the sampled larvae were reared into pupae and adult. 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 mosquito breeding sites across the three study zones. Activities of the 3 major detoxification enzymes (P450, GST and α & β-esterases) were assayed on the sampled larvae and the emerged pupae and adult.
Results: Our results showed high degree of tolerance of An. gambiae larvae to higher levels of these environmental factors. Also, the activities of the detoxification enzymes were higher in study zones A & C (which also recorded higher levels of the environmental factors) and were highly associated with most of the physico-chemical environmental factors. A deduced statistical model established the chemical composition in combination with some of the physical environmental parameters as influencing factors for larval density and producing an inductive effect on the three detoxification enzymes across the three life stages.
Conclusion: These observations could have a significant impact on the environmental management and insecticide-based approach to vector control in Nigeria.