Exposure of malaria vector larval habitats to domestic pollutants escalate insecticides resistance: experimental proof

Poor domestic waste management in unplanned urban areas have resulted into formation of polluted potential malaria vector larval habitats. Most of these larval habitats are contaminated with domestic pollutants such as hydrogen peroxide and detergents. The present study was designed to evaluate the susceptibility status of Anopheles gambie and Anopheles arabiensis to commonly used insecticides after being exposed to hydrogen peroxide and soap detergents in northern Tanzania. Anopheles gambiae s.s larvae were collected from the laboratory colony whereas those for An. arabiensis were sampled from the rice field in lower Moshi. The larvae were reared in two arms, larval habitats in arm one had water containing soaps while in arm two, the larval habitats contained hydrogen peroxide at different concentrations (0.001%, 0.0001%,0.00001% and 0.000001%). Emerging adult’s female of the two Anopheles species from the two larval habitats were exposed to 0.75% and 0.05% of permethrin and deltamethrin WHO Insecticides impregnated standard papers. Knockdown rates were observed for 1 h and mortality rates within 24 h after exposure. Regression analysis was performed using probit analysis to establish knockdown rates and lethal concentration for 50% and 95%. The wild and laboratory anopheles populations reared in detergent or hydrogen peroxide in different concentrations showed reduced susceptibility to permethrin and deltamethrin. The median knockdown time for 50% of the population (KDT₅₀) ranged between 13.52 min (10.98–19.74) to 30.67 min (28.53–34.34) while the KDT₉₅ raised between 32.01 min (29.47–38.23) to 111.84 min (109.70–115.54) for those reared in detergent and exposed to deltamethrin and permethrin. For those reared in hydrogen peroxide and exposed to deltamethrin and permethrin, KDT₅₀ ranged between 8.24 min (6.92–13.51) to 24.28 min(22.70–27.46) while KDT₉₅ ranged between 25.94 min(24.62–31.21) to 118.68 min(117.10–121.86). Mortality of wild population exposed to standard insectides treated papers after reared in detergent ranged between 40 to 95.3% while for those reared in hydrogen peroxide ranged between 67 to 95.3%. The findings of this study demonstrate that domestic waste pollutants such as hydrogen peroxide and soaps are partly associated with reduced susceptibility to insecticides among potential malaria vectors.