Abstract
Metal exposure is one of the commonest anthropogenic pollutants mosquito larvae are exposed to, both in agricultural and urban settings. As members of the Anopheles gambiae complex, which contains several major malaria vector species including An. arabiensis, are increasingly adapting to polluted environments, this study examined the effects of larval metal exposure on various life history traits of epidemiological importance. Two laboratory strains of An. arabiensis, SENN (insecticide susceptible) and SENN DDT (insecticide resistant), were reared in maximum acceptable toxicity concentrations, (MATC—the highest legally accepted concentration) of cadmium chloride, lead nitrate and copper nitrate. Following these exposures, time to pupation, adult size and longevity were determined. Larvae reared in double the MATC were assessed for changes in malathion and deltamethrin tolerance, measured by lethal time bottle bioassay, as well as changes in detoxification enzyme activity. As defence against oxidative stress has previously been demonstrated to affect the expression of insecticide resistance, catalase, glutathione peroxidase and superoxide dismutase activity was assessed. The relative metal toxicity to metal naïve larvae was also assessed. SENN DDT larvae were more tolerant of metal pollution than SENN larvae. Pupation in SENN larvae was significantly reduced by metal exposure, while adult longevity was not affected. SENN DDT showed decreased adult size after larval metal exposure. Adult insecticide tolerance was increased after larval metal exposure, and this effect appeared to be mediated by increased β-esterase, cytochrome P450 and superoxide dismutase activity. These data suggest an enzyme-mediated positive link between tolerance to metal pollutants and insecticide resistance in adult mosquitoes. Furthermore, exposure of larvae to metal pollutants may have operational consequences under an insecticide-based vector control scenario by increasing the expression of insecticide resistance in adults.
Highlights
Human activity has led to a large-scale increase in various environmental pollutants
Members of the Anopheles gambiae complex are known to breed in unpolluted, temporary bodies of water [7]
These include important malaria vector species that have adapted to these polluted environments [8, 11, 12] and these adaptations are likely to affect life history traits of epidemiological importance [2, 13]
Summary
Human activity has led to a large-scale increase in various environmental pollutants. Pollution in rural and urban environments typically leads to an increase in heavy metal contamination. Mining is a source of urban metal pollution that has the potential to cause widespread contamination by runoff and rainwater seepage into water systems [4]. Rural areas are not commonly associated with metal pollution, the use of phosphate fertilizers can contribute to the increase of hazardous heavy metal trace elements [6]. Metal pollution is highly pervasive wherever human activity occurs. These heavy metal contaminants have a tendency to pollute water sources [4] and this has numerous environmental and public health consequences
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