Abstract
Oxidative stress plays numerous biological roles, both functional and pathological. The role of oxidative stress in various epidemiologically relevant biological traits in Anopheles mosquitoes is not well established. In this study, the effects of oxidative stress on the longevity and insecticide resistance phenotype in the major malaria vector species An. arabiensis and An. funestus were examined. Responses to dietary copper sulphate and hydrogen peroxide were used as proxies for the oxidative stress phenotype by determining the effect of copper on longevity and hydrogen peroxide lethal dose. Glutathione peroxidase and catalase activities were determined colorimetrically. Oxidative burden was quantified as protein carbonyl content. Changes in insecticide resistance phenotype were monitored by WHO bioassay. Insecticide resistant individuals showed an increased capacity for coping with oxidative stress, mediated by increased glutathione peroxidase and catalase activity. This effect was observed in both species, as well as in laboratory strains and F1 individuals derived from wild-caught An. funestus mothers. Phenotypic capacity for coping with oxidative stress was greatest in strains with elevated Cytochrome P450 activity. Synergism of oxidative stress defence enzymes by dietary supplementation with haematin, 3-Amino-1, 2, 4-triazole and Sodium diethyldithiocarbamate significantly increased pyrethroid-induced mortality in An. arabiensis and An. funestus. It is therefore concluded that defence against oxidative stress underlies the augmentation of the insecticide resistance phenotype associated with multiple blood-feeding. This is because multiple blood-feeding ultimately leads to a reduction of oxidative stress in insecticide resistant females, and also reduces the oxidative burden induced by DDT and pyrethroids, by inducing increased glutathione peroxidase activity. This study highlights the importance of oxidative stress in the longevity and insecticide resistance phenotype in malaria vectors.
Highlights
An inevitable consequence of aerobic physiology and metabolism is oxidative stress
As the insecticide resistant SENN DDT strain coped better with oxidative stress than their susceptible SENN counterparts, it was decided to examine the effect of insecticide-induced oxidative stress on exposure survivors
In terms of the oxidative burden induced by insecticide exposure, all four insecticides induced a significant increase in protein carbonyl content compared to the control (1-way ANOVA: p
Summary
An inevitable consequence of aerobic physiology and metabolism is oxidative stress. This particular form of metabolism results in the formation of unstable and reactive intermediates of oxygen known as reactive oxygen species (ROS). ROS are needed for several crucial biological functions, but excessive amounts of these molecules result in a state known as oxidative stress [1]. Flying and haematophagous insects are subject to some of the greatest levels of oxidative stress in the animal kingdom [3]. In haematophagous insects including mosquitoes, blood ingestion induces oxidative stress as a consequence of the release of iron during the digestion of haemoglobin [4]
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