Effects of phytochemicals in nectar on the insecticide resistance of the mosquito Anopheles gambiae

Although nectar is the main energy source for mosquitoes, it contains phytochemicals with pro- or antioxidant activity that may affect insecticide susceptibility. Here, we assess how sugars and nectar-associated phytochemicals modulate mosquito responses to insecticides. In a first experiment, newly emerged mosquitoes were fed sucrose, glucose, fructose, or trehalose at low (1.97 kcal/100 ml) or high (19.7 kcal/100 ml) concentrations and exposed at four days of age to 0.5% deltamethrin. Mortality within 24 h was higher at the low concentration (87.1%) than at the high concentration (59.2%). Trehalose induced the highest mortality (84.1%), followed by fructose (74.1%), sucrose (67.9%), and glucose (67.1%). In a second experiment, mosquitoes fed 10% glucose supplemented with caffeine (0, 50, or 200 ppm) showed a dose-dependent increase in mortality after exposure to 0.25% deltamethrin, rising from 11.4% to 41.0%. In a third experiment, mortality increased in the absence of vitamin C (32.5% vs 20.4%) and in the presence of hydrogen peroxide (34.6% vs 18.1%). Overall, these results demonstrate that sugars and nectar-derived phytochemicals strongly modulate insecticide sensitivity, highlighting novel opportunities for improving vector control strategies.