Spent Coffee Grounds and Novaluron Are Toxic to Aedes aegypti (Diptera: Culicidae) Larvae

SIMPLE SUMMARY: The mosquito Aedes aegypti has developed insecticide resistance in Thailand and around the world. We investigated the effective forms between wet and dry spent coffee grounds (wSCGs and dSCGs) and novaluron on larval mortality and adult emergence inhibition of Ae. aegypti. The main chemical compound concentration in wSCGs was higher than that in dSCGs. Then, the effective SCGs were selected to combine with novaluron and determined the synergistic effects of its combination. At sublethal concentrations wSCGs and novaluron had low efficacies when present individually; however, when combined at low concentrations, they showed greater efficacy. Therefore, wSCGs combined with novaluron could be utilized as an alternative control for this mosquito vector. ABSTRACT: Aedes aegypti (Diptera: Culicidae) is a vector for mosquito-borne diseases worldwide. Insecticide resistance is a major concern in controlling this mosquito. We investigated the chemical compounds in wet and dry spent coffee grounds (wSCGs and dSCGs) and evaluated the efficacy of dSCGs, wSCGs, and novaluron on the mortality and adult emergence inhibition of Ae. aegypti. We found higher concentrations of chemical compounds in wSCGs than in dSCGs. The wSCGs and dSCGs both contained total phenolic compounds, total flavonoid compounds, caffeic acid, coumaric acid, protocatechuic acid, and vanillic acid. Complete mortality was observed after 48 h of exposure to 50 g/L wSCGs, while similar mortality was found after 120 h of exposure to 10 µg/L of novaluron. The sublethal dose was a concentration of wSCGs (5 g/L) and novaluron (0.01, 0.1, and 1 µg/L) combined that resulted in a larval mortality lower than twenty percent (at 72 h) to determine their synergistic effects. The death rate of larvae exposed in sublethal combination of wSCGs and novaluron was significantly higher than that of its stand-alone. The findings indicate that the combination of wSCGs and novaluron at sublethal concentrations had synergistic effects on the mortality of Ae. aegypti larvae and could be applied as an alternative control measure.