Malaria is an infectious disease caused by protozoan parasites of the genus Plasmodium, which are transmitted among humans by mosquitoes of the genus Anopheles. The aim of this study was to assess the repellent effects of dillapiol isolated from Piper aduncum and its nanostructured formulations against adult Anopheles darling mosquitoes. It was also assessed the synergistic effect when it was associated with the chemical insecticides deltamethrin, cypermethrin, and alfa-cipermetrin, as well as the effect of topical application of such compounds. The oil was extracted from leaves using the technique of steam distillation conducted in Clevenger apparatus; dillapiol was isolated by column chromatography. Dillapiol oil and chemical insecticides were nanocoated with PLA and PLGA polymers. Nanocapsule morphology was analyzed by Scanning Electron Microscopy – SEM. For repellency tests, dillapiol pure oil was used both in conventional form (an amount of 0.762 g) and nanocoated (an amount of 0.865 g). In this assay, 25 volunteer couples placed simultaneously their treated and untreated arms within net cages containing 50 A. darlingi female mosquitoes each. Regarding the wall bioassays, they were carried out according to the procedure standardized by the World Health Organization – WHO. The basic material was constituted of a kit of cone chambers model (VBC/ 81.5), which was attached to wooden boards impregnated with both nanocoated samples and commercial insecticides. Regarding the topical application, every nanocoated sample was sprayed into three cages containing ten mosquitoes each, by means of a paint gun attached to a compressor. The results from the repellency tests of nanocoated samples, containing the Sepigel and Carbopol 0.7 % carriers and dillapiol revealed effectiveness at every time interval analyzed. The number of bites observed at the treated arm was significantly lower than at the untreated one. It was also significant that the number of bites depended on the interaction between substance and time. Dillapiol nanocapsule containing 0.7 % Carbopol carrier showed a greater repellency potential amongst the nanocoated samples analyzed. The lack of significant difference was observed when using dillapiol pure oil, whose repellency was effective up half an hour after application. Wall bioassay showed the effectiveness of nanocoated samples in relation to commercial ones, also indicating a synergistic potential when associated nanocapsules were analyzed. The evaluation of synergistic potential of nanocoated dillapiol and its combinations with pyrethroids indicated the efficacy of this compound as an alternative to reduce the amount of chemicals used in the field, especially in intra-home spraying. Scanning electron microscopy analysis showed that the nanoparticles kept attached to the nervures of mosquito wing scales, and are promising alternatives to synthetic chemicals, when regarding intra-home spraying. The results of this study are an indicative that dillapiol – be nanocoated or pure oil – is a viable alternative to be used as a repellent against malaria mosquitoes. The use of dillapiol nanostructured formulations in combination with pyrethroids demonstrate the synergistic potential that these compounds have against Anopheles darlingi, the main vector of human malaria in the Amazon.
