Avaliação da atividade repelente de derivados a base de octenol e ácido lático contra fêmeas do mosquito Aedes (Stegomyia) aegypti (Linnaeus, 1762) (Diptera: Culicidae)

Abstract

The use of repellents is an individual protective measure aimed at reducing human contact with the vector. These are volatile chemicals detected by the sensory receptors of female Aedes aegypti mosquitoes, which leave them disoriented and prevent their bites. The objective of this study was to evaluate the repellent activity of eight derivatives: three based on lactic acid (RSD36, RSD38, RSD48) and five based on octenol (RSD44, RSD45, RSD46, RSD47, RSD49). The study assessed their duration of protection, compared those showing repellency with a commercial 25% DEET repellent used as a control, and also evaluated them with human volunteers. The study was conducted at the Malaria and Dengue Laboratory (LMD) in partnership with the Department of Chemistry at the Federal University of Paraná (UFPR), responsible for developing, producing, and sending the derivatives to LMD. The derivatives were labeled with codes to prevent identification by the applicator. Six volunteers over 18 years old, of both sexes, participated and signed an Informed Consent Form. All volunteers underwent allergy tests for the eight octenol and lactic acid derivatives, as well as the commercial 25% DEET repellent, with no allergic reactions observed. Before testing, volunteers washed their hands with neutral detergent and dried them with clean disposable paper towels. The study began with a negative test where neither hand had any product applied, to observe the mosquitoes' activity. Subsequently, 1 g of commercial 25% DEET repellent was applied to the right hand (control), and 100 µl of each derivative diluted in 900 µl of ethanol (totaling 1 mL) was applied to the left hand (test). After both applications, a 5-minute waiting period allowed for evaporation. Two cages were used, one labeled "control" and the other "test," each containing 30 A. aegypti females aged 3 to 9 days, fed only a 10% sucrose solution. Testing involved inserting the right hand into the control cage for three minutes, followed by the same procedure with the left hand in the treatment cage. There was a one-hour interval between evaluations to assess repellent activity, duration of protection compared to the commercial 25% DEET, percentage of protection conferred to each volunteer, and differences in protection time among volunteers. During evaluation, observations included the mosquitoes' feeding behavior or attempts to bite or land on the hand for up to 5 seconds. Immediate cessation of the test occurred upon such events, deemed repellent failure; otherwise, evaluations continued for three minutes, concluding with repellent activity. Among the eight derivatives tested, two lactic acid-based derivatives showed repellent activity. RSD38 provided a maximum protection of 560 minutes compared to 630 minutes for its control. RSD48 showed 318 minutes of maximum protection compared to 478 minutes for its control. Statistical analyses did not reveal significant differences between the protection times of RSD38 and RSD48 and their respective controls, despite the longer protection times of the controls. In conclusion, this new strategy could complement existing vector control measures, potentially leading to a product that reduces female A. aegypti mosquito bites and consequently arboviral disease cases in the future.