Estudo da fotoinativação de larvas de Aedes aegypti (LINNAEUS, 1762) com formulações de curcumina: eficácia e segurança ambiental

Abstract

The selection of resistant populations of the vector Aedes aegypti to traditional chemical insecticides has motivated the search for alternative techniques to control the proliferation of vector mosquitoes. Photodynamic inactivation (PDI) is a promising tool against vector Ae. aegypti, involving the combination of three elements: specific wavelength, photosensitive molecule (PS) and molecular oxygen, which when associated cause irreversible damage. Ambient temperature is an important factor in the survival of larvae and mosquitoes, as it influences their physiology, behavior and ecology. This study aimed to evaluate curcumin-based formulations for PDI of Ae. aegypti larvae under laboratory and simulated field conditions. The implementation was carried out in stages: (i) the biological cycle parameters of Ae. aegypti, such as hatching rate and lethal concentration (LC) of larvae and mortality promoted by PDI with curcumin, under different temperatures (20, 25, 30 and 35 °C). (ii) formulation and characterization of microencapsulated curcumin by ultraviolet-visible (UV-Vis) absorption spectroscopy, scanning electron microscopy (SEM), confocal microscopy, and Fourier transform infrared spectroscopy (FTIR), and biological assays with larvae. Lethal concentrations (LCs50;90) for IFD action in the laboratory were defined. (iii) evaluation of the photodynamic action behavior in a simulated field, based on the LCs determined in the laboratory, evaluated larval mortality and the persistence of the curcumin-based formulation. (iv) ecotoxicological analyses with non-target organisms (Danio rerio, Allium cepa, and Galleria mellonella). The results of step i) indicated that higher temperatures result in higher larval mortality at lower concentrations of the curcumin formulation. The larvae that survived after PDI, when compared to the control groups, showed delayed development. The survival evaluation of adult male and female mosquitoes for the control and PDI groups showed a reduction in the longevity of mosquitoes in the PDI group compared to the control. In step ii), the curcumin microcapsule presented an absorption peak at 440 nm, an average size of 11.1 ± 3.1 µm, and there were no significant shifts in the positions of the characteristic bands of curcumin and its excipients. Furthermore, it maintained its efficacy, and laboratory results show that the LCs were 0.27 mg/L (LC50) and 1.6 mg/L (LC90), respectively. Step (iii), in a simulated field, the concentrations obtained were LC50 2.30 mg/L and LC90 8.7 mg/L, respectively. The results of the persistence evaluation of the curcumin microcapsule in a simulated field showed 100% efficacy for up to 20 days, with activity declining over time, completely losing its efficacy after 45 days. In stage IV, the ecotoxicity evaluation showed no toxicity to non-target organisms: Danio rerio (100 mg/L), Allium cepa (100 mg/L) and Galleria mellonella (2000 mg/L). The photodynamic action is effective in laboratory and simulated field tests. Therefore, the curcumin-based photolarvicide may be a potential integrated control agent for the Ae. aegypti vector in the larval stage and, consequently, for reducing arbovirus transmission.