Desenvolvimento de Larvicida Sustentável à Base do Líquido da Casca da Castanha de Caju Técnico: Caracterização Físico-Química e Avaliação de Eficácia sobre o Aedes aegypti

Abstract

Mosquitoes pose a threat to public health and the economy, especially in tropical regions. Aedes aegypti stands out for its high adaptability and rapid reproduction, making it difficult to control, traditionally based on chemical insecticides. However, the vector's growing resistance requires sustainable alternatives, such as the use of agro-industrial waste with larvicidal potential. Technical cashew nut shell liquid (tCNSL), rich in bioactive compounds, has emerged as a promising option, but its oily nature requires chemical modifications to enable its dilution in water, the medium of mosquito larvae. This work aimed to synthesize a sustainable bioproduct based on tCNSL with water-soluble properties and larvicidal activity. Initially, the solubility and larvicidal efficacy of tCNSL and its neutralized derivative (NatCNSL50) were evaluated in combination with different surfactants (Tween 80, Span 80, Sodium Lauryl Sulphate (SLS) and Cetyltrimethylammonium Bromide). SLS, in combination with tCNSL, was identified as the most efficient surfactant, allowing the synthesis of a soluble nanoemulsion (LtCNSL) with larvicidal activity. In order to better understand the properties of the product, the physicochemical characterization of LtCNSL was carried out, including analyses of surface tension, electrical conductivity, zeta potential, hydrodynamic diameter of the micelles, PDI, scanning electron microscopy (SEM), Tyndall effect, absorption, fluorescence intensity and infrared. Its biological activity was also assessed by determining the lethal concentration of 50% (CL50) and 90% (CL90) of 3rd and 4th stage Ae. aegypti larvae, both in laboratory conditions and in the field on a small scale. In addition, confocal fluorescence and SEM images were used to assess the distribution of the bioproduct and damage to the larvae's bodies. The results showed that the nanoemulsion of tCNSL and SLS resulted in a bioproduct (LtCNSL) that was soluble and active on the larvae. The zeta potential indicated greater stability of the product diluted at 10 ×, while the Tyndall effect confirmed the presence of dispersed particles in colloidal solution. Hydrodynamic size characterization revealed nanometric micelles, and fluorescence confirmed emission in the visible light spectrum. The larvicidal activity tests showed the product's efficacy in the laboratory and in the field, with CL50-24 h of 9.59 and 6.59 mg/L, respectively. Confocal microscopy analyses revealed that the LtCNSL bioproduct accumulates in the digestive and excretory systems of the larvae. In addition, SEM images showed predominant changes in the cephalic zone and tegument of the larvae, which may have favored the growth of biofilms throughout the organism. These results highlight the solubility and potential of LtCNSL as a sustainable and effective alternative for controlling Ae. aegypti, offering an innovative solution for vector control programs.