Larvicidal efficacy of Varronia curassavica leaf phytochemicals against Aedes aegypti: anatomical, histological and cytotoxic analyses.

Aedes aegypti, the primary vector of diseases like Dengue, Zika, Yellow Fever, and Chikungunya, presents a significant public health challenge, particularly in tropical regions. With rising resistance to conventional insecticides, plant-derived bioinsecticides have emerged as a promising alternative. This study assessed the larvicidal potential of phytochemicals from Varronia curassavica, a species native to the Atlantic Forest. Microscopic analyses revealed various trichome types on V. curassavica leaves, including glandular trichomes containing essential oils, phenolic substances, lipids, alkaloids, and pectins and other protein-producing trichomes. Methanolic leaf extracts demonstrated 65 % lethality against third-instar larvae of A. aegypti at 100 ppm. Fractionation of the extract using solvents of increasing polarity identified the dichloromethane (CH₂Cl₂) partition as the most toxic. Further purification of this by silica-gel chromatography produced subfractions, with VCDF11 (Varronia carassavica dichrolometane fraction) showing the highest toxicity (LC50 = 57.0 ppm and LC90 = 74.4 ppm). The VCDF11 fraction was the most active, and subfraction VCDF11.6 exhibited 100 % larvicidal activity. Gas chromatography-mass spectrometry (GC-MS) identified key components, including terpenes (β-copaene, δ-cadinene, phytol) and fatty acids (octadecanol, hexadecanoic acid) in the VCDF11.6 fraction. These compounds disrupted the epidermis, gastric cecum, and larval cuticular layers. An MTT assay confirmed low cytotoxicity of the VCDF11.6 fraction to monkey kidney cells. V. curassavica phytochemicals demonstrate relevant larvicidal activity against A. aegypti larvae with minimal toxicity to mammalian cells, highlighting their potential as a bioinsecticidal agent.