Insecticidal and Histopathological Effects of <i>Ageratum conyzoides</i> Weed Extracts against Dengue Vector, <i>Aedes aegypti</i>

• Main Authors: Ai-rada Pintong, Sumate Ampawong, Narumon Komalamisra, Patchara Sriwichai, Supaluk Popruk, Jiraporn Ruangsittichai
• Format: Article
• Language: English
• Published: MDPI AG 2020-04-01
• Series: Insects
• Subjects: Asteraceae; <i>Aedes</i>; essential oils; crude extracts; insecticide; pesticide
• Online Access: https://www.mdpi.com/2075-4450/11/4/224

Crude extracts and essential oils of <i>A. conyzoides</i> were tested with larva and adult stages of <i>Ae. aegypti</i> mosquitoes to determine their insecticidal properties. The crude extracts and essential oils came from three varieties of <i>A. conyzoides</i> (with white flowers, purple flowers, or white-purple flowers) and from two places on each plant (leaves and flowers), giving six types overall: leaf-white (LW); leaf-purple (LP); leaf white-purple (LW-P); flower-white (FW); flower-purple (FP); and flower white-purple (FW-P). Chemical constituents and components of the essential oils were identified using gas chromatography-mass spectrometry (GC-MS). Electron microscopic and histopathological studies were performed to determine the toxicological effects on mosquitoes in terms of morphological alterations. The six types of crude extracts exhibited no activity against individuals in the larval stages. However, six types of essential oils were effective against adult <i>Ae. aegypti</i> females. The mortality of adult <i>Ae. aegypti</i> females was higher from leaf extracts, particularly LP (median lethal dose, LD₅₀ = 0.84%). The number of chemical constituents identified by GC-MS was high in flowers, especially W-P. Precocene I was the most abundant chemical component among the five types of essential oils, except in LP, in which precocene II was the most abundant. Histopathological alterations in adult <i>Ae. aegypti</i> females included compound eye degeneration, muscular damage with cellular infiltration, gut epithelial degeneration and necrosis, pyknotic nuclei in the malpighian epithelium and ovarian cell degeneration. FW and FP plant types exhibited the highest severity of histopathological alterations in mosquitoes compared with other plants, probably owing to the presence of monoterpene compounds in their tissues. The present study demonstrated LP plant extracts from <i>A</i>. <i>conyzoides</i> could be effective adulticides against adult <i>Ae</i>. <i>aegypti</i>. As natural products are biodegradable and exhibit low toxicity to mammalian and non-target organisms, they are suitable candidates for use in vector control programmes.