Larvicidal and histological effects of Melia azedarach extract on Culex quinquefasciatus Say larvae (Diptera: Culicidae)

Extracts from Melia azedarach L. (Meliaceae) were effective against third instar larvae of Culex quinquefasciatus (Say) in Saudi Arabia, using crude extract obtained in ethanolic solution from King Saud University. Toxicity was varied according to the concentration and period of exposure. We investigated the effect of the LC50 on midgut and gastric caecae of 3rd larval instar of Cx. quinquefasciatus, the plant extract causing serious damage to the epithelial columnar cells. Light and electron microscopic observations revealed, by time 6, 12, 24 and 48 h, increasing damages of the larvae midgut epithelium. The most characteristic effects were midgut columnar cell vacuolization, microvilli damages, epithelium cell contents passing into the midgut lumen and finally the cell death. This article is the first report of the histopathological effects of the M. azedarach as a bioinsecticide in the midgut of Cx. quinquefasciatus larvae and the data obtained may contribute to a better understanding of the mode of action of this plant extract used as a bioinsecticide against Cx. quinquefasciatus larvae.