Egypt. Acad. J. biolog. Sci., 4 (1): 33 - 48 (2011) A. Entomology Email: egyptianacademic@yahoo.com ISSN: 1687–8809 Received: 11/2/2011 www.eajbs.eg.net Evaluation of the biological activity of some Cupressus semprevirens (Cupressaceae) extracts against the mosquito vector Culex pipiens L. (Diptera: Culicidae) Tarek M.Y. EL-Sheikh 1 , Mostafa I. Hassan 1 , Walaa A. Moselhy 2 , Mouneer S. Amer 1 and Ahmed Z. Shehata 1 1- Department of Zoology, Faculty of Science (boys), Al-Azhar University, Nasr City, Cairo, Egypt. 2- Department of Zoology, Faculty of Science(girls), Al-Azhar University, Nasr City, Cairo, Egypt. E-mail: Tarek_elshekh2000@yahoo.com ABSTRACT Ethanolic, acetone and petroleum ether extracts of leaves from the Egyptian plant Cupressus sempervirens (Cupressaceae) were tested against 3 rd instar larvae of the mosquito Culex pipiens L. The obtained results indicated that petroleum ether extracts were more efficient than ethanolic and acetone extracts. The toxicity, based on Lc 50 values, are arranged in a descending order as follows: ethanolic (Lc 50 263.6ppm) > acetone extract (Lc 50 104.3ppm) > petroleum ether extracts (Lc 50 37.8 ppm). As shown by the present results, a remarkable reduction in both the pupation percent and adult emergence was obtained. Moreover, all plant extracts exerted a delayed toxic effect on the pupae and adults after treatment of larvae. Also, various degrees of morphogenic abnormalities were observed in the immature and adult stages. Thus, these results may provide an opportunity to develop alternatives to costly organic pesticides and environmentally hazardous chemicals with some available cheap plants which are uaually environmentally safe to different living organisms. Key words: Ethanolic extract, Acetone extract, Petroleum ether extract, Toxicity, Cupressus sempervirens, Culex pipiens, growth, mortality, pupation, emergence, malformation. INTRODUCTION Mosquitoes are vectors of many vertebrate blood parasites. In Egypt, Culex pipiens has a wide distribution and is the main vector of Rift valley fever virus (Darwish and Hoogastrall, 1981), Wuchereria bancrofti (Gad et al., 1996) and Western Nile virus (Pelah et al., 2002). Recently, Hassan et al. (2003) studied the possibility of C. pipiens for the transmission of Hepatitis C virus (HCV). However, such possibility is still under investigation. Insecticide applications although highly efficacious against the target species, vector control is facing a threat due to the development of resistance to chemical insecticides resulting in rebounding vectorial capacity (Liu et al., 2006). Furthermore, they are responsible for substantial hazards to a variety of non-target organisms and environment in the form of biomagnification (Gold et al., 2001). Therefore, researchers have diverted their attention since few decades ago towards the plant world, which are ecofriendly and cost effective. Many studies on plant extracts against mosquito vectors have been conducted around the world, but most of them are restricted to preliminary screening (Prajapati et al., 2005; Shaalan et