Ecotoxicology and Environmental Safety 70 (2008) 244–250 Highlighted article Effect of azadirachtin on acetylcholinesterase (AChE) activity and histology of the brown planthopper Nilaparvata lugens (Sta˚ l) $ Sengottayan Senthil Nathan a,b,Ã , Man Young Choi a , Hong Yul Seo a , Chae Hoon Paik a , Kandaswamy Kalaivani a , Jae Duk Kim a a Plant Environment Division, Honam Agricultural Research Institute (HARI), National Institute of Crop Science (NICS), Rural Development Administration (RDA), #381 Songhak-dong, Iksan, Chonbuk 570-080, Republic of Korea b Post Graduate and Research Department of Biotechnology, Vivekanandha College (W), Trichengode, Namakkal, Tamil Nadu, 637 205, India Received 29 November 2006; received in revised form 30 June 2007; accepted 12 July 2007 Available online 4 September 2007 Abstract The effect of azadirachtin (AZA), a tetranortriterpene from neem, on the mortality, acetylcholinesterase (AChE) activity, and the development of the ovaries of female brown planthopper (BPH), Nilaparvata lugens (Sta˚l) was tested in laboratory experiments. The lethal concentrations were determined and applied topically to the adult female BPH (LC 50 ¼ 0.47 ppm and LC 90 ¼ 0.96 ppm). The treated insects exhibited toxic symptoms with a dose-dependent mortality. The LC 50 concentrations were tested against AChE activity of the BPH. The results indicate that AZA significantly inhibits the activity of AChE only at the high dose (Po.0001) compared with control. Adult females that were exposed to AZA showed a significant reduction in weight (23%, 40%, and 64% for 0.1, 0.25, and 0.5 ppm, respectively). Fecundity was also significantly reduced in AZA treatments compared to the control. Histological study of ovary sections revealed abnormalities in follicular epithelial cells due to AZA treatment. r 2007 Elsevier Inc. All rights reserved. Keywords: Azadirachtin; BPH; AChE; Enzyme; Histology; Ovary; Follicular epithelial cell 1. Introduction Biopesticides with different modes of action may mini- mize insecticide resistance and pest resurgence problems while being safe and ecologically acceptable (Matthews, 1999; Copping and Menn, 2000; Senthil Nathan et al., 2006a,b). The insecticidal, repellent and antifeedant prop- erties of neem (Azadirachta indica A. Juss) derivatives have been known for three decades (Schmutterer, 1990; Ascher, 1993). Although several potentially insecticidal active ingredients occur in neem seed extract, the principal active ingredient in most formulations is the tetranortriterpene azadirachtin (AZA) (Sundaram, 1996; Senthil Nathan et al., 2005). But the action of AZA against the brown planthopper (BPH), with respect to acetylcholinesterase (AChE) activity, is unknown. AChE-EC 3.1.1.7 is a key enzyme that terminates nerve impulses by catalyzing the hydrolysis of the neurotrans- mitter, acetylcholine, in the nervous system in various organisms (Oehmichen and Besserer, 1982; Wang et al., 2004). It is well known that the altered AChE is one of the main resistance mechanisms in many insect pests. Insensi- tivity of AChE observed in organophosphorous or carbamate-resistant insects has been well documented for various insect pests (Hama, 1983; Hemingway et al., 1986; Yoo et al., 2002; Wang et al., 2004). Organophosphorous insecticides, such as diazinon, target AChE and irreversibly ARTICLE IN PRESS www.elsevier.com/locate/ecoenv 0147-6513/$ - see front matter r 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.ecoenv.2007.07.005 Abbreviations: BPH: brown planthopper; AZA: azadirachtin; ACh: acetylcholine; AChE: cetylcholinesterase; LC: lethal concentration; IGR: insect growth regulator; DAG: days after germination $ This paper was given in an abstract form at the Korean Entomolo- gical Society Meeting, Seoul, Korea, 29th September 2006, Abstract 46, p. 114. Ã Corresponding author. Plant Environment Division, Honam Agricul- tural Research Institute (HARI), National Institute of Crop Science (NICS), Rural Development Administration (RDA), #381 Songhak-dong, Iksan, Chonbuk 570-080, Republic of Korea. Fax: +82 63 840 2118. E-mail addresses: senthilkalaidr@hotmail.com, senthil@rda.go.kr (S. Senthil Nathan).