Short Communication Effect of neem limonoids on lactate dehydrogenase (LDH) of the rice leaffolder, Cnaphalocrocis medinalis (Guene ´e) (Insecta: Lepidoptera: Pyralidae) Sengottayan Senthil Nathan a,b, * , Kandaswamy Kalaivani b , Paul Gene Chung a , Kadarkarai Murugan b a Department of Environmental Engineering, Chonbuk National University, Jeonju City, Chonbuk 561 756, South Korea b Department of Zoology, Bharathiar University, Coimbatore 641 046, Tamil Nadu, India Received 10 March 2005; received in revised form 25 May 2005; accepted 1 July 2005 Available online 12 September 2005 Abstract Neem is derived from the neem tree Azadirachta indica A. Juss. (Meliaceae), and its primary insecticidal component is the tetranortriterpenoid azadirachtin and other limonoids. The effect of neem limonoids azadirachtin, salannin, deacetylgedunin, gedunin, 17-hydroxyazadiradione and deacetylnimbin on enzyme lactate dehydrogenase (LDH) activ- ity of the rice leaffolder (RLF) Cnaphalocrocis medinalis (Lepidoptera: Pyralidae) larvae was investigated. There was a decrease in enzyme activity relative to the control at all concentrations tested. When fed a diet of rice leaves treated with neem limonoids in bioassays, gut tissue enzyme, LDH levels in rice leaffolder larvae are affected. These results indicate neem limonoids affect LDH activity. These effects are most pronounced in early instar larvae. Azadirachtin was the most potent in of all the limonoids in all experiments indicating strong enzyme inhibition. Clear dose–response relation- ships were established with respect to LDH activity. Ó 2005 Published by Elsevier Ltd. Keywords: Azadirachtin; Salannin; Deacetylgedunin; Gedunin; 17-Hydroxyazadiradione; Deacetylnimbin; Enzyme activity; LDH; Toxicity 1. Introduction Lactate dehydrogenase (LDH) (EC 1.1.1.28) is an important glycolytic enzyme present in virtually all ani- mal tissues (Kaplan and Pesce, 1996). It is also involved in carbohydrate metabolism and has been used to indi- cate exposure to chemical stress (Wu and Lam, 1997; Diamantino et al., 2001). LDH is a parameter widely used in toxicology and in clinical chemistry to diagnose cell, tissue and organ damage. However, the potential of this enzyme as an indicative criterion in invertebrate toxicity tests has been scarcely explored (Ribeiro et al., 1999). The Indian neem tree, Azadirachta indica A. Juss. (Meliaceae), has been found to be a promising source of natural pesticides. Several constitutions of its leaves 0045-6535/$ - see front matter Ó 2005 Published by Elsevier Ltd. doi:10.1016/j.chemosphere.2005.07.009 * Corresponding author. Address: Department of Environ- mental Engineering, Chonbuk National University, Jeonju City, Chonbuk 561 756, South Korea. Tel.: +82 63 270 2444; fax: +82 63 270 2449. E-mail addresses: senthilkalaidr@hotmail.com, senthil@ chonbuk.ac.kr (S. Senthil Nathan). Chemosphere 62 (2006) 1388–1393 www.elsevier.com/locate/chemosphere