Acta Tropica 126 (2013) 249–255 Contents lists available at SciVerse ScienceDirect Acta Tropica journa l h o me pa g e: www.elsevier.com/locate/actatropica Immuno-suppressive effects of aqueous extract of soapnut Sapindus emarginatus on the larvae and pupae of vector mosquito, Aedes aegypti Arunagirinathan Koodalingam 1 , Periasamy Mullainadhan ∗ , Munusamy Arumugam Laboratory of Pathobiology, Department of Zoology, University of Madras, Guindy Campus, Chennai 600025, India a r t i c l e i n f o Article history: Received 24 December 2012 Received in revised form 21 February 2013 Accepted 24 February 2013 Available online 7 March 2013 Keywords: Soapnut Botanical insecticide Insect immunity Hemocytes Phagocytosis a b s t r a c t We recently reported the presence of potent anti-mosquito activity in aqueous kernel extract of the soap- nut, Sapindus emarginatus, and demonstrated its impact on marker enzymes in larvae and pupae of the vector mosquito, Aedes aegypti. As a sequel to these findings, the present study elucidates immunotoxic- ity of this extract with respect to hemocyte-mediated cellular immune responses in fourth instar larvae and pupae as well as cuticular melanization reaction in the larvae of A. aegypti. The exposure of these two developmental stages of the mosquito to the soapnut extract at a lethal threshold concentration neither affected hemocyte viability tested up to 3 h in vitro nor did it influence the hemocyte count. By con- trast, exposure of the mosquito larvae and pupae to this extract significantly reduced the ability of their hemocytes to bind yeast cells, an important early event in the process of non-self recognition by immune cells. Consequently, the phagocytic activity of these hemocytes against yeast cells was also found to be adversely affected upon exposure of larvae and pupae to the extract. Besides, a perceptible initial delay in melanization reaction at the injured site of the cuticle in the extract-exposed larvae was observed. All these findings demonstrate, for the first time, the immuno-suppressive potential of a botanical biocide in the vector mosquito. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Vector-borne diseases impose a challenging problem to pub- lic health particularly in tropical and subtropical countries. Among various invertebrates, mosquitoes are the predominant disease vectors, transmitting a wide range of human pathogens including viruses as well as protozoan and metazoan parasites (Klempner et al., 2007; Herrera et al., 2012). Consequently, these potent pathogens cause several dreadful diseases like malaria, filaria- sis, Japanese encephalitis, yellow fever, dengue and chikungunya, thereby inflicting mortality of nearly two million people every year worldwide (Kundsen and Slooff, 1992; Klempner et al., 2007). Besides, mosquitoes are pestiferous insects causing nuisance in human dwelling, and their bite could elicit allergic reactions such as angioedema and utricaria (Peng et al., 1999). Although many dif- ferent control methods are being practised since the ancient time, application of synthetic chemical insecticides has been found to be the effective strategy worldwide (Nauen, 2007; Morrison et al., 2008). However, the indiscriminate and arbitrary use of most of the chemical insecticides has not only resulted in development and ∗ Corresponding author. Tel.: +91 44 22202835; fax: +91 44 22301003. E-mail address: mnadhan@yahoo.com (P. Mullainadhan). 1 Present address: Department of Biotechnology, Sri Sankara Arts & Science Col- lege, Kanchipuram 631561, Tamil Nadu, India. dissemination of resistance by vector mosquitoes but also inflicted lethal effect on non-target organisms and provoked environmen- tal health concerns (Roberts and Andre, 1994; Milam et al., 2000; Nauen, 2007). These undesirable impact of chemical insecticides generated interest to find newer methods for mosquito control, especially exploration of eco-friendly biocide with potent anti- mosquito property. More than 2500 plants have been identified with insecti- cidal properties mainly expressed by their secondary metabolites against many insect pests of cotton, rice, vegetables, sugar cane, and insect vectors including mosquitoes, flies, fleas and lice (Grainge and Ahmed, 1988; Cabral et al., 1999; Mulla and Su, 1999; Isman, 2008; Mehlhorn et al., 2012). The efficacy of a wide range of botanical biocides has been frequently investigated on the devel- opmental, physiological and biochemical profiles of various species of insect pests and a few vector mosquitoes (Smith and Mitchell, 1988; Smirle et al., 1996; Laranja et al., 2003; Huang et al., 2004; Anuradha et al., 2007; Koodalingam et al., 2011; Pontual et al., 2012). In view of multiple effects, the botanical biocides can also exert adverse effects on the immune system of target insects. Indeed, the immune system interacts intimately with the func- tion of many organs within the organisms, and this system has been found to be extremely vulnerable to internal damage caused by xenobiotics (Fournier et al., 2000). Therefore, any perceptible change detectable in immune responses of insects upon exposure to botanical biocides could be used as one of the reliable biomarkers 0001-706X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.actatropica.2013.02.021