129 JBiopest, 5 (Supplementary): 129-134 (2012) 129 © JBiopest. 294 Biocidal activity of two marine green algal extracts against third instar nymph of Dysdercus cingulatus (Fab.) (Hemiptera: Pyrrhocoridae) A. Asha, J. Martin Rathi 1 , D. Patric Raja 2 and K. Sahayaraj* ABSTRACT Seaweeds are the extraordinary sustainable resources in marine ecosystem which have been used traditionally as source of food, feed and medicine. The biological effects of thallium Hexane (HE), Chloroform (CH), Methanol (ME) and Water (AQ) extract of Ulva fasciata Delile (UF) and Ulva lactuca Linnaeus (UL) were tested against Dysdercus cingulatus (Fab.) third instar nymphs at different concentrations (100, 200, 400, 600 and 800 ppm). Tested green algae caused dose dependent mortality. The ME of UF (LC 50 = 313.59 ppm) and UL (LC 50 = 399.27 ppm) shows more nymphicidal activity at 96 hrs. It is concluded that methanol extract of both UF and UL possesses nymphicidal, antiovipositional activity, reduced fecundity, hatchability, adult longevity and relative growth rate. However, more detailed studies are essential before recommending them for pest management programme. Key words: Cotton pest management, Dysdercus cingulatus, nymphicidal activity, ovipositional activity, seaweeds, Ulva fasciata, Ulva lactuca INTRODUCTION In recent years, yield of cotton has become static rather it is declining due to the infestation of insect pests and diseases. Nearly 162 species of insect pests cause low yield of cotton production. The sucking pests of cotton includes cotton stainer, jassids, aphids, white flies and thrips (Uthamasamy et al ., 2004).The red cotton bug or cotton stainer Dysdercus cingulatus (Fab.) (Hemiptera: Pyrrhocoridae) is considered as a serious pest of cotton (Waterhouse, 1998; Tanu Sharma et al ., 2010). It infests the cotton from young stage still harvest. This pest causes serious damage by sucking the developing cotton bolls and ripe cotton seeds and transmitting fungi that develops in the immature lint and seeds (Fuseini and Kumar, 1975; Yasuda, 1992). Dysdercus cingulatus is difficult to control by insecticidal application because they are highly mobile and have many alternative wild hosts belonging to Malvaceae (Iwata, 1975; Kohno and Ngan, 2004).The marine algae are the renewable living resources which are rich source of structurally important novel and biologically active metabolites. Marine algae have been shown to have bactericidal (Febles et al ., 1995; Del et al ., 2001; Ely et al ., 2004 and Cordeiro et al ., 2006), fungicidal (Rajesh et al ., 2011) and insecticidal activities (Biju et al., 2004; Cetin et al., 2010; Sahayaraj and Kalidas, 2011; Sahayaraj and Mary Jeeva, 2012). Further more, seaweed extracts offer a novel approach to pest management (Manilal et al ., 2009; Rajesh et al ., 2011; Sahayaraj and Kalidas, 2011; Sahayaraj and Mary Jeeva, 2012).Ulva fasciata Delile is a marine macroalga, which grows abundantly in the coastal waters of South India.Ulva fasciata and Ulva lactuca have been reported to possess antioxidant and antibacterial properties (Beach et al., 1995; Rouxel et al ., 2001). The previous reports do not show much information regarding insecticidal activity of seaweed extracts against D. cingulatus. The present reports deals with the bioefficacy of U. fasciata and U. lactuca on biological insecticidal, fecundity, hatchability, adult longevity and relative growth rate (RGR) of D. cingulatus. MATERIALS AND METHODS Collection, extraction and preparation of seaweed extract The algae Ulva fasciata and Ulva lactuca were collected by hand picking method from the submerged marine rocks at Idinthakarai (N 08Ú10’ 32.3"; E 077’ 44’31.3") Kuthenkuzhi (N 08’10’32.3"; E 077’46’58.4") and Tuticorin (N 08’46’32.1"; E 078’11’56.5"), Tamil Nadu, India from June to December, 2010. The seaweeds were washed thoroughly thrice with tap water and once with sterile distilled water to remove salt, sand and epiphytes. Shade dried for two weeks and partially powered using domestic blender (Preethi XL-7, Maya Appliances (P) Ltd. Madras). For extraction, 500 gm of powdered algal material was extracted by Soxhlation method using polar (methanol- ME, water- AQ) and non-polar (chloroform- CH, hexane- HE) Biocidal activity of marine algae