INTRODUCTION Biological invasions are a great threat to human interests, often affecting ecosystem functionality, biodiversity and human health (Aragon et al., 2010). Increased international trade has caused the rapid movement of many organisms, especially aquatic organisms including molluscs, from one location to another (McNeely, 2001). Apple snails, Pomacea spp., natives of South America were introduced in many countries, primarily for food or aquarium trade, are among the most invasive freshwater molluscs (Cowie et al., 2006; Rawlings et al., 2007; Hayes et al., 2008; EFSA, 2012). They have caused substantial economic losses to rice in many countries of the world especially in Southeast Asia (Nghiem et al., 2013). Besides rice, they also caused substantial damage to taro, water spinach, water chestnut and lotus (Carlsson, 2006). Due to the ever confounding identification of Pomacea canaliculata and Pomacea maculata (P. insularum and P. gigas synominized with it), initially it was assumed that only P. canaliculata was introduced to Southeast Asia (Cowie et al., 2006; Hayes et al., 2012). However, later investigations and genetic studies also confirmed the introduction of P. maculata in the region (Rawlings et al., 2007; Hayes et al., 2008; Hayes et al., 2012). The invasiveness of Pomacea spp. is based on their unique morphological and physiological characteristics such as high reproductive potential with rapid growth, polyphagous feeding habits, amphibious respiration and aestivating or hibernating potential (Cowie, 2002; Estebenet and Martin, 2002). All of these characteristics help them to survive under adverse environmental conditions and reproduce aggressively. In their native habitats, they caused only minor economic losses (Cazzaniga, 2006), but heavy economic losses are incurred in their introduced range, especially Southeast Asia, China, Japan and Hawaii (Horgan et al., 2014; Nghiem et al., 2013). The losses caused by the introduced apple snails to rice in three countries of Southeast Asia, viz. Philippines, Thailand and Vietnam, are estimated up to US$ 2.138 billion per annum (Nghiem et al., 2013). They are also vectors of parasitic Angiostrongylus nematodes and cause infection of rice workers through cuts on their feet from the sharp edges of shells killed by pesticides (Horgan et al., 2014; Nghiem et al., 2013). Moreover, they also deteriorate many aquatic ecosystems to turn them into turbid and phyto-plankton dominated ones (Carlsson, 2006). Because of these impacts of Pomacea spp., one species, P. canaliculata, is included among “100 of the World’s Worst Invasive Alien Species” (Lowe et al., 2000). Although many studies have been conducted recently on the biology of P. canaliculata (e.g. Wu et al., 2011; Zhao et al., 2012; Seuffert and Martín, 2013; Yoshida et al., 2013), no significant studies have been conducted on the life cycle and biology of P. maculata. Moreover, no life cycle study of P. Pak. J. Agri. Sci., Vol. 52(4), 1075-1079; 2015 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 http://www.pakjas.com.pk COMPARATIVE LIFE CYCLE STUDIES OF Pomacea maculata AND Pomacea canaliculata ON RICE (Oryza sativa) A.G. Arfan 1,2 , R. Muhamad 1,* , D. Omar 1 , A.A. Nor Azwady 3 and G. Manjeri 1 1 Department of Plant Protection, Faculty of Agriculture, Universiti Putra Malaysia 43400 Serdang, Selangor, Malaysia; 2 Department of Entomology, Faculty of Crop Protection, Sindh Agriculture University Tandojam, Sindh, Pakistan; 3 Department of Biology, Faculty of Science, University Putra Malaysia 43400 Serdang, Selangor, Malaysia. * Corresponding author’s e-mail: rita@upm.edu.my Apple snails, P. canaliculata and P. maculata are the two most successful invaders of many macrophytes especially rice in many countries of the world particularly Southeast Asia. Many studies have been conducted on ecology and management of P. canaliculata but little is known about the life cycle of P. maculata especially on rice. Therefore, comparative life cycle studies of P. maculata and P. canaliculata were conducted on rice. Results suggested that P. canaliculata showed significantly higher growth than P. maculata and matured during the 27 th week of development, whereas the latter matured during the 32 nd week. At maturity, no difference was recorded between two species for shell length and width. However, individuals of both species started consuming rice during the 4 th week of the development. Shell length and width of both species were highly correlated with each other during the entire growth. Egg diameter was significantly higher in P. canaliculata than P. maculata, however, no significant difference was observed in the number of eggs, hatching period and rate for the two species. The results obtained can be utilized for the rearing technique of Pomacea spp. on rice to maintain cultures of different stages to study their unique features contributing to their successful invasion, and suggest appropriate management strategies to reduce their damage and spread. Keywords: Pomacea canaliculata, Pomacea maculata, apple snails, life cycle, rearing technique