Proc. 6 th Int. Con. Biol. Sci. (Zool) Humoral response and plasma changes of Spodoptera littoralis (Lepidoptera: Noctuidae) following injection with the entomopathogenic fungi: Beauveria bassiana and Nomuraea rileyi Wesam S. Meshrif 1 , Marko Rohlfs 2 , Mohamed A. M. Hegazi 1 , Magdi G. Shehata 3 , Emad M. S. Barakat 3 and Amal I. Seif 1 1 Department of Zoology, Faculty of Science, Tanta University, Tanta, Egypt. 2 Department of Animal Ecology, J. F. Blumenbach Institute of Zoology and Anthropology, University of Goettingen, Goettingen, Germany; 3 Department of Entomology, Faculty of Science, Ain Shams University, Cairo, Egypt. ABSTRACT Carbohydrates, lipids and proteins contents as well as phenoloxidase and lysozyme activities were assessed in plasma of Spodoptera littoralis larvae injected with two virulence-different entomopathgenic fungi: Nomuraea rileyi and Beauveria bassiana. Infection was achieved by injecting 10μl of sublethal dose of blastospore suspension into the 6 th instar larvae. There was initial significant increase in plasma carbohydrates of larvae injected with the entomopathogenic fungi under investigation. However, no significant changes of the plasma carbohydrates were observed in the subsequent time intervals. Both lipid and protein contents of larvae injected with the fungi significantly decreased as compared with control insects, especially following injection with N. rileyi. Different response in plasma phenoloxidase was observed following infection with either fungus. Late significant decrease was observed after challenge with N. rileyi. The overall results indicated that S. littoralis larvae mounted a strong humoral immune response to B. bassiana, but weak response to N. rileyi. The weak humoral immune response to N. rileyi could be correlated to the marked reduction in plasma nutrients in the host thereby suggesting that the capacity of fungal pathogen to consume host nutrients might be considered one of the virulence factors. Key words: Cotton leafworm, entomopathogenic fungi, haemolymph, immunity. INTRODUCTION Human population estimate was approximately 6.5 billions in 2005 and is expected to continuously increase to 9.1 billions by mid-century (United Nations, 2004). This rapid increase coupled with changes in dietary habits towards high quality food is thought to cause more than double demands for crop production. However, land suitable for agricultural production is limited and the climate changes will add to the crisis (Tubiello et al., 2007). Therefore, crop protection plays a key role in safeguarding crop productivity against competition from weeds, animal pests and pathogens. But the global losses due to animal pests is estimated with 18% (Oerke and Dehne, 2004). Insect pests was the target for many control programs since the time of DDT invention or even before (Kogan, 1998). Due to increasing development of resistance in arthropod species in response to the use of several classes of chemical insecticides (Denholm et al., 2002), a significant attention was given to the use bio-insecticides to control insect pests (Lacey et al., 2001). The cotton leafworm, Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) is being considered as one of the most destructive pests to crops in Africa, South Europe and the middle east (Aydin and Guerkan, 2006). Many entomopathogenic fungi were found to be efficient biological agents to control this pest. Beauveria bassiana and Nomuraea rileyi are pathogenic to a number of economically important lepidopterous insects including the cotton leaf worm; they drastically affected its life-history (Meshrif et al., 2007b). Furthermore, N. rileyi was more virulent than B. bassiana against S. littoralis larvae (Meshrif et al., 2007a). Yet the underlying mechanisms affecting successful infection of S. littoralis by various entomopathogenic fungi remain elusive. Although extensive studies have been conducted on the process of cuticle penetration by entomopathogenic fungi (Charnley and Collins, 2007), interactions of entomopatognic fungi with haemolymph components remains under-explored. Insect plasma is the transport system for nutrients, hormones, and metabolic wastes, and contains elements of the immune system (Gillott, 2005). Trehalose (abundant carbohydrate) and fatty acids (lipid) represent a readily oxidizable pool of energy reserves (Thompson, 2003). Proteins function in insect immunity to detect and resist infection (Boman and Hultmark, 1987; El Chamy et al., 2010). Humoral immune response in insects is manifested by expression of antimicrobial peptides genes which are regulated by Toll and Imd pathways discovered in Drosophila (Kaisho and Akira, 2001). After infection, antimicrobial peptides are synthesized in the fat body and then released to the haemolymph (Wojda et al., 2009). Otherwise, the immune response indeed requires substantial energy to