Journal of Insect Physiology 54 (2008) 17–24 Eicosanoids mediate melanotic nodulation reactions to viral infection in larvae of the parasitic wasp, Pimpla turionellae Yonca Durmus - a , Ender Bu¨yu¨kgu¨zel a , Burcin Terzi a , Hasan Tunaz b , David Stanley c,Ã , Kemal Bu¨yu¨kgu¨zel a a Department of Biology, Faculty of Arts and Science, Karaelmas University, Zonguldak, Turkey b Department of Plant Protection, Faculty of Agriculture, Kahramanmaras - Su ¨tc - u ¨I ˙ mam University, Kahramanmaras - , Turkey c USDA/Agricultural Research Service, Biological Control of Insects Research Laboratory, 1503 S. Providence Rd., Columbia, MO 65203, USA Received 1 February 2007; received in revised form 21 March 2007; accepted 21 March 2007 Abstract Nodulation is the quantitatively predominant insect cellular immune function activated in response to bacterial, fungal and some viral infections. We posed the hypothesis that parasitoid insects express melanotic nodulation reactions to viral challenge and that eicosanoids mediate these reactions. Treating fifth-instar larvae of the ichneumonid endoparasitoid Pimpla turionellae with Bovine Herpes Simplex Virus-1 (BHSV-1) induced nodulation reactions in a challenge dose-dependent manner. Experimental larvae treated with the cyclooxygenase inhibitor, indomethacin, the lipoxygenase inhibitor, esculetin, and the phospholipase A 2 inhibitor, dexamethasone, resulted in severely impaired nodulation reactions to our standard BHSV-1 challenge dose. The immunoinhibitory influence of dexamethasone was reversed in larvae reared on culture medium amended with arachidonic acid, the fatty acid precursor of eicosanoid biosynthesis. Larvae that had been reared on media amended with indomethacin, esculetin, or dexamethasone were also compromised in their nodulation reactions to viral challenge. The influence of the orally administered pharmaceutical was expressed in a dose-dependent manner. Finally, wasp larvae reared in the presence of indomethacin and dexamethasone expressed significantly decreased levels of phenoloxidase activity in response to viral challenge. These findings draw attention to the idea that endoparasitoid insects express cellular immune reactions to viral challenge; they also support our hypothesis that eicosanoids mediate nodulation reactions to viral challenge in these highly specialized insects. r 2007 Elsevier Ltd. All rights reserved. Keywords: Parasitoid wasp; Pımpla turıonellae; Cellular immunity; Nodulation; Phenoloxidase; Eicosanoids 1. Introduction Eicosanoids are produced by enzymatic oxygenation of arachidonic acid (AA) and two other C20 polyunsaturated fatty acids. The two major groups of eicosanoids are prostaglandins and the many lipoxygenase products. Virtually all animals are thought to biosynthesize a wide range of eicosanoids, which serve in a large (but unknown) number of molecular, physiological and ecological actions (Stanley, 2000; Curtis-Prior, 2004). Among their important biological actions, eicosanoids act in several aspects of insect immunity. Two categories of insect innate immune reactions are appreciated. Humoral reactions involve induced biosynthesis of various anti-microbial peptides and proteins (Hoffmann, 2003). Cellular reactions include nodulation, encapsulation and phagocytosis (Stanley, 2006; Stanley and Miller, 2006). Miller et al. (1994) proposed that nodulation reactions to bacterial infection are mediated by eicosanoids. This eicosanoid hypothesis has been supported by reports, on over 20 insect species, from several laboratories (Stanley and Miller, 2006). Looking in more detail than nodulation, eicosanoids also mediate particular steps that lead to observable cell actions. Mandato et al. (1997) reported that ARTICLE IN PRESS www.elsevier.com/locate/jinsphys 0022-1910/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jinsphys.2007.03.019 Ã Corresponding author. Tel.: +1 875 573 5361x245; fax: +1 875 573 5364. E-mail address: stanleyd@missouri.edu (D. Stanley).