Archives of Insect Biochemistry and Physiology 41:225–232 (1999) © 1999 Wiley-Liss, Inc. Prostaglandin Production in Response to a Bacterial Infection in True Armyworm Larvae Russell A. Jurenka, 1 * Venkat K. Pedibhotla, 1 and David W. Stanley 2 1 Department of Entomology, Iowa State University, Ames 2 Department of Entomology, University of Nebraska, Lincoln Prostaglandin levels were determined by fluorometric HPLC analysis of hemolymph collected from larvae of the true army- worm, Pseudaletia unipuncta, that had been injected with bacte- ria. Prostaglandins were extracted and derivatized with the fluorogenic compound 9-anthryldiazomethane and detected by fluorescence-HPLC. One of the prostaglandins produced was iden- tified as prostaglandin F 2a based on HPLC retention time. The chemical identity of prostaglandin F 2a was confirmed by isola- tion and derivatization followed by gas chromatography mass spectrometry analysis. Larvae injected with heat-killed bacteria, Serratia marcescens, produced about 4 times as much prostag- landin F 2a as larvae injected with saline. In a separate experi- ment, larvae injected with bacteria and the prostaglandin precursor arachidonic acid produced still higher levels of pros- taglandin F 2a . The production of prostaglandin was inhibited with phenidone, a dual cyclooxygenase and lipoxygenase inhibitor. These data indicate that bacterial injections stimulate increased eicosanoid biosynthesis in true armyworms, particularly biosyn- thesis of prostaglandin F 2a . Our findings add considerable sup- port to the hypothesis that eicosanoids mediate insect cellular immune reactions to bacterial infections. Arch. Insect Biochem. Physiol. 41:225–232, 1999. © 1999 Wiley-Liss, Inc. Key words: ADAM; fluorescence; Pseudaletia unipuncta; insect immunity; eicosanoid; arachidonic acid Abreviations used: ADAM = 9-anthryldiazomethane; GC = gas chromatography; HPLC = high pressure liquid chroma- toraphy; MS = mass spectrometry; PG = prostaglandin. Contract grant sponsor: Agricultural Research Division, UNL; Contract grant sponsor: Hatch Act; Contract grant sponsor: State of Iowa funds. *Correspondence to: Russell A. Jurenka, Department of En- tomology, Iowa State University. 411 Science II, Ames, IA 50011-3222. E-mail: rjurenka@iastate.edu Received 15 February 1999; accepted 7 April 1999 INTRODUCTION Prostaglandins (PGs) are oxygenated me- tabolites of arachidonic acid and two other poly- unsaturated fatty acids, eicosatrienoic and eicosapentaenoic acids. Although PGs are most widely appreciated with respect to their actions in mammals and other vertebrates, there is in- creasing interest in the significance of these compounds in invertebrates. PGs act in repro- duction, immunity, ion transport, and ecology of many, perhaps all, invertebrate phyla (Stanley- Samuelson, 1994a,b; Stanley and Howard, 1998;