EICOSANOIDS MEDIATE NODULATION RESPONSES TO BACTERIAL-INFECTIONS IN LARVAE OF THE TENEBRIONID BEETLE, ZOPHOBAS-ATRATUS

Nodulation is the temporally and quantitatively predominant cellular d efense response to bacterial infection in insects and other invertebra tes, Inhibition of eicosanoid biosynthesis in larvae of the tenebrioni d beetle, Zophobas atratus, immediately prior to intrahemocoelic injec tions with heat killed preparations of the bacterium, Serratia marcesc ens, strongly reduced the nodulation response, Separate treatments wit h specific inhibitors of phospholipase A2(,) cyclooxygenase, and lipox ygenase reduced nodulation, supporting the view that nodule formation is a complex process involving both cyclooxygenase and lipoxygenase pr oducts, The inhibitory effects of the phospholipase A(2) inhibitor, de xamethasone, on nodulation were apparent 1 h after infection, and the effects increased, relative to controls, over 24 h, The dexamethasone effects were expressed in a dose-dependent manner, and they were rever sed by treating bacteria injected insects with the eicosanoid-precurso r polyunsaturated fatty acid, arachidonic acid (C20:4n-6), Treatments with the saturated fatty acid, 16:0, which is not an eicosanoid precur sor, did not reverse the dexamethasone effects on nodulation, The inse cts contain low levels of three eicosanoid precursor polyunsaturated f atty acids in six different tissues, and fat body preparations are com petent to produce both cyclooxygenase and lipoxygenase products, These findings strongly support the identification of nodulation as a speci fic insect cellular defense mechanism that is mediated by eicosanoids.