Turkish Journal of Agriculture and Forestry




Injecting larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), with eicosanoid biosynthesis inhibitor, phenidone (104 µg larva^{-1}), immediately prior to intrahemocoelic injections of the fungus Beauveria bassiana (Bals.) Vuill. (Deuteromycota: Hyphomycetes) (isolate No: HRI-215: 10 µg larva^{-1} from 2 x 106 blastospores ml^{-1}), sharply reduced (about 75 %) the nodulation reaction to the fungal challenges. Separate treatments with specific inhibitors of the major enzymes involved in eicosanoid biosynthesis, including phospholipase A_2 (PLA_2), cyclooxygenase, and lipoxygenase, reduced nodulation reactions to fungal infections. These findings support the view that nodule formation is a complex process involving lipoxygenase and cyclooxygenase products. The inhibitory influence of phenidone, the dual cyclooxygenase and lipoxygenase inhibitor, was apparent within each time. Phenidone-treated larvae formed about 14 nodules/insect at 0.5 h post injection (hpi), which increased to 54 at 8 hpi, whereas the ethanol-treated control larvae produced significantly more nodules at each time, from 49 nodules at 0.5 hpi to 147 at 8 hpi. The inhibitory effect of dexamethasone on nodulation was reversed by treating fungus-injected insects with the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid. These findings support our hypothesis that eicosanoids mediate insect cellular immune reactions to fungal infections in L. decemlineata.

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