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Eicosanoids act in nodulation reactions to the bacterium Serratia marcescens in the Hemipteran pest Eurygaster integriceps

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In insects, nodulation is the first step in cellular defense reactions to bacterial, fungal, and some viral infections. The hypothesis was posed that the hemipteran pest E. integriceps produces melantoic nodulation reactions to bacterial challenge and that eicosanoids mediate these reactions. Treating the adult of E. integriceps with Serratia marcescens induced nodulation reactions in a challenge dose-dependent manner. Injecting the adult E. integriceps with eicosanoid biosynthesis inhibitors, immediately before intrahemocoelic injections of the bacterium Serratia marcescens, sharply reduced the nodulation response to bacterial challenges. Separate treatments with specific inhibitors including dexamethasone (a phospholipase A2 inhibitor), indomethacin, naproxen, ibuprofen, piroxicam (cyclooxygenase inhibitors), esculetin (a lipoxygenase inhibitor), and phenidone (dual cyclooxgenase/lipoxygenase inhibitor) also impaired the ability of E. integriceps to form nodules in reaction to bacterial challenge. The inhibitory influence of ibuprofen was apparent within 30 min after infection, and nodulation was significantly reduced, relative to control insects, over the following 4 h. Increasing ibuprofen dosages were associated with decreasing nodulation activity. The dexamethasone effects were reversed by treating bacteria-injected insects with the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid. These findings support the hypothesis that eicosanoids also act in nodulation reactions to bacterial infections in the hemipteran pest E. integriceps.

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