Eicosanoids mediate nodulation reactions to a mollicute bacterium in larvae of the blowfly, Chrysomya megacephala

Nodulation is the temporally and quantitatively most important cellular defense response to bacterial, fungal and some viral infections in insects. We tested the hypothesis that prostaglandins and other eicosanoids are responsible for mediating nodulation reactions to bacterial infection in larvae of the blowfly Chrysomya megacephala. Third-instar larvae treated with Ureaplasma urealyticum formed nodules in a challenge dose-dependent manner. Nodulation was evoked shortly after injection and reached a maximum of approximately 25 nodules/larva within 8 h. Larvae treated with the glucocorticoid, dexamethasone and the cyclooxygenase inhibitors, indomethacin and piroxicam were impaired in their ability to form nodules following U. urealyticum infection. The number of nodules decreased with increasing doses of piroxicam. Contrarily, treating larvae with the lipooxygenase inhibitor, esculetin, and the dual cyclooxygenase/lipooxygenase inhibitor, phenidone did not influence nodulation reactions to infection. Supplying dexamethasone-treated larvae with the eicosanoid precursor, arachidonic acid, reversed the inhibitory effect of dexamethasone on nodulation. We infer from these results that eicosanoids mediate nodulation reactions to infection of a bacterial species that lacks cell walls in larvae of the blowfly, C. megacephala.