Increased mortality of Coptotermes formosanus (Isoptera : Rhinotermitidae)exposed to eicosanoid biosynthesis inhibitors and Serratia marcescens (Eubacteriales : Enterobacteriaceae)

The biological control of termites may be facilitated if their highly evolv ed immune systems can be suppressed. Eicosanoids are C20 polyunsaturated ac ids that are of widespread biochemical importance, including their role in protecting insects from bacterial infection. In laboratory experiments, the eicosanoid biosynthesis inhibitors dexamethasone, ibuprofen, and ibuprofen sodium salt were each provided along with a red-pigmented isolate of Serra tia marcescens Bizio, a bacterial pathogen, to the Formosan subterranean te rmite, Coptotermes formosanus Shiraki, by means of treated filter paper. Th e increased mortality that resulted with dexamethasone and ibuprofen suppor ted, but alone was insufficient to prove, the hypothesis that the termites' immune systems were suppressed by these compounds, making the insects more vulnerable to infection by S. marcescens. This effect on mortality was not ed only at 3.4 X 10(10) colony-forming units per milliliter, a high treatme nt level. A significant amount of the infection and subsequent mortality ma y have resulted from direct contact with the bacterium and die remainder fr om its ingestion. Water-soluble ibuprofen sodium salt demonstrated a protec tive effect that was unexpected in light of die increased termite mortality observed with the relatively water insoluble, free acid form.