Increased Mortality ofCoptotermes formosanus(Isoptera: Rhinotermitidae) Exposed to Eicosanoid Biosynthesis Inhibitors andSerratia marcescens(Eubacteriales: Enterobacteriaceae)

Abstract

The biological control of termites may be facilitated if their highly evolved immune systems can be suppressed. Eicosanoids are C20 polyunsaturated acids 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 Serratia marcescens Bizio, a bacterial pathogen, to the Formosan subterranean termite, Coptotermes formosanus Shiraki, by means of treated filter paper. The increased mortality that resulted with dexamethasone and ibuprofen supported, 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 noted only at 3.4 × 1010 colony-forming units per milliliter, a high treatment level. A significant amount of the infection and subsequent mortality may have resulted from direct contact with the bacterium and the remainder from its ingestion. Water-soluble ibuprofen sodium salt demonstrated a protective effect that was unexpected in light of the increased termite mortality observed with the relatively water insoluble, free acid form.