Deborah L. Boykin

Increased Mortality of Coptotermes formosanus (Isoptera: Rhinotermitidae) Exposed to Eicosanoid Biosynthesis Inhibitors and Serratia 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.

Genomic profile of maize response to Aspergillus flavus infection

The opportunistic pathogen Aspergillus flavus infects important seed crops, including corn, peanuts, and cotton. A. flavus is capable of producing mycotoxins called aflatoxins. Aflatoxin B1, the major mycotoxin contaminant of maize, is a potent carcinogen and has been directly linked to hepatocellular carcinoma. Natural sources of maize fungal resistance exist, but efforts to increase resistance through traditional plant breeding have yielded little success. Using the maize Unigene 1-1.05 arrays, a comparison of resistant (Mp313E) and susceptible (Va35) inbred maize lines 48 hours post-A. flavus infection identified 236 genes as significant. During infection, 135 genes were up-regulated in the susceptible maize line Va35, 112 genes were up-regulated in the resistant maize line Mp313E, 12 genes were up-regulated in both lines, and 1 gene was down-regulated in both lines compared to uninfected lines. Comparisons of the biological profile responses of these maize lines revealed a striking difference in reaction to infection. These identified genes will serve as the initial step for developing molecular markers to understand this complex interaction and help with introgression of A. flavus resistance into maize hybrids.