This invention is a modified yeast that can be fed to termites to produce and express peptides that destroy the protozoa responsible for wood digestion in the termites’ guts. The demise of these protozoa results in the death of the termites. The time required for the yeast to kill the termites is long enough to allow transfer of the yeast among colony mates. The peptide products of the modified yeast are very specific for the wood digesting protozoa and are effective in small amounts.