In laboratory choice bioassays, Reticulitermes flavipes (Kollar) and Coptotermes formosanus Shiraki were offered a tunneling soil consisting of boric acid (BA) mixed with sterilized soil at concentrations of 0.05, 0.25, 0.50, 1.00, 2.00, or 4.00 percent AI (wt:wt). Termites could choose to remain in their main nest that contained non-treated artificial substrate and adequate food, or tunnel through BA-treated soil in an attached foraging tube to reach a satellite nest that also contained non-treated artificial substrate and additional food. Gut protozoa populations were determined after 12 weeks. Termite tunneling through BA -treated soil resulted in moderate reduction to complete loss of symbiotic gut protozoa in both termite species as BA increased to the greatest concentration. Reductions in protozoa were most noticeable in the 2.00 and 4.00 percent BA concentrations. Boric acid was not repellent and termites removed BA-treated soil from foraging tubes and deposited it in main and satellite nests. Generally, at BA concentrations of 1.00-2.00% or less in soil, termite gut protozoa populations did not appear to be dose dependent. The four primary protozoa genera in R. flavipes and the three primary protozoa genera in C. formosanus were all detrimentally affected by exposure to BA. Overall, BA mixed in soil caused significant loss of protozoa that was very detrimental to both termite species.

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