The response and recovery of the Formosan subterranean termite (Coptotermes formosanus Shiraki) from sublethal boron exposures

Abstract

Controlling the Formosan subterranean termite, a cosmopolitan pest and the most structurally damaging pest in the state of Hawaii, is an important priority for homeowners and commercial builders alike. Boron-treated lumber is often part of an effective integrated pest management (IPM) strategy, owing to its effect of reducing attack by subterranean termites and preventing wood decay due to fungi and bacteria. Termites from field colonies maintained in Honolulu were collected and exposed to one of four composite boards: zinc borate (ZB)/disodium octaborate tetrahydrate (DOT) (boric acid equivalent or BAE 0.75%), anhydrous boric acid (B2O3) (BAE 0.75%), or an untreated composite board control; after 5 days the wood pieces were replaced with untreated composite boards. The effect of 5 days of boron exposure was examined by comparing the wet weight of termites, wood consumption, survival, and termite boron content. The analyses at both 5 and 10 days revealed significantly more boron in the termites exposed to treated timber than those not exposed, and decreased weight in those termites exposed to borates. The general trend was for the ZB treatment to have less of an effect on the termites than the DOT treatment, while were both less harmful than boric acid in these experiments. The boron content of the exposed termites declined by 66–74% after 5 days of feeding on untreated wood, indicating that termites can excrete or metabolize ingested boron over time. This ability to recover from sublethal exposure to boron may explain the gradual avoidance of borate-treated wood noted by other authors, and has implications for the inclusion of borate-treated timber in an IPM programs for preventing infestation by subterranean termites.