Evaluation of pentoxifylline, a chitinase inhibitor, as a subterranean termite bait active ingredient

Pentoxifylline, a chitinolytic enzyme inhibitor, was evaluated for its palatability/consumption and its delayed toxicity/concentration dependent mortality against the eastern subterranean termite, Reticulitermes flavipes (Kollar). Pentoxifylline was incorporated into filter paper diets at 0.01, 0.02, 0.04, 0.08, and 0.21% active ingredient (w/w).  No-choice and two-choice feeding bioassays examined biological activity and palatability/repellency over a period of one-to-five weeks (wk) (no-choice assay) and three-to-five wk (two-choice assay) of feeding  Using a no-choice feeding bioassay, delayed toxicity and concentration dependent mortality of pentoxifylline were evaluated by determining LT₅₀, LT₉₀, and LT₉₉ (lethal time).  Termite workers were allowed to feed on diet until 100% treated test population mortality occurred (80-95 d).    In no-choice and two-choice feeding tests, pentoxifylline treatments generally did not deter feeding with the exception of the highest concentration tested under no-choice feeding conditions.  Pentoxifylline dependent mortality closely correlated with amount of diet consumed.  Pentoxifylline was shown to be toxic to R. flavipes.  Concentration-dependent toxicity occurred within the pentoxifylline treatments over the range of 0.01-0.08% with 0.08% treatments producing an LT₅₀ of 32.2 d.  These results provide the first report on delayed toxicity of a chitinolytic enzyme inhibitor (pentoxifylline) against eastern subterranean termites (Order:  Isoptera) and indicate the novel potential of chitinase inhibitors as effective active ingredients for a termite baiting program.