Timothy J. Husen

Delayed Toxicity of Two Chitinolytic Enzyme Inhibitors (Psammaplin A and Pentoxifylline) Against Eastern Subterranean Termites (Isoptera: Rhinotermitidae)

ABSTRACT By using a no-choice feeding bioassay, delayed toxicity and concentration-dependent mortality of two chitinolytic enzyme inhibitors, pentoxifylline and psammaplin A, were evaluated by determining LT50, LT90, and LT99 (lethal time) against the economically important eastern subterranean termite, Reticulitermes flavipes (Kollar). Pentoxifylline- and psammaplin A-incorporated diets (filter paper) were assayed at 0.01, 0.02, 0.04, 0.08, and 0.21% and 0.0375, 0.075, 0.15, and 0.3% active ingredient (wt:wt), respectively. Acetone-only treated filter paper served as diet for the control treatments. Termite workers were allowed to feed on diet until 100% test population mortality occurred (80–95 d). Both chitinase inhibitors were shown to be toxic to R. flavipes. Concentrationdependent 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. However, mortality in response to psammaplin A treatments lacked concentration-dependent toxicity. Treatment with 0.3% psammaplin A produced an LT50 of 21.3 d. Mortality in response to lower psammaplin A treatments displayed no concentration-dependent trends. This study provides the first report on delayed toxicity of chitinolytic enzyme inhibitors against eastern subterranean termites (order Isoptera) and toxicological data on pentoxifylline and psammaplin A over a range of concentrations.

An Evaluation of Chitinase Inhibitors, Psammaplin A and Pentoxifylline, Treated Diets against the Eastern Subterranean Termite (Isoptera: Rhinotermitidae)

Abstract Psammaplin A and pentoxifylline, two chitinolytic enzyme inhibitors, were evaluated for their palatability, feeding deterrence, consumption, and subsequent mortality against the eastern subterranean termite, Reticulitermes flavipes (Kollar). Psammaplin A and pentoxifylline were incorporated into filter paper diets at 0.0375, 0.075, 0.15, and 0.3%, and 0.01, 0.02, 0.04, 0.08, and 0.21% active ingredient (w/w), respectively. The treated filter papers served as food source or bait for termite workers used in this study. No-choice and two-choice feeding bioassays assessed bait consumption, palatability, repellency, and biological activity over a period of 1 - 5 wk (no-choice assay) and 3 - 5 wk (two-choice assay) of feeding. Neither psammaplin A nor pentoxifylline treatment repelled eastern subterranean termite diet consumption (in both nochoice and two-choice feeding arenas) as feeding commenced on both diet types within 48 h. In no-choice feeding tests, diet consumption was significantly decreased in termites fed 0.3% (2 - 5 wk) and 0.15% (4 - 5 wk) psammaplin A treated diet. Pentoxifylline treatment decreased diet consumption at 0.21% (3 wk). Consumption ratio trends suggest increased diet consumption rates by survivors feeding on chitinase inhibitor treated diet. In two-choice tests, termites consumed almost equal amount of diet treated with psammaplin A or pentoxifylline and untreated diet (with the exception of diet treated with 0.3% psammaplin A). Under no-choice bioassays, termite mortality from all concentrations of both chitinase inhibitor treated diets was significantly greater than that from untreated diet. Biological activity of psammaplin A and pentoxifylline treated diets in 2-choice feeding arenas was reduced by greater than 50% in comparison with no-choice feeding arenas. These results indicate the novel potential of chitinase inhibitors as effective active ingredients for a termite baiting program.

Effect of Pentoxifylline on Chitinolytic Enzyme Activity in the Eastern Subterranean Termite (Isoptera: Rhinotermitidae)

Abstract  A two-molecule chitinolytic enzyme system (endo- and exo-chitinase) hydrolyzes and degrades the chitin polymers. Therefore, it is imperative to discover novel compounds for inhibiting chitinolytic enzymes to prevent insect growth. This research examined the effect of pentoxifylline (a dimethylxanthine chitinase inhibitor) on inhibition of endo- and exo-chitinolytic enzyme activities in eastern subterranean termite, Reticulitermes flavipes (Kollar). Enzyme activities were compared with amounts of treated diet consumed by termites and percent mortality observed over time. Pentoxifylline affected in vitro endo-chitinase activity in a concentration-dependent manner, while having minimal to no effect on in vitro exo-chitinase enzyme activity. However, pentoxifylline treatment affected in vivo endo- and exo-chitinase enzyme activity and caused measurable termite mortality. Moreover, pentoxifylline concentrations did not deter the amount of diet consumed by termites, thereby suggesting that it is palatable. The results of this study support further exploration into termiticidal activity and potential use of pentoxifylline for termite control.