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Abstract
Chitinolytic enzymes are responsible for hydrolysis of chitin polymers. Degradation of chitinous structures is carried out by a two-component chitinolytic enzyme system (endo- and exo-chitinases). Insecticidal efficacy by inhibition of chitinolytic enzymes remains an area of potential insecticide discovery. This study evaluated the toxicity, palatability, and effects on chitinolytic enzyme activities of pentoxifylline and psammaplin A (Family 18 chitinase inhibitors) on eastern subterranean termites.
Both chitinase inhibitors were shown to be toxic to R. flavipes . Concentration-dependent toxicity occurred within the psammaplin A treatments and throughout the range of 3.5 - 28 micrograms/milliliter pentoxifylline treatments. Within pentoxifylline treatments, intermediary treatment concentrations displayed the maximal toxicity.
Generally, psammaplin A displayed higher termiticidal activity than pentoxifylline. However, psammaplin A deterred feeding at the highest concentrations tested, while pentoxifylline treatments generally did not deter feeding. Mortality resulting from psammaplin A was shown to be dose dependent, while pentoxifylline dependent mortality more closely correlated with amount of diet consumed.
In a whole termite, numerous (insect and non-insect) endo-chitinase isoforms exist. Pentoxifylline treatment 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 affected both in vivo endo- and exo-chitinase enzyme activities. In vitro, Psammaplin A treatment affects endo-chitinase activities (in a concentration-dependent manner), while having slight effects on exo-chitinase enzyme activities. However, in vivo, psammaplin A treatment affects both endo- and exo-chitinase enzyme activities (with concentration-dependent endo-chitinase inhibition observed).
This study provided the first report on toxicity of chitinolytic enzyme inhibitors against eastern subterranean termites. These results indicate the potential of novel chitinase inhibitors, either naturally (psammaplin A) or synthetically produced (pentoxifylline), when used at non-deterring concentrations to be effective active ingredients for a termite baiting program.
