Lara Maistrello and Gregg Henderson, LSU Ag. Center, Dept of Entomology, Baton Rouge, LA
Vetiver grass (Vetiveria zizanioides) is an Indian native plant whose domesticated type is cultivated worldwide in tropical and subtropical regions for its efficacy against soil erosion and for the commercial importance of its oil, extracted from the roots. People may be familiar with this plant since many soaps, perfumes and after-shave include vetiver oil as active ingredient. Moreover, nootkatone, one of the 300 components of vetiver oil, is used to aromatize drinks with its distinctive grapefruit flavor. What people ignore is that the same pleasant aromas ...can be our next, natural remedy against those exotic, tiny, whitish bugs devouring houses and any kind of wooden structures, and represent the major insect pests in the southern United States.
As part of our research on natural product efficacy against Formosan subterranean termites, we are performing experiments to test the response of Coptotermes formosanus to substrates and food sources treated with vetiver oil and some of its components, like nootkatone. The results show that these compounds are able to disrupt termite behavior and physiology as a consequence of direct physical contact, ingestion, or exposure to the vapors. In the presence of this compounds termites show a lingering behavior, remaining on the surface all clumped together, unable to organize themselves to reach potential food sources through tunneling activity or building shelter tubes. Moreover, ingestion of wood treated with vetiver oil or nootkatone causes the progressive death of the protozoa living inside the termite gut. Killing these symbiont microorganisms, on which these insects rely on for the digestion of their wooden food, would mean a progressive decline of a termite colony through starvation, until total extinction.
These pictures show the results of an experiment in which Formosan subterranean termites had to tunnel through sand in order to reach the food source, a wood slice which had been treated with 1% solutions of vetiver oil (V1) or nootkatone (N1) or Tim-Bor ®, a commonly used pesticide to prevent wood damaging by termites (T1).
The effects on the protozoa population (average number of protozoa per termite gut) show that wood treated with vetiver oil or nootkatone was as effective as the one treated with Tim-Bor ®, inducing a high, significant reduction in the number of these microorganisms, indispensable to termites.