Of all insects, termites represent one of the greatest threats to wood and timber. Termites cause damage all over the world, especially in the tropics. The tropical/sub-tropical climate of Taiwan island, with warm and wet weather most of the time, is an ideal environment for termites.
Termites can be divided into six genera, with about 2,200 species. Of these, 15 are native to Taiwan. In the USA there are 43 species, but the most destructive is the Formosan subterranean termite. In 1986 alone, this species was responsible for 2 billion dollars of damage in the USA.
Anti-termite measures fall into three general categories: biological, physical, and chemical. Using chemical repellents is effective, but the chemicals pose a threat to humans who come into contact with them. They also pollute the environment, so in these environmentally-conscious times, a more natural solution to the problem is wanted. Researchers in many countries are therefore looking seriously at using essential oils or plant extracts instead.
TFRI has conducted research into essential oils as anti-termite treatments, and has obtained some positive results:
(1) Melia azedarach : termites were tested on sawdust impregnated with a 10% solution of four different chinaberry extracts, from the fruit, bark, leaves, and seeds. After 15 days, all termites in fruit, bark and leaves groups were dead, as were 65% of those in the seed group.
(2) Litsea cubeba: filter paper and sawdust tests were carried out with essential oils from the leaves, flowers, fruit and bark of Litsea cubeba. The best results came from the bark oil, followed by leaf, fruit and flower oils. In practical terms, the leaves are the easiest to use.
(3) Cinnamon: essential oil from the leaves of the Cinnamomum zeylanicum proved most effective; followed by mixed essential oils from the Cinnamomum osmophloeum and Cinnamomum zeylanicum ; and oils from Cinnamomum osmophloeum leaves were least powerful. In a filter paper test, all termites were killed within 24 hours by the following 2% solutions: essential oils from Cinnamomum zeylanicum leaves; mixed Cinnamomum zeylanicum ; synthetic eugenol.
(4) Eucalyptus: there is great variation among the oils of different eucalyptus species. The best results were recorded with essential oils from the leaves of Eucalytus grandis and Eucalytus globulus. All termites died within 24 hours in filter paper test with a 2% solution. Eucalytus citriodor and Eucalyptus urophylla were less effective (50% and 40% death rate, respectively); Eucalytus umbellata (20%) and Eucalytus camalculensis (14%) still less so; and the worst results occurred with oils from Eucalytus robusta (0%).
Pesticides based on essential oils are not harmful to environment and to people as conventional chemical pesticides. Furthermore, essential oil pesticides represent a commercial opportunity for forest products, and a new way of realizing the value of Taiwan's forests.