Natural repellant could save endangered tree

Spanish cedar trees are found primarily in Central America, the Caribbean, West Africa and Asia and are harvested to make furniture

September 7, 1999
Web posted at: 2:07 p.m. EDT (1807 GMT)

The leaves of an over-harvested tropical cedar tree may contain a naturally occurring insect repellant that will make plantation farming feasible, thereby reducing the threats posed by deforestation, according to a team of British researchers.

The Spanish cedar is found primarily in Central America, the Caribbean, West Africa and Asia. Its hardwood, mahogany-like properties make it a popular wood for use in buildings and furniture. As a result they are being severely over-harvested in the wild, necessitating the need for plantations.

The success of plantations, though, is threatened by the invasion of insects such as mahogany webworms, shoot-borers and weevils. If plantation-raised timber production does not succeed, however, scientists are afraid that endangered primary forests will suffer.

So a team of researchers based at the Royal Botanic Gardens, Kew, the University of Oxford, and the Natural Resources Institute at the University of Greenwich, all in Great Britain, set out to determine if the leaves of the Spanish cedar offered any protection from insects. They found that some of the leaves contained substances — known as limonoids — that the insects avoided.

"Seedlings would be selected for the presence of these compounds at high

Seedlings with high concentrations of insect repelling compounds will be selected for plantations

concentrations before planting out in plantations," said Phil Stevenson, a natural produce chemist at the Jodrell Laboratory of the Royal Botanic Gardens in Kew, England.

"We hope our findings will help in the protection of endangered primary forests in the tropics by promoting economically viable alternatives for timber production," he added in a statement.

Foresters could establish plantations on deforested land or on farmland where Spanish cedar was deemed more profitable than other crops. "The farmland would have been cleared from forests in the first place anyway," said Stevenson.

While the researchers will look for Spanish cedar seedlings that have high concentrations of limonoids and create clones from those trees, they have no plans to genetically engineer trees or to produce an insecticide with synthetic limonoids.

"Super-protection wants to be avoided in most uses of natural resistance because super-protection will promote the rapid evolution of super bugs — i.e. those which can tolerate the plant chemicals," said Stevenson.

An article on this research will be published in the American Chemical Society's Sept. 24 issue of the Journal of Natural Products.

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