Dutch elm fungus turns tree into lure.

The fungus that causes Dutch elm disease makes an infected tree strengthen its odors, attracting beetles that carry the fungus on to the next tree, researchers have found.

The killer fungus somehow hitchhiked to North America from Europe during the 1930s and has been wiping out elm trees ever since. A particularly virulent form, Ophiostoma novo-ulmi, appeared in the 1960s.

Gerhard Gries of Simon Fraser University in Burnaby, British Columbia, and his colleagues extracted volatile compounds from the sawdust of trees infected with O. novo-ulmi. Among these chemicals, they identified four terpene compounds that could elicit neural responses in the antennae of the elm bark beetle (Hylurgopinus 7utfipes), which is native to North America and is one of the insects that gives the fungus a lift from tree to tree.

Because the researchers found the alluring cocktail in infected wood but not in patches of fungus grown on a lab medium, they argue that the tree, not the fungus, produces the compounds. When placed in traps, the quartet of terpenes indeed attracted the beetles, but only if the cocktail had all four ingredients in their natural proportions. Gries and his colleagues report their findings in an upcoming Proceedings of the Royal Society B. --S.M.