A new pest-management tool could come from sex-specific pheromone laid on trees by the female Asian longhorned beetle, which is considered a pest precisely because it leads to the death of hardwood trees, according to scientists.
The news is welcome by forest management teams across the US, where the Asian longhorned beetle has led to the destruction of a significant number of trees by boring holes in the tree to lay eggs. Enough holes bored into the trunk of a tree can lead to a destruction of its structural integrity, cauing it to die or resulting it its removal by forest managers.
"Tens of thousands of hardwood trees, mostly maples, have been cut down and destroyed in New York, Ohio and Massachusetts because of the Asian longhorned beetle," said Kelli Hoover, a professor of entomology at Penn State University. "We discovered a pheromone produced by females of this species that could be used to manage the pest."
As they crawl along trees, female Asian longhorned beetles leave behind a chemical trail that their male counterparts do not.
These chemical trails consist of four major components, but their ratios and amounts change depending on the insect's age and whether the female beetle is a virgin or mated.
"We found that virgin females do not begin to produce a sufficient amount of the correct pheromone blend -- that is, the correct ratios of the four chemicals to each other -- until they are about 20 days old, which corresponds to the timing of when they are fertile," Hoover said. "Females, after emerging from the tree where they pupated, require about two weeks of feeding on twigs and leaves before they develop eggs they can lay."
Once the proper ratios of chemical are excreted, it acts as a signal to males that the females are ready to mate.
"What is interesting is that, while the pheromone attracts males, it repels virgin females," Hoover said. "This may be a mechanism to help females avoid competition for a mate."
After synthesizing all for of these essential chemical compounds in the lab and studying the behaviors of the Asian longhorned beetle, the researchers report they may be able to create a solution that attracts the insects but then kills them before they bore into trees to lay their eggs.
"It is possible that the synthetic version of pheromone could be used in combination with an insect pathogenic fungus that is being studied at Cornell University by Ann Hajek," Hoover said. "This fungus can be sprayed on a tree, and when beetles walk on it, they pick up the fungus, which infects and kills them. By also applying the pheromone that female beetles use to attract males, we can trick the male beetles into going to the deadly fungicide rather than to a fertile female."
More research must be done before this system could be implemented, the scientists said. Their preliminary work is published in Journal of Chemical Ecology.