UNIVERSITY PARK, Pa. -- Female Asian longhorned beetles lure males to their locations by laying down sex-specific pheromone trails on tree surfaces, according to an international team of researchers. The finding could lead to the development of a tool to manage this invasive pest that affects about 25 tree species in the United States.
"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, professor of entomology, Penn State. "We discovered a pheromone produced by females of this species that could be used to manage the pest."
The researchers isolated and identified four chemicals from the trails of virgin and mated female Asian longhorned beetles -- Anoplophora glabripennis -- that were not found in the trails of males. They found that the pheromone trails contained two major components -- 2-methyldocosane and (Z)-9-tricosene -- and two minor components -- (Z)-9-pentacosene and (Z)-7-pentacosene. The team also found that every trail sample contained all four of these chemical components, although the ratios and amounts changed depending on whether the female was virgin or mated and depending on the female's age.
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."
The researchers found that when the proper ratio and amount of pheromone is produced by females and deposited on the surface where they walk, signaling that they are fertile, males come.
The researchers published their findings in the current issue of the Journal of Chemical Ecology.
"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."
In addition, the researchers learned that sexually mature females continue to produce the trail pheromone after mating, a practice they think benefits both sexes. According to the scientists, by continuing to produce the pheromone after mating, females can lure the same males back to mate again or they can lure other males to them.