Race to find damaging beetles turns to radar
It is a double curse of the reviled Asian longhorned beetle: Not only are the hole-boring insects deadly to trees, they are also usually detected long after an infestation has taken hold in an area, requiring enormous numbers of maples and other hardwoods to be removed.
Now, with the invasive pest recently discovered in Boston, a Northeastern University professor and an undergraduate are attempting to devise a way to find the beetle earlier. Carey Rappaport, professor of electrical and computer engineering, and sophomore Kassi Stein are developing a radar collar that can be wrapped around a tree trunk.
The collar would beam microwaves into the tree, and sensors would show any dry voids, which signal that Asian longhorned larvae have probably begun feeding inside the tree.
If it works, the collar could help identify infested trees far sooner, allowing them to be cut down before an entire neighborhood’s trees — or a forest — are consumed by the voracious bugs. The duo are still in the very early stages of modeling the idea, but hope to build a prototype in the next year.
“I have three nice maple trees in my yard; I’m motivated,’’ Rappaport said. “The biggest waste is chopping down a tree that doesn’t need to be chopped.’’
In Boston, an eagle-eyed Faulkner Hospital groundskeeper spotted sawdust around trees, a sign the bug was feeding inside. State officials hope the infestation is limited to six trees bordering a parking lot.
Generally, infested trees are spotted only when adult beetles emerge from a dying tree, leaving large holes behind. By that time, beetles have usually moved on to attack new trees.
Once that happens, as in a beetle infestation discovered in Worcester two years ago, officials have no choice but to remove trees because the insect has no predator in this country. Some 25,000 trees have been cut down in Worcester and surrounding areas at a cost of about $50 million.
Other ongoing projects might improve detection of this white-speckled black beetle, according to a 2010 Annual Review of Entomology paper, led by Robert Haack of the USDA Forest Service’s Northern Research Station in Michigan.
Scientists are working to identify pheromones of male and female beetles in an effort to set out lures that would trap them.
Research in China and elsewhere found that some species of trees — especially drought-stressed ones — attracted the beetle more than others. Scientists are now testing a species of Asian maple that is highly attractive to the beetles to see whether it could be used to detect them, according to the paper.
Haack and others also have attempted to find infested trees using hand-held devices with acoustic sensors that can distinguish the feeding sounds made by larvae of the Asian longhorned beetle from the sounds of other insect borers. The devices have been used in New York’s Central Park, but have limitations. For example, beetles don’t tend to feed when it’s colder than 50 degrees, and the devices usually have to be within 20 feet of a larva.
“The trunk of a tree can get pretty noisy,’’ Haack said, given that other environmental sounds, such as woodpecker tapping and nearby traffic, can also be detected.
Haack said the devices are being examined as a way to augment other detection methods. For example, if someone finds an adult beetle but can’t determine which tree it came from, the devices could be used to listen for feeding in nearby trees.
Haack and other scientists still say the best way to detect the beetle is by visually inspecting trees for tiny pits bored into the bark to allow adults to lay eggs and for adult exit holes.
A team has begun examining upward of 100,000 trees near Faulkner Hospital for the beetle. Officials have also asked residents to examine trees in their yards and neighborhoods.
(They are asking the public to report signs of the insect by calling a toll-free hotline, 866-702-9938.)
“Every detection thus far has been found by citizens,’’ said Rhonda Santos, a spokeswoman for the US Department of Agriculture, which is overseeing the fight to eradicate the beetle. “It’s great to have all these other ideas and studies, but we still come back to visual surveys right now as the most reliable.’’
Beth Daley can be reached at firstname.lastname@example.org.