The aggressive Redbay Ambrosia beetle is no bigger than Abraham Lincoln’s nose on a penny, but over the last two decades, the invasive insect has managed to kill more than 500 million trees in North America – and now it has arrived on Long Island, bringing its disease, laurel wilt, along with it.
Experts postulate that the dark-brown bug migrated north via firewood brought in from southern states where the insect has decimated sassafras, spicebush, camphor, swampbay, redbay and avocado trees. Aside from the loss of tree canopy, these decimated forests have a deep ecological impact because endangered pollinators such as butterflies depend on these plants for survival.
”The impact was just unseen before, and it was, and just unbelievably rapid, almost like some other type of natural disturbance like a hurricane or a fire,” said Jason Smith, a forest pathologist and a professor at the University of Mount Union.
There is no definitive number of how many trees have been affected so far in New York, according to the state’s Department of Environmental Conservation. The state is still conducting its initial survey. So far, they’ve found 700 trees wilting or dead from the disease out of an examination of 2,000.
The disease was first discovered in New York in Northport, but has been found in other Suffolk County towns, including Dix Hills, Hauppauge, St. James and Greenlawn.
Laurel wilt was first detected in the United States in Savannah, Georgia, in 2002. The fungus can kill a tree within weeks. Some of its rapid devastation includes wiping out more than 90% of the redbay trees in Florida forests. The current spread includes 12 states.
The disease cycle begins with the cigar-shaped beetle landing on a tree. They are attracted to mature, larger trees, but are not limited by size or age. The bug carries fungus spores inside its body at the base of each mandible. The beetle burrows into the tree’s sapwood, where the fungus can germinate in the wood. The spores rapidly colonize and disperse within the tree. The female cultivates the fungus alongside her eggs in a symbiotic relationship. When the eggs hatch, the young feed on the fungus.
“The Redbay Ambrosia beetles can be thought of as fungus farmers,” Bud Mayfield, a Research Entomologist at the US Forest Service, said.
In reaction to the fungal invasion, the tree closes off its water-conducting cells, and its sapwood will darken. The tree will wilt and weaken, essentially killing itself in an overreactive response to the fungal presence, similar to what happens when a tree is struck with Dutch elm disease. The foliage will take on a look of early fall with leaves browning and withering.
Other beetle species will flock to the ailing tree, attracted by the scent of ethanol, which many trees give off when sick. According to the Forest Service, the introduction of a single host led to the death of half a million redbay trees.
Streaks in the sapwood and evidence of the fungus that causes laurel wilt.
”It's not surprising that if a sassafras is wilting from laurel wilt, it's going to be stressed and attract these other opportunistic beetles,” Andrew Lloyd, plant pathologist at Bartlett Tree Research Laboratories, said.
The beetle is native to Southeast Asia, specifically Taiwan. In its native range, it only attacks trees that are already dying. But in North America, they attack healthy mature trees.
“It's not what ambrosia beetles typically do. The fungi aren't typically pathogens,” Smith said. “We have a completely novel relationship going on here due to the introduction of an organism into a new environment, and that is unprecedented.”
In less than five years, the beetles can wipe out a forest of these species.
“The mortality rate was almost a hundred percent within four or five years,” Smith said. “You could see the damage from helicopter surveys and it looked like wildfire had moved through.”
There is no silver bullet for eradicating the Redbay Ambrosia beetle and its fungal crop. The insect is vulnerable to the cold, but the temperature would have to reach at least 23 degrees Fahrenheit for over 24 hours to kill off the bug, and Long Island doesn’t typically get that cold during the winter.
Experts are in the early stages of trying out some options for controlling the pest. Lloyd said one possibility to slow the spread is the selective removal of infected trees.
Researchers at the US Forest Service have done preliminary tests injecting a commercially available fungicide called Propiconazole into healthy trees as a preventive measure, like a vaccine.
This is already approved by the state, but requires an injection every two years, and does not work on diseased trees and is not a viable option to save a forest. This is recommended for trees with high economic value or single trees on private properties.
For diseased trees, there is no known cure, but limited success can be achieved by chipping the tree into small one-inch pieces. The fungus is unable to survive in a tree once it’s been broken down into tiny pieces, and this will significantly reduce the beetle population living in the wood.
”This beetle has the biology and adaptation to survive and complete its entire lifecycle in a tree that's protected under a high moisture regime and high pressure,” Lloyd said. “Once it gets chipped, you're no longer in this closed system, and so the fungus isn't also able to compete with other, you know, secondary wood-degrading fungi, so it dies and the beetles can't survive and complete their lifecycle outside of an intact host.”
The NY Department of Environmental Conservation is actively investigating the spread of the insect. Cures and management practices are limited and in early stages of development.
The disease is only confirmed on Long Island. The DEC has not detected the disease in the Hudson Valley or New York City, where spicebush and sassafras trees are very common in parks such as Van Cortlandt Park and the Highline. Residents should report any suspected cases to the DEC.
In New York, especially on Long Island, there has been a lot of recent introduction of invasive species, including southern pine beetles wiping out pitch pines and beech leaf disease decimating the beech trees.
“Diseases are wreaking havoc,” Lloyd said. “When you think about forest canopy and forest health, having mass die off all at a very rapid rate can shift things very quickly for a lot of wildlife that depend on them, as well as erosion control.”
