May 1, 2007
Non-Native Ambrosia Beetle Threatens Redbay Trees
By Leslie Kimel
A tiny beetle no larger than a match head is posing a big threat to Florida’s forests.
In late 2004, redbay trees (Persea borbonia) began mysteriously dying on Fort George Island in the Timucuan Ecological and Historic Preserve just northeast of Jacksonville. As the months passed, dead redbays kept appearing further and further inland, and by the summer of 2005, 80 percent of the preserve’s monitored redbays were dead.
The trees, it was discovered, were killed by a fungus spread by the redbay ambrosia beetle, Xyleborus glabratus, a recent, unintentional import from Asia. The beetle likely arrived in the U.S. in wooden pallets and packing crates. Though it first showed up in insect survey traps at Port Wentworth, Georgia, in 2002, it wasn’t connected to the deaths of redbays until years later. Today it is found along the Atlantic coast from Charleston to St. Augustine, and tens of thousands of redbays have died.
“In areas where this new beetle is becoming established, it seems that all the mature redbays are being wiped out,” said Bud Mayfield, an entomologist with the Florida Division of Forestry.
Female beetles carry spores of the fungus in sacs at the base of their mouth parts. By attacking small branches, the females inoculate trees with the fungus. The fungus clogs a tree’s water-conducting tissue, causing the leaves to wilt and the tree to die. Beetles tunnel into the dying tree in order to reproduce, “gardens” of fungus providing food for the larvae and adults. No wood is eaten.
Because the redbay ambrosia beetle comes from far away, it has no natural enemies in Florida to keep it in check.
“Native ambrosia beetles typically attack only dead and dying trees, and they’re a natural part of replacing those weaker trees in the forest,” Mayfield said. “In contrast, this new ambrosia beetle and its associated fungus are not a natural part of our forests, and it appears that even healthy redbay trees are vulnerable to them.”
Right now, there is no way to stop the beetle, forestry officials say. But care should be taken not to hasten its spread. Dead redbay trees in yards and gardens should be chipped and left onsite as mulch, and campers are asked not to move redbay firewood from place to place.
Sassafras, avocado, and other trees related to the redbay could also be at risk for infestation.
Redbay is an attractive evergreen tree that reaches an average height of about 30 feet. The thick, lustrous, bright green leaves are lance-shaped, with smooth edges and a spicy fragrance. Inconspicuous small greenish-yellow flowers bloom in summer, and shiny blue to black fruits—each about half an inch long—ripen in fall.
Graceful, shady, and drought tolerant, redbay is a popular choice for residential and commercial landscapes. The wood is sometimes used in cabinetmaking, and the aromatic leaves can be dried and used in cooking.
Redbay may not have a whole lot of significance economically, but it is extremely important ecologically. White-tailed deer browse the leaves and eat the fruits. The fruits are also consumed by songbirds, wild turkeys, bobwhite quail, and black bears. Female palamedes swallowtails lay their eggs on redbays and swampbays (Persea palustris). If a butterfly can’t find its host plant, no other plant will do as a substitute.
“Redbays belong here,” said Richard Bryant, Chief of Resource Management at Timucuan Ecological and Historic Preserve. “They’ve been here for eons. They’re part of this system.”
No one knows exactly what will happen if they’re gone.
“Birds eat the berries,” Bryant said. “Will those birds leave? Butterflies need that tree to have their young larval stages. Will other species drop out without the redbay here?”
