Tree of heaven is an invasive species that outcompetes other plants by using allelopathic chemicals. Inset left: Tree of heaven can grow as large at 80 feet tall. Inset right: Seed pods on the tree of heaven are fed on heavily by brown marmorated stinkbug. When that food source runs low, the bugs head for fruit orchards.
For brown marmorated stinkbugs, the tree of heaven appears to be just that—a heavenly place to live.
“They can live there and rear their young there—they have absolutely no incentive to go anywhere else,” says Tim Lampasona, a research assistant at Cornell University’s Hudson Valley Laboratory in Highland, New York. Lampasona works in the entomology lab of Peter Jentsch, and he recently spoke to members of the International Fruit Tree Association during a visit to the lab. Researchers at the lab now think that tree of heaven may be a much-preferred host of brown marmorated stinkbug.
So, why do the stinkbugs leave the tree and go elsewhere? Population pressure, mostly, Lampasona said. Their populations build up, and pretty soon they need to look for food elsewhere—and that’s what brings them into fruit growers’ orchards, where they are highly unwelcome. Feeding on developing seedpods in the tree of heaven earlier in the season decreases food quality, which may also prompt insects to move to other food resources, Jentsch said.
He thinks the stinkbug’s strong preference for tree of heaven creates the potential for it to be used as a trap tree and thus a management tool. If the trees were treated periodically using systemic injections to kill the bugs, populations would not reach levels at which the stinkbugs left to find food elsewhere.
Tree of heaven can reach 80 feet tall. It has sumac-like leaves and flowers, although the flower bunches are less compact than sumac. Like the brown marmorated stinkbug, tree of heaven hails from China and Southeast Asia. It was brought to the United States in 1784, 40 years after its introduction in Europe. In China it is called chouchun (literally meaning foul-smelling tree) and is used in many traditional Chinese medicines.
The tree, Ailanthus altissima, was originally planted as an ornamental for its colorful fall seed cluster, but the male tree smells foul, and the tree sets seed prolifically and is aggressively invasive, spreading quickly to disturbed areas and suppressing competition by producing allelopathic chemicals. It regrows quickly from sprouts and is hard to eradicate. It is considered a noxious weed in many areas.
When Oregon State University entomologist Dr. Peter Shearer first saw the brown marmorated stinkbug in Hood River, Oregon, it was in tree of heaven.
That was true in the Hudson Valley as well. The tree was found to harbor high populations of brown marmorated stinkbug throughout the growing season and to complete two full generations there, Jentsch wrote in a progress report on his work with the stinkbug. Highest numbers were found feeding and developing on the female A. altissima fruiting clusters. In one of three monitored orchards where the stinkbug was found to live on A. altissima, it did not migrate to feed on tree fruit; it stayed on the tree of heaven.
“On farms where A. altissima was absent from deciduous woodlands or hedgerows bordering tree fruit, adult stinkbugs emerged from the arboreal habitat late in the growing season to move into and feed intensively on apple,” Jentsch said. “These late-season populations caused severe economic injury on three farms in Ulster and Orange counties.”
Last year, the Jentsch lab conducted a trap tree study. Using commercially available insecticide injection and implant products, commonly used in ornamental insect pest management, the insecticide Acephate was introduced shortly after fruit set. A second application was made at the onset of the second generation.
A substantial number of stinkbugs were killed in the treated trees. Jentsch said using insecticide injections to reduce the numbers of stinkbugs on trees of heaven might result in lower populations and better tree health, and make the tree more attractive to the stinkbugs so they don’t migrate to orchards.
Jentsch chose tree injection instead of spraying because it would be very difficult to manage these wild trees, which may not be on property usually managed for agriculture. He will continue his tests this year to study the importance of this tree as a primary host of the brown marmorated stinkbug.