AUGUSTA, Maine — Last year’s unusually warm winter may have kept heating bills down but did come with a price: the continued northeasterly spread of an invasive pest that could ravage Maine’s hemlock trees, according to forest service officials.
Hemlock woolly adelgids have been found in 13 towns since May in Cumberland, Sagadahoc and Lincoln counties. Maine Forest Service entomologist Allison Kanoti said this week that she expects that list to grow as summer interns continue to survey the coastline in Knox County next week.
“In areas to our south, the decline and mortality of hemlock in infested stands can really be quite shocking,” she said. “To this point in Maine, we have not seen that level of impact, although we do see decline.”
The tiny insect, originally from Japan, was brought to the eastern United States sometime before the 1920s, she said. An infestation that began about 10 years ago when bugs came to Maine on infected nursery stock did not lead to a widespread problem with wild trees, according to Kanoti, but winds and birds have been spread-ing the insects more naturally since 2003, when they were spotted in York County.
Eastern and Carolina hemlock trees have no natural protection against the bugs, which form white, woolly egg sacks that look like the tops of cotton swabs. They are unusual in that there are no male woolly adelgids — all are female and reproduce asexually. Each bug can have up to 300 eggs in the cottony egg sack, with each egg a clone of its mother.
“You only need one to start a population,” Kanoti said. “Our hope is basically to be able to slow the spread as much as possible. We really do ask people to look at their hemlocks for signs of the insects.”
In this part of the country, hemlock woolly adelgids feed only on hemlock trees, eating the sap the tree needs to grow and sustain itself.
When the bugs are present, they cause their host trees to lose needles and also cause the crowns to thin, which could be devastating to Maine ecosystems, said Acadia National Park natural resource specialist Judy Hazen Connery.
“We’re very concerned about this insect. It has the potential to really seriously injure our hemlock stands,” she said. “Hemlock is a keystone species in our forest. It’s very, very important in maintaining temperature control.”
The hemlock’s dense green canopy shades and cools the forest floor and streams, thereby helping species such as brook trout and deer to thrive, Kanoti said.
Warmer-than-average winter weather is one reason the adelgids have been moving north, she said. Four of the last five winters have been warmer than normal, and last winter was 6.2 degrees warmer than the average, according to the Northeast Regional Climate Center at Cornell University.
“The reason we have not today seen the level of mortality as in the south is our climate — our cool winters,” Kanoti said. “The warm winters have allowed populations to build up. It’s now detectable in areas it hasn’t been in the past.”
The entomologist noted that the insect’s path through Maine is taking it northeasterly, along the coastline, where temperatures are generally more temperate in the winter.
A fungal insecticide is being developed and there are chemicals that can be used to manage the insects to a point where tree health can be maintained, Kanoti said. It also is possible to use a rigorously monitored beetle that is an adelgid predator to help control infestations, she said.
According to Connery, the insect has caused great destruction to the hemlocks of other national parks farther south, including Shenandoah and the Great Smoky Mountains, which have many old-growth stands of hemlock.
“It’s so important for people to keep their eyes and ears open for this insect,” she said. “There is hope — but that hope lies in early detection and rapid response.”
The Maine Forest Service is asking people to look for signs of the hemlock woolly adelgid, which include a cottony, woolly growth pattern that has formed on the newest hemlock twigs.
Service officials also request that people not move live hemlock material if the tree is in an infested area.
For more information or to report a possible infestation, call Allison Kanoti at 287-3147.