Canada wasps may lead attack on city's birch leaf miners
ARBOREAL DRAMA: Foresters plan to import insects to save birches.
adn.com
By Doug O'Harra
Anchorage Daily News
(Published: February 9, 2003)
The amber-marked birch leaf miner has exploded across Anchorage during the past few years, washing out summer's green. Its larval maggots have feasted on the inner layers of birch leaves, damaging more than 30,000 acres of trees in the Anchorage Bowl, said Ed Holsten, a research entomologist with the U.S. Forest Service here.
But this leaf-munching orgy by an alien pest may be about to end.
In a biological counterattack by local foresters, a tiny parasitic wasp that feeds voraciously on this leaf miner in Canadian birch forests may be collected and released in Anchorage as soon as 2004.
The villain in this arboreal drama is a small sawfly, Profenusa thomsoni, among several invasive birch leaf miners brought from Europe over the past century into North America. The sawflies probably reached Anchorage in the mid-1990s, riding on imported nursery stock. They started spreading fast without predators or parasites here to control the population, Holsten said.
"This insect arrived and found this ecological niche that was vacant, without its complement of biocontrols," Holsten said. "It landed in Anchorage like it was in the middle of a giant salad bar."
Since then, Anchorage's favorite shade tree has been going brown or barren at summer's peak, leaves eaten from the inside by the sawfly larvae. Aided by warm winters and urban conditions, the leaf miner faced few obstacles in its advance across the city, other than certain pesticides applied to one tree at a time by licensed professionals.
By the end of last summer's growing season, the infestation had reached down Turnagain Arm, touched the Matanuska Valley and jumped north to Eielson Air Force Base near Fairbanks.
The hero in this battle of the bugs could be a little-known critter native to eastern Canada and the United States, so obscure that it has only a scientific name: Lathrolestes luteolator.
It is a tiny dark wasp with a wingspan only a few millimeters across.
"They're harmless to people. They don't sting," Holsten said. "They just fly around and look for leaf miner larvae."
The adult female wasp uses a stingerlike ovipositor to penetrate the leaf surface and lay eggs inside the bodies of sawfly larvae while they're still feeding on the leaf's inner layers. The growing wasp remains cocooned within the little green larva when it overwinters in the soil, then finally bursts out as an adult the following summer, when the cycle starts over.
"It's kind of like the 'Alien' movie," Holsten said. "Instead of an adult leaf miner coming out, the chest rips open and out comes an adult wasp."
If approved by federal and state agencies, the project would begin next summer with a detailed study of the leaf miner's life cycle in Anchorage. Meanwhile, Canadian technicians would gather amber-marked leaf miner larvae already carrying wasp eggs, to be brought to Anchorage in 2004 for the first introduction, Holsten said.
"We will probably release these parasites on a caged tree at first," he said. "I imagine if everything works, we're going to take more than one release. It's going to take a while for this parasite to get established."
Holsten is coordinating the proposal with municipal, state, federal and Canadian agencies. Scientists at the federal Animal and Plant Health Inspection Service in Maryland are now reviewing Holsten's proposal to see whether it requires federal permits, said spokeswoman Meghan Thomas.
The program, which could cost about $90,000 over three years, would be the first widespread effort to use biological controls -- deploying a pest's natural enemies -- to combat the spread of an invasive species out in the open in Alaska, Holsten said.
"Biological controls are the best type of controls you can have because they're self sustaining," Holsten said.
In a sense, the recent spread of the birch leaf miner is just a local example of a serious worldwide problem: invasive species that can cause billions of dollars in damage and permanent changes in local ecology. Using biocontrols as a response to pests of all sorts has become increasingly popular as an alternative to pesticides. It's like releasing ladybugs to fight aphids in a garden.
The public greenhouse at Russian Jack Springs Park now uses ladybugs, wasps and midges to control plant pests, said municipal horticulturist Bill Robb. "We haven't had to use pesticides for two years."
On a large scale, the practice has a long and sometimes controversial history in agricultural states such as California, Florida and Hawaii. One danger arises when a species brought into control one pest starts attacking beneficial insects or plants.
For instance, Hawaiian sugarcane farmers introduced parasitic wasps in the early 1900s to fight off introduced pests. Some of those wasp species were discovered decades later feeding on native caterpillars in Kauai swamps, according to a study published in the journal Science in 2001.
The trick for safe biocontrol hinges on picking a species that's very selective about what it eats.
This particular wasp comes highly recommended because it has already conjured a sort of birch tree miracle in Alberta with no unintended munching on beneficial insects, according to interviews with pest specialists in Canada and Alaska.
The amber-marked leaf miner was infesting birch trees in the northern city of Edmonton by the 1970s, prompting the city and homeowners to use pesticides to keep trees green, said Chris Saunders, a biologist with that city's pest management office. It was among three birch miner species that attacked Edmonton's trees for decades.
"At its worst, every birch tree in Edmonton would go brown in mid- to late July," Saunders said. "We saw this (wasp) showing up in the early 1990s, and once it showed up, it basically took the whole problem down and we have not had a problem since."
Not much was known about the wasp at the time. It had previously targeted another species of Profenusa leaf miners feeding on northern red oaks in eastern Canada and the United States, Saunders said.
But no one realized it would attack the amber-marked leaf miner until it showed up in Edmonton on its own, wrote research entomologist David Langor, in an article posted on the web by the Canadian Forest Service. "This is an unusual case."
Its success prompted Langor and Canadian entomologists to import other species of parasitic wasps from Europe to combat other leaf miner species in Alberta, especially the common leaf miner called Fenusa pusilla.
The leaf miner in Anchorage was originally misidentified as this Fenusa species, which can produce two generations per summer and is harder to contain, Holsten said.
Because the Lathrolestes luteolator wasp appears to attack only leaf miners of the Profenusa family, several local pest experts, arborists and gardeners say that releasing it in Anchorage is a good idea with little risk.
"The wasp is a parasite, and like all parasites, they pretty much specialize in one thing," said Rocco Moschetti, a private pest management specialist who supervised the biocontrol at the municipal greenhouse. "It's not harmful to anything else other than the amber-marked birch leaf miner.
"People definitely shouldn't fear using it and should be grateful that there is a parasite for the birch leaf miner out there."
"I think it's a great start," Robb said. "I would wholeheartedly recommend that we use it. ... I cannot think of anything could happen because they're so specific for specific hosts. Once their food supply is exhausted, they drop back to very small levels."
Still, Robb cautioned against expecting a miracle. It might take years for the wasp to spread.
"How fast can they multiply to take care of the problem we have might be one question that we have to resolve," he said.
Doug O'Harra can be reached at do'harra@adn.com and 907-257-4334.
ON THE WEB:
Birch leaf miner controls in Edmonton, Alberta: www.edmonton.ca/comm_services/parkland_services/pest_management/birch_leafminer_control.html
Background information on biocontrols by IPM of Alaska: www.ipmofalaska.homestead.com/files/biocontrol.html
Canadian Forest Service: www.nrcan.gc.ca/cfs-scf/national/what-quoi/Solutions/english/01sawflies_e.html |
