Foresters consider wasp to counter leaf miners

Posted: Monday, February 10, 2003

ANCHORAGE (AP) -- A parasitic wasp may be introduced in Anchorage next year to counter the explosion of leaf miners decimating leaves of birch trees.

A small sawfly, Profenusa thomsoni, is among several invasive birch leaf miners brought from Europe over the past century into North America. Larval maggots of leaf miners feast on the inner layers of birch leaves. They have damaged more than 30,000 acres of trees in the Anchorage bowl.

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, said Ed Holsten, a research entomologist with the U.S. Forest Service.

''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.''

Aided by warm winters and urban conditions, the leaf miner faced few obstacles in its advance, other than certain pesticides applied to one tree at a time.

By the end of last summer, the infestation had reached down Turnagain Arm, touched the Matanuska Valley and jumped north to Eielson Air Force Base near Fairbanks.

In a biological counterattack, foresters may bring north a tiny parasitic wasp that feeds voraciously on the leaf miner in Canadian birch forests. The wasp is 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.''

Scientists at the federal Animal and Plant Health Inspection Service in Maryland are reviewing Holsten's proposal to see whether it requires federal permits, said spokeswoman Meghan Thomas.

The program would be the first widespread effort to use biological controls to combat the spread of an invasive species out in the open in Alaska, Holsten said.

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