Bug busters
City seeks solutions to rid birch trees of leaf miner

Tara Kearsey
Northern News Services

Yellowknife (Aug 16/00) - City officials have sent birch leaf samples to Edmonton for scientific analysis to determine if anything can be done to help hundreds of local birch trees that have been infested with the pesky leaf miner.

The insect, known as the sawfly, has been preying on local trees for at least 10 years, but signs of the infestation have become more severe this summer.

Everywhere you turn in Yellowknife, the leaves of birches are plagued with large brown blotches and tiny black insects. Some trees have been so badly attacked, the surface layer of its leaves can be peeled back without much effort.

"(The problem) is certainly widespread and growing," said Tim Mercer, the city's director of corporate services.

Mercer said leaf miner activity has been monitored by the city over the past three years.

"It's really overwhelmed the city," said facilities manager Tony Burge.

He believes the infestation is more severe this year because the insect is in its third generation.

"Usually they only come in two generations but we've got stuck with the third one.

"They are all over (the city) and a lot of that has to do with the dry summer and not much rainfall," said Burge.

The leaf miner is not native to North America. The insect was inadvertently transported from Europe in the early part of the 20th century.

Although the pest makes the birch not so appealing to the eye, the leaf miner does not normally cause serious damage to the health of the tree. However, if an infected tree experiences repetitive attacks, does not get enough moisture and is attacked by other insects, the branches of the tree could perish.

City officials are considering two possible options to kill off the leaf miner. The first is use of a pesticide known as Cygon 2E, but the chemical is highly toxic and poses serious safety hazards if inhaled, ingested or comes into contact with the skin.

The second is the introduction of a parasitic wasp known as the lathrolestes luteolator. The wasp preys only on one of the three species of leaf miner and presents no threat to humans. A recent outbreak of birch leaf miner in Edmonton was successfully controlled by this wasp, which reduced the infestation by up to 95 per cent.

Burge said 50 infected leaves have been sent to Edmonton for analysis. If scientists discover this particular species of leaf miner can be controlled by the wasp, he said, city officials will conduct research to determine if it should be introduced to Yellowknife next year.