Aphids plague spruce stands

Bad bugs attacking the forest have become a recurring nightmare for Alaska. The latest alarm comes from Halibut Cove, where tiny invaders created an icky spring surprise.

How much of a threat they really pose to the trees and even their exact identities remain to be seen.

Marian Beck, longtime cove resident, noticed that the spruce trees looked unhealthy last year, but the changes were subtle. Then in March, one tree started dropping needles. By May, many spruce were turning brown, and she started making phone calls. She didn’t get helpful answers until she spoke to Mitch Michaud, resource forester for the Natural Resources Conservation Service in Kenai.

Michaud came to the cove in early June, collected samples and concluded that the culprits are most likely green spruce aphids.

These are tiny insects (about 1/25th of an inch long) that suck the sap out of mature spruce needles. Although there are informal reports of these aphids showing up before on the Kenai Peninsula, usually in imported ornamental plants such as blue spruce, this is the first documented outbreak of them in wild trees here, he said.

After talking to him, cove residents went to the forest looking for insects, Beck said. She took along a magnifier loupe to examine the stricken spruce boughs and made a creepy discovery.

“Actually the trees were covered with green aphids,” she said. “But you couldn’t see them with the naked eye.”

Aphid outbreaks are linked to mild winter weather, such as Alaska has had the past couple of years. 

 

Beck noted that they are showing up in places known to remain relatively warm and sheltered in the winter. 

She thinks the aphids remained active, sucking on trees and reproducing during the months when other insects were dormant.

After her discovery in Halibut Cove, Beck asked around and found numerous places on both sides of Kachemak Bay where spruce are suffering the same symptoms. Mossy Kilcher from Seaside Farm in Kachemak City also sent samples to the NRCS. No one knows how long the aphids have been in the area or how far they have spread, Beck said.

Michaud has been discussing the aphids with other specialists. He passed the samples to Matt Bowser, the entomologist at the Kenai National Wildlife Refuge, who is sending them out of state to an aphid specialist for analysis. That is the only absolutely certain way to identify the species, but all the clues so far identify them as spruce aphids.

“It’s highly probable that is what it is,” Michaud said.

On Tuesday, Bowser and three others scientists from the U.S. Forest Service and state forestry visited the Homer area to examine trees on the north side of the bay. “These aphids appear to have caused damage to only a very limited handful of Sitka spruce in the Homer area, but the damage was in some cases severe, possibly killing the trees,” Bowser  said in an email.

More serious problems could arise if additional pests living in the area, such as spruce-bark beetles, attack trees already stressed by aphids and dry weather. People don’t have any effective way to combat the aphids on a forest scale, Michaud said.

Sometimes called plant lice, aphids are members of a common insect family. They go through a life cycle with several stages, appearing as individuals of diverse sizes with or without wings. Most are small and camouflaged to match the plants they infest.

The spruce aphids studied elsewhere in Alaska, like biting mosquitoes, turn out to be all female. They lost their males somewhere along their evolutionary journey. Each can churn out daughters that are clones of herself, meaning that a single insect can give rise to an entire swarm under favorable circumstances.

The spruce aphids are most prominent in the spring and fall rather than summer. This is an adaptation to avoid predators, Michaud said. During the summer, an array of spiders and other insects, such as ladybugs, hunt aphids, which tend to be juicy, fat and slow.

According to the U.S. Forest Service’s guide, “Insects and Diseases of Alaskan Forests,” the spruce aphids (scientific name “Elatobium abietinum”) commonly occur in Southeast Alaska, where they have caused serious damage around Sitka. They are not native to America, but were introduced into the Pacific Northwest from Europe about 100 years ago.

Beck said the aphid infestation is only one of many changes Halibut Cove residents are seeing to the landscape and seascape in recent years. She attributes many of the changes to climate change.

“This is just rolling up the coast,” she said. “We got somebody else’s weather and somebody else’s aphids.”

Michaud stressed that despite the unpleasantness, insect infestations are inevitable, natural and even useful. He predicted that, although Kenai Peninsula residents are still traumatized by the massive spruce-bark beetle outbreak in the 1990s, this new outbreak is likely to be minor. He compared the insect infestations to storms.

“It is very healthy for a forest to be losing trees every year,” he said.

Shana Loshbaugh is a writer who lives on the southern Kenai Peninsula.

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