Spruce aphid: Small bugs, big problem

A larger-than-normal seasonal presence has hampered some Juneau inhabitants this spring and summer, impeding members of our locally-rooted population. It isn’t an infestation of tourists causing this problem around Juneau but another invasive species: the spruce aphid.

A warm winter has helped the bug break out in stands of Sitka spruce around Southeast, causing needles to fall off and making trees look like they’re dying.

They’re not, according to U.S. Forest Service entomologist Dr. Elizabeth Graham.

“Even though the tree may look horrible, real scraggly and stuff, it’s actually still alive. They may be stressed but they’re definitely not dead,” Graham said. “The spruce aphid only feeds on the older growth, the older foliage. There’s always new growth coming out and they can’t feed on that new foliage. If you look at the buds, as long as they have the new growth coming out, the trees are still alive.”

Spruce aphid have been in Southeast Alaska at least as far back as 1927 when they were discovered in Wrangell. Regular outbreaks have occurred after warm winters for more than 50 years.

“We’ve had outbreaks of spruce aphid in Southeast Alaska pretty regularly since the 1960s,” Graham said. “It’s mostly controlled by temperature because they actually come out and start feeding in the late winter, early spring. If we have freezing temps during those time periods, the aphid can’t feed so they actually starve and die, so we have the population controlled in that way. Since we’ve had these mild winters the last few years, the populations have been able to build up quite a bit, so we’re seeing the impacts of that now.”

Graham cites heavy outbreaks in 1998, 2000, 2001, 2003 and 2010.

Southeast Alaska’s all-female population of Elatobium abietinum (they reproduce asexually) give birth to live young, which is rare in the insect world, and use their piercing, straw-like mouthparts to feed off older spruce needles.

Spruce aphids have been moving further north in Alaska lately, creeping up the Kenai Peninsula, but not yet as far north as Anchorage.

“They just discovered it in the last couple years on the Kenai Peninsula. It had been expected to be up there in a big outbreak year in the past, but it had never been confirmed from the ground until now,” Graham said. “In Homer the damage is probably the worst right now, so people are seeing that and there is a lot of concern.”

Graham said that Homer has been in a bit of a panic because many thought the damage was caused by spruce beetles, which, according to a 1999 Forest Service report, were responsible for killing 30 million spruce trees per year at the peak of an Alaska outbreak in the 90s.

“There was a lot of concern (in Homer) when it first appeared because when it’s really heavy it’s quite dramatic,” Graham said. “The trees are very brown, people think the trees are going to die. We were getting calls that people want to cut down their trees because they were concerned it was spruce beetle.”

Juneau residents have been calling Graham with similar concerns “almost everyday.” She says the bug affects urban and coastal areas disproportionately and that Auke Rec is one infestation hot spot. Casey Matney, agriculture and horticulture agent for the Kenai Peninsula with the University of Alaska Fairbanks, says that there are some treatment options for spruce aphid.

“Two ways you can treat spruce aphid is with a bark injection or soil drench,” Matney said. “An insecticide is translocated from the roots or the bark to the needles where the aphid eat it and are poisoned.”

Matney added that most people aren’t attempting treatment and trees are likely to survive an infestation if they aren’t otherwise stressed.

“The general rule of thumb is to make sure you are taking care of the tree well, making sure it has enough water and sun,” Matney said. “If it is taken care of then it is rare to see the tree die from a spruce aphid infestation. A lot of people are letting nature take its course but if you catch an infestation early enough, treatment can stop aphid from doing as much damage.”

Graham said Juneau’s spruce trees could benefit from a couple of cooler winters.

“It causes a lot of panic when there’s a really bad outbreak. … If we could get some good winters again, it would help knock the populations down and give the trees a little time to recover.”

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