Gathering seeks sawfly solutions

Insects left swaths of ruined trees this year

Posted 11/18/14

Citizens looking for answers to Elbert County's pine sawfly infestations gathered at the Elbert County Fairgrounds Exhibition Hall in Kiowa on Nov. 15 to hear presentations about the insect's life cycle, prevention, and options for treating infested …

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Gathering seeks sawfly solutions

Insects left swaths of ruined trees this year

Posted

Citizens looking for answers to Elbert County's pine sawfly infestations gathered at the Elbert County Fairgrounds Exhibition Hall in Kiowa on Nov. 15 to hear presentations about the insect's life cycle, prevention, and options for treating infested trees.

“This year there was a mega outbreak, and it caught everyone by surprise,” said Bill Ciesla, a forest protection specialist, to the gathering of more than 60 residents who attended the meeting. “As far as I know, we have never seen damage like we have seen this year.”

Pine sawflies have been in Elbert and El Paso counties for more than a decade. The area is particularly attractive to this species of sawfly because the trees tend to be spread out, and the soil is sandy and easy to burrow. This year, aerial surveys mapped 7,400 acres of infested trees.

“The sawfly is inconspicuous,” Ciesla said. “But there have been so many of them this year that you can see them flying around.”

Outbreaks causing small amounts of deforestation occurred in 2005 and 2009, but as far as Ciesla can recall, the summer of 2014 was by far the worst he has seen. In some cases, huge sawfly colonies stripped trees before the larvae were mature enough to burrow in the ground. According to Ciesla, each year was so different that it is hard to pinpoint the cause of any of the outbreaks.

The pine sawfly is named for the distinctive saw-toothed shape of the female's ovipositor, an organ she uses to cut into pine needles to lay eggs. Neodiprion, the species of pine sawfly found in Elbert County, is so new that it has no common name. Discovered around 1995, this species is indigenous to North America, has a one-year life cycle, and resembles a primitive wasp though it has no stinger and is harmless to humans and animals.

In the United States, this sawfly feeds on ponderosa pine needles, but it is also found on other types of evergreens growing in Mexico. Its four-stage life cycle begins in the fall when adult females lay eggs on the pine needles.

The eggs are not destroyed by the extreme cold of winter and remain on the needles until they hatch in the spring, typically during a two-month window in May and June. The larvae gather into colonies to feed on the outer needle tissue, leaving the central ribs. As they mature, they grow from the size of a tiny drop of dew to an inch or longer. A caterpillar-shaped body with a large orange head makes them easy to identify, and when threatened, they rear up in unison and blow tacky bubbles of pine resin as a defense mechanism.

After about two months of feeding, mature larvae drop to the ground and burrow into the soil to spin a cocoon, entering a pupal stage where, like a butterfly or moth, the larvae transform into adults. The males emerge from the pupal stage thin and agile while females emerge from their cocoons laden with more than 200 eggs and are sluggish fliers until they lay at least some of the eggs. After that, both are strong flyers and, using wind currents, can easily move into uninfested stands of trees.

Ciesla warned that moderate to heavy infestations weaken trees, making them vulnerable to secondary attacks by bark beetles.

Like any indigenous species, this variety of pine sawfly has natural predators, specifically mice, a species of parasitic wasp, and a nuclear polyhedrosis virus, which attacks the larvae.

According to Meg Halford, assistant district forester with Colorado State University's Extension Office who also addressed the group, the sawfly's natural predators are not enough to stave off moderate to heavy infestations.

While there is no current plan beyond monitoring the progression of the sawflies, Halford suggested several courses of action that individual property owners can do to protect their trees.

Halford advises watching trees for infestations, which become visible when the larvae hatch. Larvae start small, but colonies can be easily seen. For small infestations, a simple hose and sprayer has been found effective for clearing most of the larvae from trees. Halford recommends starting at the top and working down. Spraying is no longer effective after the larvae mature and naturally drop to the ground.

“Timing is crucial,” Halford said. “The time to spray is in May and June while the larvae are feeding.”

Once knocked to the ground and away from their food supply, immature larvae will die. One resident found that mixing dish soap with water was effective for cleaning larva from his trees, suggesting a mix of one quart of Dawn to 300 gallons of water.

Chemical pesticides such as acephate and permethrin are effective at killing the larvae, but these broad-spectrum pesticides also kill other insects, such as bees.

“If you're going to mix it (chemicals) yourself, follow the directions,” Halford said. “Upping the concentration does no good, and you're just spraying your money into the air. Be sure to wear PPE (personal protection equipment). These are chemicals.”

For property owners uncomfortable with the idea of mixing poisonous chemicals or lacking the equipment to reach taller trees, she recommends hiring a professional.

Aerial spraying is also an option for larger properties. Halford encourages property owners to coordinate their efforts to defray the cost and to notify neighbors that pesticides will be sprayed in the area.

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