Does Chipping Pine Attract Bark Beetles?

Lop and scatter method of slash disposal
Lop and scatter method of slash disposal. Photo: USDA

As many forest landowners already know, pine slash has a tendency to attract pine bark beetles. There are several recommendations for slash disposal to mitigate this problem. Two common methods — lop and scatter, and chipping — focus on eliminating bark beetle habitat while retaining the nutrients contained within the slash on site.

The lop and scatter method involves cutting slash into smaller pieces (less than 12 inches in length, less than 3 inches diameter) and scattering the pieces throughout the site. Chipping involves running slash through a chipper and scattering it throughout the site, similar to lop and scatter. While there is no chance that bark beetles can infest the chips, it is still possible for bark beetles to infest the pieces in the lop and scatter method. The chances of the beetles being able to successfully produce brood in these pieces is pretty low, as they will likely dry out before the larvae are finished developing. Both methods are a reasonable substitute to piling and burning when burning is prohibited, BUT…

Anytime you cut pine, you are releasing volatiles. Volatiles emitted from pine contain chemicals called monoterpenes. Some monoterpenes have been shown to attract bark beetles and are often included as part of the lure when trapping for bark beetles.

female bark beetle
A female bark beetle eating the phloem of a tree. Photo: USFS

If you are choosing between lop and scatter and chipping, which is best? You would think that chipping would be the better choice since there is no chance that bark beetles can infest the chips. But a study by Fettig et al. (2006) showed that chipping in ponderosa pine stands attracted bark beetles more so than the lop and scatter method, particularly in the spring. Why would this be? As it turns out, directly following treatment chipping releases much larger quantities of attractive monoterpenes than the lop and scatter method. If large quantities of attractive monoterpenes are released at a site where the slash has been chipped and bark beetles arrive, where are they going to go? They cannot infest the chips. They are going to go to the standing, residual trees. Although the act of thinning should increase the health and vigor of the residual trees, it will take at least a year for those trees to respond, therefore, you may wind up with bark beetle infested leave trees.

So, does this mean you cannot chip? Not necessarily. Some landowners prefer to begin thinning treatments on their property in the spring; it is finally warm (but not too warm), the snow is melting off, and they are ready to go outside and get things done. Other landowners find that they have to thin in the spring for various reasons (the snow is too deep during the winter; fire season often prohibits the use of machinery in the summer; contractors cannot fit everyone in during the bark beetle “off” season). Unfortunately, as Fettig et al. (2006) found, the response of bark beetles to high concentrations of volatiles released from chips is more significant in the spring because a large segment of the beetle population is most active during this time.

If you plan on chipping, it would be best to avoid treatments in the spring. The best time to chip (or do any sort of management that releases pine volatiles for that matter, including pruning), would be in late summer (late July/early August) through early winter (December). When producing chips, avoid piling them and absolutely do not pile chips at the base of any residual trees.  Spread the chips out in the sun if you can. The quicker they dry out, the quicker the volatiles will dry out, and the less overall bark beetle risk there will be.

By Melissa Fischer, forest health specialist Washington State Department of Natural Resources, Northeast Region, melissa.fischer@dnr.wa.gov

References

Fettig, C.J., J.D. McMillin, J.A. Anhold, S.M. Hamud, R.R. Borys, C.P. Dabney, and S.J. Seybold. 2006. The effects of mechanical fuel reduction treatments on the activity of bark beetles (Coleoptera: Scolytidae) infesting ponderosa pine. Forest Ecology and Management. 230: 55-68.

Are Those “Stink Bugs” in Your Home?

Since September, I have been awakened from a dead sleep countless times by an obnoxious buzzing in my ear and, even more unsettling, the feeling that something is crawling on top of my head. Although groggy, I usually realize pretty quickly that it’s just a stink bug, grab it, and toss it across the room. Admittedly, this method of disposal did backfire once when the stink bug turned out to be a paper wasp; a regrettable mistake.

So what are these annoying insects? Why are they in our homes?

 Consperse stink bug
Figure 1. The Consperse stink bug (Euschistus conspersus) Photo: Mike Quinn, Bugguide.net

You may be surprised to find out that these insects are not actually stink bugs. Stink bugs are in the family Pentatomidae and have bodies shaped like shields (Figure 1). The insect in question is actually in the family Coreidae, or the leaf-footed bugs. The common name “leaf-footed” refers to the enlarged leaf-like structure on their hind legs (Figure 2). The genus and species of this particular leaf-footed bug is Leptoglossus occidentalis whose common name is the western conifer seed bug (WCSB).

Although you may be familiar with the WCSB because of its presence in your house, this insect is actually a forest dweller. The WCSB feeds on seeds, developing cones and the needles of pine trees, as well as Douglas-fir.

Western conifer seed bug
Figure 2. The Western conifer seed bug; notice the leaf-like structure on the hind legs. Photo: Bugguide.net

The WCSB has a single generation a year. Adults emerge in late May or early June. At this time, they feed on one-year-old cones and inflorescences (small flower clusters). Eggs are laid in rows on conifer needles and hatch within 10 days. The WCSB is a “true” bug in the order Hemiptera and does not go through complete metamorphosis as a fly or butterfly would. In other words, there is no larval stage. Instead, the young look very similar to the adults, only smaller, and are called nymphs rather than larvae (Figure 3).

The WCSB goes through five nymphal instars (stages) prior to the final adult stage. The first instar feeds on needles and cone scales while older nymphs will feed on developing seeds. The WCSB reaches adulthood around mid-August and will continue to feed on ripening seeds until early fall, after which time it will begin to seek overwintering sites. This is when you may begin seeing them in your home. The WCSB will overwinter under bark, in dead and dry logs, in bird and rodent nests, and of course, in buildings. With its flattened body shape, it can enter a house through most small openings. Once inside the house, they tend to become active and conspicuous when warm.

Nymphal stages and final adult form of the Western conifer seed bug
Figure 3. Two nymphal stages (on the left) and the final adult form (far right) of the Western conifer seed bug. Photo: Brandon Woo

Although annoying, the WCSB is not harmful to people. It does not bite, sting, eat wood, or breed indoors. It does emit an unpleasant odor when disturbed, but this is not harmful to anything but our noses. The tendency to think that WCSB is harmful may be due to a case of mistaken identity, as leaf-footed bugs have a similar appearance to assassin bugs (family Reduviidae), which do bite. There are morphological differences that distinguish WCSB from assassin bugs; the most obvious is the leaf-like structure found on the hind legs of the seed bug, which assassin bugs lack (Figure 4).

Assassin bug
Figure 4. Assassin bug Sinea diadema; notice the lack of the leaf-like structure on the hind legs, which the Western conifer seed bug possesses. Photo: Michael Hughes, Bugguide.net

The WCSB can be a pest to the forest industry, particularly in seed orchards, as it can result in a substantial loss of seed crop. However, in a general forested setting, there are typically plenty of seeds to go around and there is no lack of regeneration in our forests as a result of these bugs.

So, is there any way to control the WCSB? The best method of control is prevention via mechanical exclusion. This of course would involve filling in any cracks around the house where they may be getting in. Replacing loose screens, windows and doors; caulk gaps; and screen your fireplace, attic and wall vents, and other openings — basically, blocking all points of entry. Unfortunately, if your house is anything like mine, this is a near impossible endeavor. I opt for the vacuum cleaner and just suck them up.

By Melissa Fischer, forest health specialist, Washington State Department of Natural Resources, Northeast Region, melissa.fischer@dnr.wa.gov 

Blue Spruce Damage Indicates Elevated Risk of Douglas-fir Tussock Moth Outbreak

Douglas-fir tussock moth
Source: Forest Health Highlights in Washington, 2016, by DNR and U.S. Forest Service.

Recently I have begun to observe damage to ornamental blue spruce throughout the area of Colville, Washington. Upon closer inspection of these trees, I found that they are being defoliated by the Douglas-fir tussock moth. The Douglas-fir tussock moth is a native defoliator of Douglas-fir, true firs (such as grand fir) and spruce. For reasons unknown, a year or two prior to an outbreak of Douglas-fir tussock moth on forested land, we tend to see defoliation of ornamental trees such as blue spruce. Given the number and area of defoliated blue spruce I have been seeing, it is likely we will have an outbreak of the Douglas-fir tussock moth sometime within the next two years. Unfortunately, no relationship has been found between the location of the sentinel trees and the forested areas that will be defoliated in the future. In other words, we know that there will likely be an outbreak, but we do not know exactly where it will occur.

Outbreaks of Douglas-fir tussock moth are cyclical, typically occurring every 7 to 14 years. On average, outbreaks last 2 to 4 years. The last outbreak began in 2008 (Figure 1); therefore, we are due for another.

 

Lifecycle of the Douglas-fir tussock moth

The Douglas-fir tussock moth spends the winter months in the egg stage. Eggs are protected in gray, hairy masses that are approximately an inch in size. An egg mass can contain as many as 350 eggs. The eggs will hatch in late May or early June, depending upon temperatures.

The caterpillar (larvae) will be present from June through August. The caterpillars are quite hairy, with two long hairy tufts projecting from the head and the rear end. They also have four dense tufts of hair on their back, called tussocks, which are whitish in coloration with red tips.

The caterpillars pupate in July-August. Cocoons are grayish-brown, about one inch in size, and can be found on the foliage and trunk of trees as well as in the understory.

The pupae develop into moths and begin emerging in late July. They will continue to be active through November. The females are gray-brown, with large abdomens and are wingless. The males have gray-brown forewings and reddish-brown hind wings. They also have large, feathery antennae.

 

Damage: What to look for

The larvae feed on new needles in the upper crown first. These needles will turn an orangish-brown color (Figure 2). Overtime, the caterpillars will disperse to the lower crown and begin defoliating needles there. The larvae will feed on both new and old needles, sometimes completely defoliating the tree.

trees defoliated by the Douglas-fir tussock moth
Figure 2. Left: Ornamental blue spruce defoliated by the Douglas-fir tussock moth. Center: Ornamental blue spruce and white fir defoliated by the Douglas-fir tussock moth. Right: Close-up of blue spruce defoliation by the Douglas-fir tussock moth. Photos: Melissa Fischer/DNR.

In addition to defoliation, you may find the moth in one of its life stages, depending upon the time of year. Another thing to look for is silk and/or frass ( poop) on the branches (Figure 3).

Signs of Douglas-fir tussock moth
Figure 3. Left: Douglas-fir tussock moth caterpillars feeding on blue spruce foliage. Right: Silk and frass (poop) produced by the Douglas-fir tussock moth. Photos: Melissa Fischer/DNR.

Management

Defoliation by the Douglas-fir tussock moth can cause top and branch kill, which can lead to reduced vigor and growth loss. This can increase susceptibility to bark beetle attack or infection by diseases. Complete defoliation or several years in a row of defoliation can lead to mortality.

Douglas-fir tussock moth is usually controlled over time by natural enemies such as predators, parasites, viruses, cold temperatures, and/ or starvation (eating themselves out of house and home), but can also be managed through use of insecticide treatments.

Bacillus thuringiensis var. kurstaki (Bt) is an insecticide that is specific to Lepidoptera larvae. Its specificity is advantageous because it does not affect other insects, such as the natural enemies that help reduce populations. Because Bt is specific to the larval stage, it would have to be applied when the Douglas-fir tussock moth is in the caterpillar stage.

In forested settings, severe damage can be prevented through thinning. It would be best to remove host trees (Douglas-fir, grand fir, Engelmann spruce) and favor the retention of non-host trees (ponderosa pine, western larch, lodgepole pine) thereby reducing the amount of food available. Additionally, thinning breaks the crown continuity within a stand, so that when the caterpillars disperse, many will fall to the ground and dessicate or be eaten by passing birds.

If you think you may have a sentinel tree on your property, I would love to know about it! Feel free to contact me via Melissa.Fischer@dnr.wa.gov.

By Melissa Fischer, forest health specialist, Washington State Department of Natural Resources, Northeast Region, melissa.fischer@dnr.wa.gov 

Potential for Douglas-fir Beetle Outbreaks in Eastern Washington

Douglas fir killed by bark beetle
Beetle damage in stand of Douglas fir. Photo: Kenneth E. Gibson, USDA Forest Service, Bugwood.org

Several windthrow events in 2015 have paved the way for a potential outbreak of Douglas-fir beetle in areas of eastern Washington this spring (2017).

Douglas-fir beetle egg and larval tunnels
Characteristic pattern of Douglas-fir beetle egg and larval tunnels. Photo courtesy of Oregon Department of Forestry.

The Douglas-fir beetle is a bark beetle that normally breeds in felled, injured, windthrown or root-diseased Douglas-fir. It may also attack western larch, but can only produce brood in downed trees. At outbreak levels, this bark beetle can attack and kill large diameter, healthy Douglas-fir. Outbreaks tend to occur after extensive windthrow events such as was seen in 2015. Outbreaks may also occur after defoliation events, fire and extended drought. Dense stands surrounding areas where windthrow, defoliation, fire and drought events have occurred may be at high risk for an outbreak, particularly if those stands contain a 50 percent or more component of Douglas-fir that are greater than 120 years of age and larger than 14 inches DBH (DBH = diameter at breast height; diameter of a tree bole 4.5 feet from the base).

The Douglas-fir beetle has one generation a year. Brood that developed through 2016 will pupate and emerge as adults this spring. Once emerged, they will begin attacking standing trees surrounding the windthrow, as the windthow is no longer habitable for them.

What can be done?

The best approach to prevent an outbreak this spring is to salvage any large diameter Douglas-fir or western larch that were downed by the storms prior to the adult beetle flight, which should occur in April, depending on temperatures. Windthrown trees can also be burned or chipped on site if salvage is not an option. Time is running out; if you find you cannot take care of this material, the use of the anti-aggregate pheromone MCH is another option.

A pheromone is a chemical released by bark beetles that is used to affect the behavior of other beetles of the same species. Aggregating pheromones attract beetles, while anti-aggregates repel them. A bark beetle might use an anti-aggregate to prevent overcrowding within a tree. An anti-aggregate basically tells other beetles that there is no room for additional inhabitants in the tree.

MCH bubble capsule stapled to a tree
MCH bubble capsule stapled to a tree. Photo: US Forest Service.

The Douglas fir-beetle naturally produces an anti-aggregate to repel others. A synthetic version of this anti-aggregate, MCH, has been produced and is available for purchase through several online companies. MCH comes in a “bubble capsule” and can be used to protect individual live, high-value Douglas-fir or even an entire stand. For individual tree protection, two bubble capsules can be stapled on either side of a Douglas-fir bole at approximately 6-8 feet from the ground for a tree less than 24 inches DBH. Four bubble capsules should be used for Douglas-fir larger than 24 inches DBH. To protect a stand of Douglas-fir, 30 bubble caps per acre can be evenly placed through the stand.

MCH costs approximately $2.50 per capsule and should be hung prior to the beetle flight in April. It is advisable to contact your local forest health specialist if you are considering this method of management. Additional information about this method can be found in the free publication, “Using MCH to protect trees and stands from Douglas-fir beetle infestation,” published by the US Forest Service.

By Melissa Joy Fischer, forest health specialist, Washington State Department of Natural Resources, melissa.fischer@dnr.wa.gov

 

I Hear Bugs Chewing the Wood Inside my Trees!

ugphotos1-3
TOP: Figure 1. Example of a longhorned beetle: spotted pine sawyer (Monochamus clamator) Photo: Richard C. Hoyer, Bugguide.net MIDDLE: Example of a metallic wood borer: Golden Buprestid (Buprestis aurulenta) Photo: Melissa Fischer/DNR BOTTOM: Figure 3. Example of a woodwasp: Sirex nigricornis Photo: Schiff et al. 2006

I hear bugs chewing the wood inside my trees!

Many land managers have contacted me in a panic saying that they could hear bark beetles feeding in their trees. Although bark beetles may be present in those trees what they were likely hearing is wood borer activity. Wood borers tend to be much larger than bark beetles and are, therefore, more likely to be heard chewing away inside trees.

While bark beetles feed solely on a tree’s phloem, wood borers feed on sapwood and heartwood as well as phloem. Native wood borers attack stressed, dying, or dead trees; there are very few native species that actually kill trees.

Wood borers are attracted to volatile gases released by dead or dying trees and lay their eggs under the bark of these trees. Once the larvae hatch, they begin feeding on the inner bark and then tunnel into the wood. The larvae are white, legless grubs and can be quite large. They are valued as a food source by woodpeckers (they make great fishing bait too!) and woodpecker activity is often seen on trees that contain wood borers. The tunnels produced by larval feeding activity have a random pattern and increase in size as the larvae grow.

Frass (beetle poop) is likely to be present within the tunnels. Unlike bark beetle frass, which is fine and reddish in coloration, wood borer frass tends to look more like shredded wheat and is white in color. When wood borers develop into adults, they emerge from trees and leave exit holes that are typically quite a bit larger than those left by bark beetles.

Wood borers play an important ecological role by introducing wood decaying organisms into dead and dying trees which, in turn, helps to speed nutrient cycling. Typically, no management is necessary for native wood borers in a forested setting. Wood borers can damage lumber, but damage is unlikely to occur if the wood has been treated.

Types of Wood Borers

bugphotos4-6
TOP: Figure 4. Asian longhorned beetle Photo: Joe Boggs, Bugwood.org MIDDLE: Figure 5. Citrus longhorned beetle Photo: Art Wagner/Forestry Images. BOTTOM: Figure 6. Emerald ash borer. Photo: Marianne Prue/Bugwood.org

There are three common wood borer families; Cerambycidae, Buprestidae, and Siricidae. The family Cerambycidae, often called longhorned beetles (adults) or roundheaded wood borers (larvae), includes many species. Adults can range in size from ¼ to 2 ½ inches in length. Adults, particularly the males, have long antennae, hence the name longhorned beetle (Figure 1).

The family Buprestidae are commonly known as metallic (adults) or flatheaded (larvae) wood borers. Similar to longhorned beetles, there are many species, and adults may be ¼ to 2 ½ inches in length. Metallic wood borers have small antennae and some are very beautiful, with iridescent or metallic coloration somewhere on the body (Figure 2).

Flatheaded woodborer larvae can be differentiated from roundheaded wood borer larvae in they have a flattened and broadened area beneath the head (thorax) that gives the appearance of a flat head. Rather than the round exit holes left by roundheaded wood borers, flatheaded wood borers leave D-shaped exit holes.

The family Siricidae, often called woodwasps or horntails, are in the order Hymenoptera (i.e., wasps), unlike Cerambycidae and Buprestidae which are in the order Coleoptera (i.e., beetles). Adults may be ½ to 1 ½ inches in length and have a short hornlike process at the end of their bodies. Females have an additional stinger-like ovipositor which is used to oviposit eggs under the bark of trees (Figure 3).

Woodwasp adults can be distinguished from common wasps in that they have thick waists and neither males nor females can actually sting. Woodwasp larvae look similar to roundheaded wood borers but have a small spine at the end of the body. Woodwasps are particularly attracted to fire damaged trees and all except one western species feeds on conifers.

Although native wood borers typically attack stressed, dying and dead trees, several invasive species have been introduced into the United States that are incredibly damaging. The Asian longhorned borer (Anoplophora glabripennis) was introduced into the eastern United States in the early 1990’s. The Asian longhorned beetle feeds on many deciduous species (birch, horse chestnut, poplar, willow, elm and ash), but maples are one of its favorites.

This species has killed thousands of trees in New York and Chicago. Adults are large, 1 to 1 ½ inches long, and have wings that are shining black with irregular splotches of white. The antennae have bands of black and gray and the feet and legs have slate-blue “hairs” (Figure 4). This species can be confused with another invasive, the citrus longhorned beetle (Anoplophora chinensis, Figure 5).

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TOP: Figure 7. The native Prasinalia cuneata. Photo: William Ericson, Bugguide.net. BOTTOM: Figure 8. Sirex woodwasp (Sirex noctilio) female on the left and male on the right. Photo: http://www.sciencephoto.com

The emerald ash borer (Agrilus planipennis) is an invasive metallic-green wood borer (Figure 6) currently found in 30 states. The emerald ash borer attacks ash trees and has killed hundreds of millions of ash in North America. If you have seen rectangular purple traps hanging in trees alongside the road, these traps are being used to monitor for the emerald ash borer, which is attracted to this particular color. The emerald ash borer may be confused with many native metallic wood borer species, such as Prasinalia cuneata (Figure 7).

The European woodwasp (Sirex noctilio, Figure 8) has been accidently introduced into the eastern U.S. as well. This species attacks and kills living pines. Similar to the emerald ash borer, this species may be easily confused with native species.

Reports from citizens help scientists track the spread of these pests. To report a potential invasive species in Washington state, take a picture if possible, and contact the Washington Invasive Species Council.

By Melissa Fischer, DNR landowner assistance/stewardship forester, melissa.fischer@dnr.wa.gov 

References: