Bark Beetle Info

The story of the beetles killing pine and fir trees in the San Bernardino Mountains is complex. Insects
that attack plants have always been part of our forest ecosystem. When healthy, most trees' natural
defenses can successfully combat these insect attacks, but when they are stressed these attacks can
prove difficult to fend off.

One of the most significant contributing stress factors threatening the forest's health is high tree
density. How did the forest become so dense? Many years ago, our society adopted two dictums: "All
tree cutting is bad," and "All fires are bad." This was borne of well intentioned but uninformed people
basing decisions on emotions rather than hard science.

The result is a forest density on well over the 40 - 50 trees per acre nature can support. Tree surveys
conducted in the San Bernardino mountains often shows a density of over 200 trees per acre, and
within the urban-forest interface frequently over 400 trees per acre. Mother Nature simply does not
provide enough available resources for this amount of trees. We had unknowingly created a time
bomb, and the fuse was waiting to be lit. The match was a four year drought.

Mountain residents, by and large, now know that the combination of extremely high tree stand density,
opportunistic insects, long periods of warm weather and drought set the forest up for disaster. Far too
little rain and snow stressed the trees, dropping their tree vigor index (TVI, a measure of tree health).
Akin to our immune system, a lowered TVI allowed insects that may have otherwise been expelled by
a healthy tree during an attack to succeed. The sheer number of stressed trees resulted in huge
numbers of beetles, which exacerbated the problem: More stressed trees, more beetles. So many
beetles, in fact, that very healthy trees (with high TVI) often succumbed to beetle attacks.

There are actually three beetles guilty of the lion's share of tree mortality in the San Bernardino
Mountains. They are the western pine beetle, the ipps beetle, and the turpentine beetle. Of these, the
western pine beetle has been quite destructive. Each has their own characteristics.

The western pine beetle, Dendroctonus brevicomis, primarily attacks Douglas firs, and ponderosa
and coulter pines. Initial attacks are midway up the tree, but the first sign of attack may often be frass
(wood dust from boring into the bark) and predaceous checkered beetles seen at eye level scurrying
over the bark in search of western pine beetle prey.

Attacking adult beetles carry spores of a blue-staining fungus, Ceratocystis minor, that hitchs a ride
into the tree in special pouch-like structures in their heads. As the beetles chew their way through the
bark, the spores of this wilt-causing fungus dislodge and begin to germinate. In trees attacked in early
or midsummer, it takes only a few weeks for the fungus to invade and block the conductive vessels of
the inner bark and sapwood. Once the vessels are blocked, the tree is "choked" of water and
nutrients, the foliage begins to fade, first to a pale green and then to yellow and brown. Depending on
the season, trees can succumb quickly or last until the following spring.

The fungus stains the inner heart wood blue, but does not effect its strength, as some would have you
believe. Western pine beetles pass through the egg, larval, pupal, and adult stages during a life cycle
that varies in length from about 2 months in warm weather to 10 months in cool weather.
All stages are completed beneath or in the bark of infested trees, except for a brief period when the
adults fly, sometimes for many miles, to find new trees to attack.

The red turpentine beetle, Dendroctonus valens, measuring almost ½ inch in length. Adults are
reddish brown in color. An attack from red turpentine beetles does not always result in death for the
host tree, but when death does come from such attacks, it results from a disruption of nutrient and
water transfer up the tree's vascular system. Attacks are generally confined to the host's lower bole
(trunk) and are easily recognized based on the large pitch masses produced on the outer bark. These
pitch masses vary in size, texture and color, depending on the amount of bark and frass embedded in
the resin, but typically are about one inch in diameter. Eggs are laid along the edges of short,
irregular galleries. Larvae feed en masse, each group excavating a cavity under the bark.

The ipps beetle primarily attacks the upper portions of white firs and lodgepole pines. Death does
not always result from a successful ipps attack, and many mountain residents have probably seen
otherwise healthy looking firs and lodgepole pines with bare tops. Should the ipps beetle manage to
kill too much of the upper photosynthesizing canopy, say over 15% of the canopy, the tree may be too
stressed to survive.

Management and Prevention Thinning stands of trees to healthy levels is the best solution to
raise the remaining trees' TVI and enable them to survive a variety of threats. Watering with a
soaker hose just inside the canopy's drip edge during late spring and early summer may help as well,
but is no guarantee. Unfortunately, there is virtually nothing you can do to kill beetles once they have
bored their way into your tree. Slick salesmen may try to sell you systemic tree inoculation and soil
injection solutions, but none have been shown to be effective for these bugs. However, there are two
topically applied products available that will kill these beetles as they enter or exit trees, but special
equipment is needed to spray large trees. Click here to contact Aaron Scullin, a professional
licensed pesticide applicator. He is also expert at dealing with oak leaf rollers, as well as fertilizing
and soil analysis. Want healthy trees? Contact Aaron today.