Quick Facts...
- Ips is a common group of bark beetles that infests pine and spruce
trees.
- Ips beetles rarely attack healthy trees. Most problems with ips occur
to newly transplanted pines or when plants are under stress.
- Several generations of ips can occur in a season.
- There are 11 species of ips beetles found in Colorado.
Ips beetles, sometimes known as “engraver beetles,” are bark
beetles that damage pine and spruce trees. They develop under the bark
and produce girdling tunnels that can cause dieback and kill trees. Eleven
species of ips beetles occur in Colorado (see Table 1 below).
| Table 1. Common ips beetles (Ips species) affecting
pines and spruce in Colorado. |
| Species |
Hosts |
Comments |
| Ips hunteri |
Spruce |
This is a common species affecting Colorado blue spruce
in landscape settings. Upper portions of the tree are typically infested
first. |
| Ips pilifrons |
Spruce |
A forest species often called the “spruce ips”;
tends to infest the upper part of fallen trunks. |
| Ips pini |
Ponderosa, lodgepole |
The most common species associated with other pines
pines in Colorado. |
| Ips knausi |
Ponderosa pine |
Common at base of trunk and in fresh stumps. |
| Ips calligraphus |
Ponderosa pine |
Largest ips species in Colorado; often in main trunk. |
| Ips confusus |
Piñon, rarely other pines |
Periodically kills piñons over large areas. |
| Ips latidens |
3- and 5-needled pines |
|
| Ips borealis |
Engelmann spruce |
|
| Ips integer |
primarily Ponderosa pine |
|
| Ips woodi |
Limber pine |
|
| Ips mexicanus |
Lodgepole and limber
pines |
|
Ips beetles are generally not considered as destructive or aggressive
as bark beetles in the genus Dendroctonus (mountain pine beetle, spruce
beetle, Douglas-fir beetle). Normally ips beetles limit their attacks
to trees that are in decline due to root injuries, wounding, or other
stresses. However, under widespread conditions which allow improved survival
and large population build-ups, ips beetles are a considerable threat
to living trees. Two factors that recently contributed to ips beetle problems
in Colorado include: prolonged drought stress; and the creation of freshly-cut
wood (which is a prefered breeding site) from forest homeowner efforts
to reduce wildfire hazards.
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 |
| Figure 1: Adult Dendroctonus (left)
versus Ips (right). Note gradually curved wing of Dendroctonus.
Actual size of Dendroctonus from 1/8 to 1/3 inch, Ips
1/8 to 3/8 inch. |
Ips beetles are small (1/8 to 3/8 inch long), reddish-brown to black
beetles. They have a pronounced cavity at the rear end, which is lined
with three to six pairs of tooth-like spines, depending on the species.
The latter feature distinguishes them from other bark beetles (see Figure
1).
Symptoms of Ips Beetle Injury
 |
|
Top dieback of spruce from drought
stress and ips attack.
|
 |
|
Storing cut firewood near susceptible
trees greatly increases the risk of ips beetle attack.
|
As adult ips beetles enter trees and tunnel, a yellowish- or reddish-brown
boring dust is produced and accumulates in bark crevices or around the
base of the tree. When the larval tunnel, affected parts of the tree discolor
(“fade”) and die.
These symptoms may be limited to parts of the tree, such as a single
branch or the top. However unlike mountain pine beetle, infestation by
ips beetles does not necessarily mean the whole tree will die, but over
time, attacks may progress as later generations “fill” the tree
and then ultimately the host can die.
Small round holes in the bark of infested trees indicate the beetles
have completed development in that part of the tree and the adults have
exited. The presence of these holes peppering the bark show the beetles
have moved to another part of the same tree or to neighboring trees.
Woodpeckers are common predators of ips beetles. Their presence may also
indicate bark beetle activity. Woodpeckers often remove the tree bark
in an effort to obtain this food source. This habit results in ragged
holes or patches of missing bark on the tree.
Generalized Life History
Adults overwinter under the bark or in surrounding litter at the tree base.
They begin to attack weakened trees in the spring. Initially the male
enters the tree, constructs a cavity under the bark known as the “nuptial
chamber.” Females are attracted to the tree by chemicals (pheromones)
produced by the male.
After mating, females (usually three) excavate egg galleries off the
central chamber. The tunnels produced by the adults appear as a “Y”-
or “H”- shaped pattern. These galleries are mostly free of boring
dust, which is pushed out of the entrance hole as the adult beetles work.
These “cleared out” galleries have a different appearance than
the debris-filled galleries of Dendroctonus. Eggs are laid along the gallery
and young larvae soon hatch and begin tunneling smaller lateral galleries
that lightly etch the sapwood. They are small grubs, about 1/4 inch long
when mature, white to dirty gray, legless, with dark heads. In Colorado,
two to four generations of these beetles usually develop per year.
 |
|
Boring dust at the base of a pine
tree. Reddish boring dust is caused by ips beetles. The whitish
dust is from ambrosia bark beetles.
|
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|
Tunneling by Ips hunteri
in blue spruce.
|
Management
To prevent ips beetle attacks, use practices that promote vigorous tree
growth. Properly siting trees in landscape plantings is important to allow
optimal growing conditions as the tree matures. Adequate – but not
excessive – water may be needed. Root injuries caused by mechanical
damage, compaction, or disease should be avoided.
Freshly-cut material that results from pruning or thinning practices
(called “slash”) should be removed from the vicinity of valuable
trees. Never stack green or infested coniferous wood next to living coniferous
trees. Such green woody material should be chipped or treated so that
the inner bark area is destroyed. Ips larvae will not survive standard
chipping or debarking treatments. Other treatments could include scattering
(as opposed to piling) slash to promote rapid drying.
Trees at risk of ips attack include newly transplanted trees, trees suffering
root injuries from construction, and trees surrounded by large breeding
populations of ips beetles. These types of trees can benefit from preventive
insecticide applications.
Insecticides are used as drenching preventive sprays on the trunks and
larger branches. These insecticides need to be applied prior to adult
beetle infestation. (Remember that overwintering beetles begin emerging
in spring as soon as daytime temperatures consistently reach 50 F to 60
F.) However, timing can be difficult to determine since ips beetles can
have multiple, overlapping generations and life cycles. Adults have been
observed entering trees during warm days as early as late-February on
through November. Because of this extended activity, two treatments (early
spring and summer) may be needed to protect trees during high-risk conditions.
Insecticides used to prevent ips include either permethrin, bifenthrin,
or carbaryl (Sevin) as the active ingredient. There are many products
currently on the market containing these active ingredients. Follow the
manufacturer’s recommendation for the proper rate for bark beetle
treatment. Bark beetle applications at the labeled rate should provide
at least three months control of ips beetles.
When a preventively-sprayed tree later dies of beetle attack, it is usually
for one of the following reasons: 1) the tree was sprayed after it was
attacked; 2) the spray was applied at too dilute a rate; 3) the entire
bark surface of the susceptible part of the tree was not sprayed; or 4)
the material wore off and was no longer effective.
Note: Concentrations of insecticides used to control
bark beetles are often considerably greater than those used for insects
on foliage. To avoid needle burning, try to limit the application to the
bark, particularly when using liquid (emulsifiable concentrate) formulations
that have increased risk of causing plant injuries.
Insecticide applications are not needed when ips beetles do not pose
a serious risk to healthy trees. Ips problems are often an issue for a
few years, then lessen naturally to non-threatening levels. This is the
normal condition in Colorado. A rule of thumb when deciding if preventive
treatments are needed is to survey for infested groups of bark beetle-killed
trees (as determined by dead foliage) within sight of the live trees in
question. Also, transplants or recently disturbed trees in natural forest
areas or near other known sources of ips may warrant protection. Tree
value, of course, is always a consideration. There is often more interest
in protecting high-value trees such as those around residences, golf courses,
or in other highly visible settings.
No chemical treatment exists for trees or wood already infested by ips
beetles. In rare cases where it is feasible to reduce the threat to live
trees by killing beetles within infested trees before they exit, treatments
involve bark removal, chipping the wood into small pieces, covering piles
with a double-layer of 6-mil thick clear plastic sealed around the edges
with soil to heat (solarize) the wood, or physical removal of infested
material from the site to an area a mile or more from susceptible trees.
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| Ips confusus pitch tubes on infested pinyon pine trunk. |
Ips pini egg galleries under bark of ponderosa
pine trunk.. |
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