United States 

Department o 

Agriculture 

Forest 

Service 

Northern

Region 

200 East Broadway 

P.O. Box 7669 

Missoula, MT 59807 

Report 04-3 February 2004

SHELDON FLATS THINNING AND ENGRAVER BEETLE TRAPPING 

LIBBY RANGER DISTRICT, 1997-1998 

A Case Study 

Ken Gibson1 and Anne Weber2

Introduction

During 1996, personnel from Libby Ranger 

District, Kootenai National Forest, began 

proposing a thinning/fire-hazard reduction 

project in the Sheldon Flats area, north of Libby, 

Montana. There, home development in the 

"forest/urban interface" had resulted in the need 

to address stand structure, forest health and fire 

potential. The area, approximately 1,200 acres 

in size, was comprised of predominantly secondgrowth ponderosa pine, about 65-70 years old. 

In parts of the area, there were varying amounts 

of western larch, Douglas-fir, and lodgepole 

pine; but ponderosa pine was the dominant tree 

species throughout. Tree diameters ranged 

from 6-14 inches, with most in the 10- to 12-inch 

class. 

Implemented on about 800 of the 1,200 acres, 

the primary purpose of the proposed action was 

to reduce fuel loading and fire hazard in a twoentry commercial thin. Half of the area was 

treated during FY97, the other half in FY98. 

---------------------------------------------------------------- 1 Forest Health Protection, Missoula, MT 2

Libby Ranger District, Kootenai National Forest 

Originally, there were several hundred trees per 

acre and basal area averaged around 120 

square feet per acre. Treatments ultimately 

reduced stocking to about 60 trees, and 

approximately 60 square feet basal area, per 

acre. Healthy, vigorous ponderosa pine was 

favored for retention during thinning; however, 

large-diameter trees of other species (Douglasfir and western larch) were left as well. 

Understory vegetation less than 3 inches 

diameter at breast height (d.b.h) was later 

slashed, and future treatments included shortinterval underburns, which developed a more 

naturally appearing, open-grown stand of largediameter trees. 

In addition to fire-hazard reduction, another 

incentive for the project was to reduce future 

threats from several bark beetle species, among

them, mountain pine beetle (Dendroctonus 

ponderosae Hopkins), western pine beetle (D. 

brevicomis LeConte) and pine engravers (Ips 

pini [Say]). Mountain pine beetle populations 

are periodically high in that area and are always 
a threat to over-stocked, second-growth 

ponderosa pine stands when they reach 

average diameters exceeding about 10 inches, 

and basal area stocking greater than 150 square 

feet per acre. Western pine beetles can also be

damaging in densely stocked ponderosa pine 

stands during times of unusually dry spring and 

summer weather. In addition, top-killing or 

whole-tree mortality, attributable to engraver 

beetles, is always a concern when partial cutting

in ponderosa pine. 

Implementation of the thinning project began in 

winter 1997-98. Trees removed were whole 

trees skidded to landings where tops and limbs 

were piled. Piles were to be burned in late 

summer/early fall, 1998. Knowing the potential 

for engraver beetle build-ups in slash piles, and 

subsequent tree- or top-killing was great; district 

personnel elected to carry out ameliorating 

actions, in the form of pheromone-baited funnel 

traps during late spring and early summer, 1998. 

Following is a review of pine engraver life cycle 

and damage potential, as described in Forest 

Insect and Disease Leaflet #122, "Pine 

Engraver, Ips pini (Say), in the Western United 

States" (Kegley, et al. 1997). Such an 

examination might be helpful in more fully 

understanding how beetles may affect 

management decisions and why trapping 

alternatives were selected for Sheldon Flats. 

Engraver Beetle Life Cycle and Ecology

Attacks are initiated by male beetles which bore 

into the inner bark and excavate a nuptial 

chamber. Pheromone attractants released by 

the male attract one to seven females, though 

typically two or three. After mating, each female 

constructs a tunnel or "egg gallery" in the 

phloem layer. During gallery construction, 

boring dust is pushed to the outside, clearing the 

nuptial chamber and egg galleries. Additional 

males are also attracted to the vicinity of the 

initial attack. The attractant pheromone 

promotes an aggregation of beetles or "mass 

attack." 

A female lays from 30 to 60 eggs along the 

sides of the egg gallery, which usually ranges 

from 4 to 7 inches long. Eggs hatch within 4 to 

14 days, and larvae mine laterally from the egg 

gallery for 1 to 2 inches. Larval mines, unlike

parent tunnels, are packed with shredded 

phloem and excrement collectively called 

"frass." Larvae feed for 2-4 weeks and then 

excavate an oval cell at the end of their tunnels 

where pupation occurs. New adults begin to 

appear about 12 days after pupation, or about 

40-55 days after the initial attack by parent 

beetles. When mature, new adults bore through 

the bark and emerge to make new attacks. This

second flight occurs, in our part of Montana, 

about mid-June. That is the flight most 

responsible for mid-summer standing-tree 

mortality. Brood from that generation emerge 

later in the summer—typically during August, 

and it is during this period that large numbers of 

beetles may infest living trees during "feeding" 

attacks. During this time, they mine extensive 

maze-like galleries under the bark without 

producing brood. Occasionally these feeding 

attacks may result in tree mortality.

Beetles spend the winter almost exclusively in 

the adult stage, except in warmer, drier areas 

where some older larvae and pupae may 

overwinter. Adults overwinter under the bark of 

infested trees and slash or in duff and litter on 

the forest floor. 

In most parts of the beetle's range, two or three 

generations per year are common. The first 

flight usually begins in April or May when daily 

maximum temperatures reach 60-70 degrees. 

As overwintering beetles become active, they 

infest fresh slash or trees damaged by wind or 

snow. This generation normally does not 

successfully attack standing green trees. 

However, populations can build up in slash with 

subsequent generations attacking and killing live 

trees, although if new slash is available, it will be 

infested first.

Predicting Outbreaks

The percentage of normal precipitation between 

April and July may be used to predict the 

intensity of pine engraver outbreaks later in the 

season. If precipitation is 75 percent of normal 

or less, moderate to heavy tree mortality may be

expected in overstocked, second-growth 

ponderosa pine stands. Outbreaks are usually 

of short duration, seldom lasting more than one 

season. During extreme droughty conditions, 

damage may continue for 2 to 3 years. 

2 
b. Where slash disposal is impractical, 

lopping into smaller pieces and scattering it into 

openings is effective. Reducing the size and 

exposing the slash to direct sunlight dries it 

faster making it less suitable for beetle 

development. 

Minimizing Tree Mortality

The key to preventing tree damage is the 

promotion of healthy forests. Trees in thinned, 

vigorous stands are infrequently colonized by 

pine engraver beetles. During drought years, 

maintaining stand vigor is even more important. 

Stands in which basal area has been reduced to

80-100 square feet per acre have been found to 

be less susceptible to beetle attack. 

c. When beetle populations in slash 

constitute a threat, creating a continuous supply 

of fresh slash during the flight period of 

emerging adults will generally attract beetles, 

keeping them out of standing green trees. This 

technique is known as providing a "green chain." 

New slash should be produced just as beetles 

enter the pupal stage. Once started, this 

technique should be continued for each 

generation that season.

Most pine engraver problems are associated

with disturbances such as windthrow and snow 

breakage, drought in spring and early summer, 

logging, fires, road construction, housing 

development or other human activities. Pine 

slash or weakened trees created by these 

disturbances attract beetles and provide ideal 

conditions for population buildup and 

subsequent tree killing. 

An alternative to this method is the creation of 

very large slash piles in the spring before initial 

beetle flight. If piles are big enough, interior 

pieces will not dry before beetles from the initial 

generation emerge. Emerging beetles are 

attracted deeper into the pile, keeping them out 

of standing trees. Piles should be at least 20 

feet wide and 10 feet deep, and distributed 

throughout the treated area. This method has 

been used successfully in the northern portion of

the beetle's range (Knopf 1982). 

Because pine engraver beetles overwinter as 

adults and normally only infest fresh slash when 

they emerge in the spring, logging slash created 

from early winter through late spring can be 

especially hazardous by providing large 

amounts of breeding material. Slash should not 

be created during this period unless it can be 

treated prior to beetle emergence. 

The optimum period for logging activity in 

ponderosa pine is late summer to early winter. 

Slash created at this time will usually dry 

sufficiently to be unsuitable for pine engravers 

by the following spring. Slash covered by early 

snows; however, may still be fresh enough to 

attract beetles in the spring. Creating slash from

about January through July, increases the 

likelihood of subsequent tree killing. When it is 

not practical to avoid creating slash during highrisk months, several management practices can

be used to help minimize potential impacts: 

d. During logging, felling trees into openings 

and using established skid trails to avoid 

damaging the residual stand are good practices 

to reduce pine engraver attacks on the 

remaining trees. Trees whose roots are 

exposed or disturbed, and those with large 

patches of bark torn off should be removed. 

e. An additional method, the one chosen for 

Sheldon Flats, entails the use of pheromonebaited funnel traps to capture beetles emerging 

from small, infested slash piles. Traps are hung 

around infested piles, typically during the latter 

part of May (in Montana and northern Idaho), 

and will attract emerging beetles into traps, 

keeping them from infesting surrounding trees. 

While more labor intensive, this method has 

been used successfully. Still, it should be 

considered secondary to proper slash treatment. 

a. Prompt slash disposal. Bulldozer 

trampling or chipping effectively reduces the 

amount of breeding material by decreasing the 

size of logging debris and by removing and 

drying the bark. Burning slash while still green 

also destroys potential brood sites. When 

burning slash, however, avoid scorching 

standing trees. Fire injury makes them more 

attractive to various species of bark- and woodboring insects. When chipping slash, we have 

learned it is best not to deposit chips in host 

stands during beetle flight periods. 

Sheldon Flats Thinning Project

Initial thinning was completed during late winterearly spring, 1998. Several hundred acres were 

thinned, throughout which logging residues were

3 
piled into 43 piles. Slash piles varied from 10 

feet to 100 feet in diameter and 6 to 10 feet 

deep. Because slash piles varied as much as 

they did, and there was a desire to lose no leave 

trees, if at all possible, we decided to place 

pheromone traps around each pile, after they 

were infested. We did not hang traps prior to 

beetle flight, in an attempt to prevent slash pile 

infestation. We had tried such a technique 

several years earlier, with poor results (Gibson, 

unpublished office data).

We do not have the precise date recorded when 

initial attacks began; but because spring 1998 

was atypically warm and dry; attacks may have 

begun in early- to mid-April. 

Engraver Beetle Population-Reduction 

Trapping 

By the end of beetle flight period, all slash piles 

were heavily infested by engraver beetles. 

While some piles were probably large enough to 

contain beetles of succeeding generations, 

pheromone-baited funnel traps were hung 

around each pile to attract emerging beetles and 

help assure no leave trees were attacked during 

subsequent dispersal flights. 

A similar use of traps, but used in an area where 

wind, ice, and snow had broken tops and limbs 

from mature ponderosa pine over a large area 

during winter 1996-97, was described by Kegley 

(1998). In that situation, broken and winddeposited material was not cleared from the 

area prior to beetle flight in spring 1997. It was 

subsequently infested heavily by engraver 

beetles. Because the infested material could not

be removed before beetle emergence, traps 

were hung throughout the area before 

emergence began in spring 1997. Many beetles 

were collected and no green-tree mortality was 

observed anywhere in the area (Kegley 1998). 

In the Sheldon Flats area, traps—3 to 4 around 

each pile—were hung in early May; after initial 

flights were over, but before brood development 

was completed. Traps were standard 8-funnel, 

Lindgren traps, baited with the commercially 

available I. pini lure—lanierone and ipsdienol. 

Traps were hung on tripods constructed from 

iron, concrete-reinforcing rods, cut to lengths of 

about 10 feet. 

Traps were emptied weekly, from May 25 to 

August 4 when trap catches had declined 

markedly. Traps were removed and slash piles 

were subsequently burned. Around 43 slash 

piles, we hung 128 traps. First beetles were 

collected May 25, peak flight occurred about 

July 7, and last beetles were collected on 

August 4 (though flights may not have been 

entirely over). In total, an estimated 54,200 

beetles were collected—an average of more 

than 400 per trap (figure 1). 

4 
Figure 1. ENGRAVER BEETLE TRAP CATCHES--19981 

5/25 6/1 6/8 6/14 6/21 6/28 7/7 7/14 7/21 7/28 8/4

Collection Date, 1998

0

2000

4000

6000

8000

10000

12000

Beetles 

Trappe

d

1 Trap catches from 128 traps, surrounding 43 slash piles. Estimated beetles: 54,200; 

 Peak Flight: July 7-14. 

reduce engraver beetle-caused damage during 

mid-summer flights. And because a portion of 

our success may have been due to the size of 

slash piles created in the area, it likewise 

supports Knopf's observations of more than 20 

years ago (Knopf 1982). 

Conclusion 

Through 1998, we found no engraver beetleattacked trees in the Sheldon Flats area. 

Because it seems likely the 54,000 beetles 

trapped would have infested tops or trees had 

they not been attracted to traps, we considered 

the trapping effort successful. Subsequent 

aerial and ground surveys throughout that part 

of the district revealed only endemic-level tree 

mortality associated with drought-related 

conditions prevalent in that area during the 

ensuing several years. All indications over the 

period since trapping was completed suggest 

trapping successfully prevented engraver beetlecaused mortality in the treatment area. 

Though trap installation and monitoring was 

labor-intensive, and similar projects would have 

to be assessed on their own unique conditions; 

the desire to preserve and maintain as many 

"leave" trees as possible justified that expense 

in Sheldon Flats. Whether such a procedure 

should be considered "operational," appropriate 

for another time and place, is conjectural. It 

does; however, seem to have been a prudent 

choice for Sheldon Flats. 

This project was essentially a “case study”—

operational more than experimental—and 

therefore not particularly amenable to statistical 

analysis. However, it did provide additional 

evidence in support of Kegley's earlier work 

(1998), relative to the use of pheromone traps to 

References

Kegley, S. 1998. Using pheromone traps to 

protect pine stands from pine engraver (Ips 

pini [Say]) infestation. USDA For. Serv. 

North. Reg. FHP Report 98-3. 3pp.

5 
6 

Kegley, S.J., R.L. Livingston, and K.E. Gibson. 

1997. Pine engraver, Ips pini (Say), in the 

western United States. USDA For. Serv. 

Forest and Insect Disease Leaflet #122. 

8pp. 

Knopf, J.A.E. 1982. Attraction and containment 

of Ips beetles by large slash piles. USDA 

For. Serv. Intermtn. Reg. FPM Report 82-8. 

4pp.