USDA Forest Service RMRS-RN-27. 2005 1

United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

Research Note

RMRS-RN-27

August 2005

Introduction____________________

Knowledge of the emergence and flight period for the 

mountain pine beetle (Dendroctonus ponderosae Hopkins) 

is useful in management efforts to minimize beetle-caused 

tree mortality. Control of mountain pine beetle (MPB) 

populations must be completed before MPB emergence begins (McCambridge 1964). Surveys for newly infested trees 

must wait until emergence is complete if all newly attacked 

trees are to be located.

MPB emergence from ponderosa pine (Pinus ponderosa

Lawson) in Colorado generally corresponds to the following pattern. In ponderosa pine (PP), beetles usually begin 

emerging about July 15 (McCambridge 1964) although 

MPB emergence has started the last week in June. Once 

started, emergence proceeds slowly and erratically for the 

next 20 days (McCambridge 1964). Then MPBs emerge in 

larger numbers with emergence reaching a peak (numbers/

day) around August 20. By the end of August, approximately 90% of the beetles have emerged (McCambridge 

1964). Although this pattern occurs in most years, beetle 

emergence may occasionally begin the first week in July 

and peak by early August if exceptionally warm weather 

occurs during the developmental period (see McCambridge 

1964).

While the emergence period is known when PP is the 

host, little information has been published regarding MPB 

emergence from lodgepole pine (Pinus contorta Douglas) 

in Colorado. Most of our knowledge regarding MPB 

1 Biological Technician, Forestry Technician, and retired Forest 

Entomologist, respectively, Rocky Mountain Research Station, Fort Collins, 

Colorado.

Mountain Pine Beetle Emergence 

From Lodgepole Pine at Different 

Elevations Near Fraser, CO

J. Tishmack,1 S.A. Mata, and J.M. Schmid

Abstract—Mountain pine beetle emergence was studied at 8760 ft, 9200 ft, and 

9900 ft near Fraser, CO. Beetles began emerging at 8760 ft between July 9 and 

July 14 while no beetles emerged at 9200 ft and only one beetle emerged at 9900 ft 

during the same period. Beetle emergence continued at relatively low but fluctuating rates for the next two to three weeks. Peak emergence occurred about August 5 

at 8760 ft, about August 12 at 9200 ft, and from August 12 to 19 at 9900 ft. Beetle 

emergence was complete by September 3. Average numbers of beetles emerging 

ranged from 5 to 256/ft2 of bark per tree with the means for each elevation not significantly different. Attack densities averaged between 6 and 9/ft2

 of bark for the 

three elevations. Population trend ratios were computed for each tree and ranged 

from 0.4 to 32.0. Trend ratios varied substantially among trees but were not significantly different among elevations due to the significant variation among trees. 

The emergence period and population trend ratios are discussed in relation to suppression/survey projects and a stand susceptibility system.

emergence from lodgepole pine (LP) comes from work in 

other Rocky Mountain states and Canada. In British 

Columbia, the beginning and ending of the emergence period varied between 1955 and 1960; the earliest beginning 

was June 16, 1957, and the latest ending was August 20, 

1960 (see Reid 1962). In southeastern British Columbia, 

MPBs emerged between July 14 and August 8 in two consecutive years with peak emergence occurring the last week 

in July (Safranyik and Jahern 1970). In Utah, MPB emergence lasted from July 24 to August 8 in 1974 and from 

July 30 to August 25 in 1975 with peak MPB emergence occurring on July 31 and August 17, respectively (Rasmussen 

1980). In previous work, peak emergence lasted <9 days for 

three consecutive years but dates of emergence were not 

stated (Rasmussen 1974).

MPB populations are currently at epidemic levels in the 

Fraser Valley (Grand County, CO). The 2003 aerial survey 

estimated more than 400,000 infested trees in the county 

(R. Cain 2004, personal communication). Infestations can 

be found from the lowest elevation of LP to near timberline. These populations in the Fraser Valley provided an 

opportunity to study MPB emergence from LP in Colorado. 

We compared MPB emergence periods from infested LP at 

three different elevations, determined average numbers of 

beetles emerging per ft2 of bark, and analyzed population 

trend ratios.

Methods_______________________

Screen emergence cages were attached to MPB-infested 

LP trees at three locations in the southern portion of the 

Fraser Valley, CO, on June 18, 2004. The three locations 

were: (1) about 2 miles west of Fraser on Denver Water 

Board land, elevation = 8760 ft; (2) along the Fool Creek 
2 USDA Forest Service RMRS-RN-27. 2005

road on the Fraser Experimental Forest about 5 miles 

southwest of Fraser, elevation = 9200 ft; and (3) further 

south up Fool Creek road on the Fraser Experimental 

Forest, elevation = 9900 ft. One cage was attached on the 

north side at breast height to each of eight trees at 8760 

ft, each of six trees at 9200 ft, and each of six trees at 9900 

ft elevation. Each cage covered about 2 ft2 of bark surface. 

The north sides were caged because greater densities are 

usually found on that aspect in LP (see Reid 1963) and in 

PP (McCambridge 1964, Negron and others 2001). Cages 

were first checked on June 24, 2004, then weekly beginning on July 9 until September 3, 2004. Numbers of MPBs 

captured in jars attached to the cages were counted and 

recorded for each collection date.

To derive the relationship between MPB emergence and 

calendar date, the number of MPBs collected from all trees 

at each elevation were added together for each collection 

date. The total number for each elevation on a specific date 

was then divided by the number of days since the previous 

collection date. The quotient represented the average number emerging each day since the previous collection date. 

The quotients were plotted on the specific collection dates 

to derive a generalized trend for MPB emergence. The 

specific date for peak emergence at each elevation could 

not be determined because cages were not checked daily. 

However, the time period when peak emergence probably 

occurred was determined and we refer to the periods as 

“peak emergence.”

When MPBs were no longer found in the jars and emergence was considered finished, the cages were removed. 

Within the area covered by each cage, one 6” X 12” bark 

sample (0.5 ft2 of bark) was removed. The number of attacks 

within the sample were counted and recorded. That number was multiplied by 2 to derive the number of attacks per 

ft2. Assuming two beetles (1 male and 1 female) create the 

gallery and brood arising from each attack, the number of 

attacks per ft2 was then multiplied by 2 to derive the number of MPBs creating the attacks in that ft2

 of bark.

A population trend ratio (PTR) was determined for each 

tree at each elevation by dividing the number of MPBs 

emerging per ft2 by the number of MPBs creating the attack densities per ft2

. The number of MPBs emerging per 

ft2 of bark equalled the total number of MPBs emerging in 

each cage during the emergence period divided by 2. The 

number of MPBs creating the attack densities was derived 

as described in the previous paragraph. The PTR is the 

quotient of the number of MPBs emerging per ft2 divided 

by the number of MPBs creating the attack densities. A 

PTR >1 indicates an increasing population while a PTR <1 

indicates a decreasing population.

A multiresponse permutation procedure (MRPP, Mielke 

and Berry 2001) was used to compare emergence profiles 

among elevations. MRPP was also used to compare the total number of beetles emerging per ft2

, attack densities/ft2, 

and PTR among elevations.

Results and Discussion__________

Emergence

No beetles emerged before July 9 at any of the three 

elevations. Between July 9 and July 14, beetles emerged 

from five of the eight trees at 8760 ft, no beetles emerged 

from trees at 9200 ft, and one beetle emerged from one tree 

at 9900 ft (table 1). From July 14 to July 30, the number 

of emerging beetles increased at each elevation with average numbers per tree much greater from trees at 8760 

ft than at either of the higher elevations. The number of 

beetles emerging between July 30 and August 5 increased 

at least five times the number emerging between July 23 

and July 30 at each elevation (table 1). Between August 5 

and August 12, the number of emerging beetles declined 

at 8760 ft but increased at the higher elevations. Between 

August 12 and August 19, the number of emerging beetles 

continued to decline at 8760 ft, declined at 9200 ft, and was 

about equal to the number emerging during the previous 

week at 9900 ft. By August 26, MPB emergence at 8760 

ft declined to 11 beetles during the previous seven days 

while emergence at 9200 ft and 9900 ft also declined but 

was greater than at 8760 ft. During the period of August 

26 to September 2, emergence was essentially complete at 

8760 ft and declined slightly at 9200 and 9900 ft in comparison to the previous collection period. On September 3, 

only one beetle was found at 9200 ft and no beetles at the 

other two elevations, so MPB emergence was considered 

complete (table 1).

As depicted by the average number of MPBs emerging 

per day (figure 1), the emergence profiles differed between 

8760 ft and the other two higher elevations (p <0.05). 

Emergence at the lowest elevation began before emergence 

at the two higher elevations. Peak MPB emergence at 8760 

ft began one week before peak emergence at 9200 and 9900 

ft. Peak emergence lasted about one week at 8760 ft and 

9200 ft but appeared to last about two weeks at 9900 ft. 

Peak emergence over a one week period generally agrees 

with the duration of peak emergence for MPB in LP in 

Utah (see Rasmussen 1974). Although MPBs were still 

emerging at 8760 ft during the August 26-September 2 collection period, their numbers were relatively low compared 

to the numbers emerging at the other two elevations. Thus, 

emergence at 8760 ft may have ended about one week before it terminated at 9200 and 9900 ft.

The general pattern of MPB emergence from LP followed 

the emergence patterns for MPB in PP as determined by 

McCambridge (1964) and Schmid (1972). Once emergence 

began, MPBs emerged at relatively low variable rates for 

two to three weeks. Peak emergence generally occurs over 

a one to two week period after which emergence ceases by 

the end of August or early September.

In the central Rockies, the initiation of MPB emergence 

from LP appears to coincide with the dates at which MPB 

emergence commences in PP (see McCambridge [1964] and 

Schmid [1972]). However, the termination of MPB emergence in LP, at least for 2004, varied with respect to the 

termination of emergence in PP, terminating sooner in 

LP than in PP in Colorado (see McCambridge 1964) and 

in the southern Black Hills (J.M. Schmid, unpublished 

data) but coinciding with the termination of emergence in 

PP in the Black Hills in 1966 and 1967 (see Schmid 1972). 

For 2004, peak MPB emergence from LP at 9200 ft and 

9900 ft coincided with the peak emergence period of midAugust observed by McCambridge (1964) in PP in Colorado 

while peak emergence from 8760 ft was more similar to 

a mid-August date reported by McCambridge (1967). 

Considering the reports by Reid (1962), Rasmussen (1980), 
USDA Forest Service RMRS-RN-27. 2005 3

and McCambridge (1964 and 1967), the MPB emergence 

period and date of peak emergence varies considerably 

from year to year.

Densities of Emerging Beetles

The number of MPBs emerging per ft2 of bark varied 

among trees and elevations (Table 2). The number of MPBs 

emerging per ft2 of bark ranged from 40 to 256 at 8760 ft, 

30 to 213 at 9200 ft, and 5 to 196 at 9900 ft (table 2). The 

number of MPBs emerging from trees at 8760 ft was not 

significantly greater than the number emerging at 9200 

and 9900 ft (p = 0.47).

Table 1—Numbers of emerging MPBs per tree by collection date and location. “No” in the table means that the jars were 

not checked on those trees on that date.

Collection date

July July July July July July Aug Aug Aug Aug Sept Sept

9 14 15 20 23 30 5 12 19 26 2 3

Elevation 8760 ft.

Tree 1 0 4 0 7 12 17 35 2 4 0 0 0

Tree 2 0 37 12 84 31 60 15 18 4 1 2 0

Tree 3 0 9 0 8 10 26 246 52 5 0 0 0

Tree 4 0 4 0 9 0 5 380 100 11 2 1 0

Tree 5 0 4 0 9 0 7 136 60 9 0 1 0

Tree 6 0 No 0 9 0 11 253 99 7 7 2 0

Tree 7 0 No 4 6 7 46 87 21 1 0 1 0

Tree 8 0 No 6 46 22 72 32 2 3 1 0 0

Elevation 9200 ft.

Tree 1 0 0 2 0 0 4 13 62 67 6 8 0

Tree 2 0 0 0 3 1 2 35 183 92 3 2 0

Tree 3 0 0 2 1 1 3 57 279 64 9 10 0

Tree 4 0 0 0 0 1 2 3 30 49 15 12 1

Tree 5 0 0 1 0 1 10 17 22 5 3 2 0

Tree 6 0 0 1 1 2 7 54 48 42 6 4 0

Elevation 9900 ft.

Tree 1 0 0 0 0 1 2 11 119 204 37 19 0

Tree 2 0 0 0 0 1 0 16 166 44 3 9 0

Tree 3 0 0 0 0 1 0 5 40 28 10 5 0

Tree 4 0 1 0 2 0 1 4 20 7 0 1 0

Tree 5 0 0 0 0 0 0 1 38 104 17 20 0

Tree 6 0 0 1 0 0 0 3 2 2 0 2 0

Average number of MPB Emerging

per day per collection period

Figure 1—Average number 

of mountain pine beetles 

emerging per day for three 

elevations for each collection date.

In comparison to MPB densities emerging per ft2 of LP 

from other locations, 75% of the trees in this study had densities generally within the range observed by Reid (1963) 

for LP in British Columbia but 25 percent of the 20 caged 

trees had densities exceeding the largest number recorded 

in Reid’s study.

Attack Densities

MPB attack densities ranged from 2 to 14/ft2 for the 

three elevations. More specifically, attack densities ranged 

from 4 to 8/ft2 at 8760 ft, 6 to 14/ft2 at 9200 ft, and 2 to 8/ft2

at 9900 ft (table 2). The bark sample from the tree with only 
4 USDA Forest Service RMRS-RN-27. 2005

two attacks/ft2 had about 1/3 of the sample devoid of MPB 

galleries. Generally, attack densities averaged between 6 

and 9/ft2 and were not significantly different among elevations (p = 0.55).

MPB attack densities of this magnitude were comparable to attack densities for MPB infestations in LP in 

British Columbia where Reid (1963) found densities averaging from 5.1 to 10.9/ft2

 of bark but ranging from 0 to 21. 

Densities were slightly less than the 9.6 and 10.4 attacks/

ft2 found by Rasmussen (1980) in Utah in 1974 and 1975. 

In comparison to attack densities in PP, attack densities in 

this study were slightly greater than average attack densities found by McCambridge (1967).

Population Trend Ratio (PTR)

The PTRs varied substantially among trees but were not 

distinguishable among elevations (p = 0.57). PTRs ranged 

from 2.5 to 32.0 for trees at 8760 ft, from 1.1 to 13.3 for 

trees at 9200 ft, and from 0.4 to 22.5 for trees at 9900 ft 

(table 2).

If the PTRs for the caged areas are indicative of MPB 

emergence for entire trees and trees attacked in 2004 have 

DBHs and attack densities equal to those observed for 

MPB-attacked trees in 2003, then forest managers expected a substantial increase in the number of MPB-attacked 

trees in 2004 as compared to 2003 unless mortality during 

the flight period was greater than that of previous years. At 

8760 ft, the number of MPB-attacked trees would be more 

than 11 times the number attacked in 2003. Similarly, the 

number of MPB-attacked trees at 9200 ft in 2004 would 

be more than six times the number attacked in 2003 and 

the number at 9900 ft would be more than eight times the 

2003 number.

Management Implications_________

The MPB emergence pattern in LP suggests that control/

suppression projects should be completed or terminated by 

the first week in July. Such efforts could be continued past 

the first week in July but control efficiency would decline 

with each passing day. July 15 should be the cutoff date if 

projects are extended past July 1.

The emergence patterns also suggest that surveys for 

locating newly attacked trees could begin the first week 

in September. Surveys conducted in mid-September would 

expect to locate all of the newly attacked trees and estimates would not be in error because of trees attacked after 

the survey had begun.

In the stand susceptibility rating method of Amman 

and others(1977), the 9500 ft elevation is the threshold 

separating highly susceptible stands from moderately susceptibile stands. This threshold was established because as 

elevation increases, beetle development is retarded which 

increases beetle mortality and thus reduces the MPB population (Amman and others 1977). Based on the PTRs for 

the caged trees at 9900 ft, MPB populations increased 

substantially in 2004 (table 2), which suggests that winter 

temperatures may have been less influential during the 

preceeding year.

Table 2—Number of emerging MPBs per ft2, attack densities per ft2, and population trend ratios per 

tree by location.

Number of MPBs/ft2 Attack densities/ ft2 PTR

Elevation 8760 ft.

Tree 1 40 8 2.5

Tree 2 132 8 8.2

Tree 3 178 8 11.1

Tree 4 256 4 32.0

Tree 5 113 8 7.1

Tree 6 194 6 16.2

Tree 7 86 4 10.8

Tree 8 92 8 5.8

Average 136 6.8 11.7

Elevation 9200 ft.

Tree 1 81 8 5.1

Tree 2 160 6 13.3

Tree 3 213 10 10.6

Tree 4 56 6 4.7

Tree 5 30 14 1.1

Tree 6 83 8 5.2

Average 104 8.7 6.7

Elevation 9900 ft.

Tree 1 196 8 12.3

Tree 2 120 6 10.0

Tree 3 44 8 2.8

Tree 4 18 8 1.1

Tree 5 90 2 22.5

Tree 6 5 6 0.4

Average 79 6.3 8.2
USDA Forest Service RMRS-RN-27. 2005 5

For the MPB in LP, cold hardiness—the ability to survive lethal winter temperatures—begins to develop in 

the fall, reaches a maximum in December, January, and 

February, and begins to decline in late February or early 

March (Wygant 1938). During December thru February 

when maximum cold hardiness is achieved, larval mortality begins at temperatures ≤ -20o

F but only about 10 percent of 

the population dies (Wygant 1938). Larval mortality increases to 25 

percent at -25oF (Wygant 1938).

From October 2003 to April 2004, the lowest winter temperature at the Fraser Experimental Forest headquarters 

at 9000 ft was -24oF on February 12, 2004, and all other 

minimum temperatures were higher than -20oF.2 This suggests that winter minimum monthly temperature(s) may 

not have caused extensive larval mortality. Further, the 

average minimum monthly temperatures from November 

2003 through March 2004 at the headquarters compound 

were generally warmer than the long-term minimum averages for four of the five months2

. Average minimum 

monthly temperatures (86 percent for November 2003, 

79 percent for December 2003, 61 percent for January 

2004, and 98 percent for March 2004) were warmer than 

the long-term averages2. Only in February 2004 was the 

average minimum monthly temperature colder than the 

long-term average minimum temperature2. During that 

month, the average minimum temperature was colder 

about 64 percent of the time. If winters are relatively 

milder, temperature presumably would have less influence on MPB mortality and more beetles would survive. 

In years of relatively mild winter weather when minimum temperatures rarely drop below -25o

F, the 9500 ft 

threshold may have to be modified for Colorado, i.e., the 

upper elevational limit for highly susceptible stands in 

the Amman and others (1977) rating method should be 

raised to ≥10,000 ft.

References_____________________

Amman, G.D.; McGregor, M.D.; Cahill, D.B.; Klein, W.H. 1977. 

Guidelines for reducing losses of lodgepole pine to the mountain 

pine beetle in unmanaged stands in the Rocky Mountains. Gen. 

Tech. Rep. INT-36. Ogden, UT: U.S. Department of Agriculture, 

2 L.Porth, statistician at the Rocky Mountain Research Station, US Forest 

Service, Fort Collins, CO, provided the temperature information as derived 

from the long-term temperature records taken at the Fraser Experimental 

Forest headquarters.

Forest Service, Intermountain Forest and Range Experiment 

Station. 19 p.

McCambridge, W.F. 1964. Emergence period of Black Hills beetles 

from ponderosa pine in the central Rocky Mountains. Res. 

Note RM-32. Fort Collins, CO: U.S. Department of Ariculture, 

Forest Service, Rocky Mountain Forest and Range Experiment 

Station. 4 p.

McCambridge, W.F. 1967. Nature of induced attacks by the Black 

Hills beetle, Dendroctonus ponderosae (Coleoptera: Scolytidae). 

Annals Entomological Society of America. 60: 920-928.

Negron, J.F.; Shepperd, W.D.; Mata, S.A.; Popp, J.B.; Asherin, 

L.A.; Schoettle, A.W.; Schmid, J.M.; Leatherman, D.A. 2001. 

Solar treatment for reducing survival of mountain pine beetle 

in infested ponderosa and lodgepole pine logs. Res. Pap. RMRSRP-30. Fort Collins, CO: U.S. Department of Ariculture, Forest 

Service, Rocky Mountain Research Station. 11 p.

Mielke, P.W. Jr.; Berry, K.J. 2001. Permutation methods—A distance 

function approach. Springer. 352 p. 

Rasmussen, L. A. 1974. Flight and attack behavior of mountain pine 

beetles in lodgepole pine of northern Utah and southern Idaho. 

Res. Note INT-180. Ogden, UT: U.S. Department of Agriculture, 

Forest Service, Intermountain Forest and Range Experiment 

Station. 7 p.

Rasmussen, L.A. 1980. Emergence and attack behavior of the 

mountain pine beetle in lodgepole pine. Res. Note INT-297. 

Ogden, UT: U.S. Department of Agriculture, Forest Service, 

Intermountain Forest and Range Experiment Station. 7 p.

Reid, R.W. 1962. Biology of the mountain pine beetle, Dendroctonus 

monticolae Hopkins, in the east Kootenay Region of British 

Columbia. I. Life cycle, brood development, and flight periods. 

Canadian Entomologist 94: 531-538.

Reid, R.W. 1963. Biology of the mountain pine beetle, Dendroctonus 

monticolae Hopkins, in the east Kootenay Region of British 

Columbia. III. Interaction between the beetle and its host, 

with emphasis on brood mortality and survival. Canadian 

Entomologist 95: 225-238.

Safranyik, L.; Jahern R. 1970. Emergence patterns of the mountain 

pine beetle from lodgepole pine. Canadian Department of 

Fisheries and Forests Bimonthly Res. Notes 26:11, 19

Schmid, J.M. 1972. Emergence, attack densities, and seasonal 

trends of mountain pine beetle (Dendroctonus ponderosae) 

in the Black Hills. Res. Note RM-211. Fort Collins, CO: U.S. 

Department of Ariculture, Forest Service, Rocky Mountain 

Research Station. 7 p.

Wygant, N.D. 1938. Critical low temperatures for the Black 

Hills beetle 1937-1938. Unpublished data on file at the Rocky 

Mountain Research Station, Fort Collins, Colorado. 27 p.

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