Influence of elevation on bark beetle (Coleoptera ... · droctonus brevicomis LeConte, and D....

COMMUNITY AND ECOSYSTEM ECOLOGY

Influence of Elevation on Bark Beetle (Coleoptera: Curculionidae,Scolytinae) Community Structure and Flight Periodicity in

Ponderosa Pine Forests of Arizona

KELLY K. WILLIAMS,1,2 JOEL D. MCMILLIN,3 TOM E. DEGOMEZ,1

KAREN M. CLANCY,4 AND ANDY MILLER1

Environ. Entomol. 37(1): 94Ð109 (2008)

ABSTRACT We examined abundance and ßight periodicity of Þve Ips and sixDendroctonus species(Coleoptera: Curculionidae, Scolytinae) among three different elevation bands in ponderosa pine(Pinus ponderosaDouglas ex. Lawson) forests of northcentral Arizona. Bark beetle populations weremonitored at 10 sites in each of three elevation bands (low: 1,600Ð1,736 m; middle: 2,058Ð2,230 m; high:2,505Ð2,651 m) for 3 yr (2004Ð2006) using pheromone-baited Lindgren funnel traps. Trap contentswere collected weekly from March to December. We also studied temperature differences among theelevation bands and what role this may play in beetle ßight behavior. Bark beetles, regardless ofspecies, showed no consistent elevational trend in abundance among the three bands. The higherabundances of Ips lecontei Swaine, I. calligraphus ponderosae Swaine,Dendroctonus frontalis Zimmer-man, andD. brevicomisLeConte at low and middle elevations offset the greater abundance of I. knausiSwaine, D. adjunctus Blandford, D. approximatus Dietz, and D. valens LeConte at high elevations. I.pini (Say) and I. latidens LeConte were found in similar numbers across the three bands. Flightperiodicity of several species varied among elevation bands. In general, the ßight period shortenedas elevation increased; ßight initiated later and terminated earlier in the year. The timing, number,and magnitude of peaks in ßight activity also varied among the elevation bands. These results suggestthat abundance and ßight seasonality of several bark beetles are related to elevation and the associatedtemperature differences. The implications of these results are discussed in relation to bark beetlemanagement and population dynamics.

KEY WORDS Dendroctonus, Ips, ßight seasonality, abundance, Pinus ponderosa

Bark beetles (Coleoptera: Curculionidae, Scolytinae)are a signiÞcant source of insect-caused pine mortalityin the western United States (Furniss and Carolin1977). Bark beetleÐcaused tree mortality is frequentlyrelated to certain tree and stand conditions (Fettig etal. 2007 and references cited therein). Identifyingthese patterns of mortality can facilitate the develop-ment of management strategies, such as silviculturaltreatments (Hedden 1981). Although hazard ratingsystems that relate forest susceptibility to stand char-acteristics have been developed for some bark beetlespecies (Steele et al. 1996, Schmitt and Powell 2005),tree mortality patterns related to physiographic char-acteristics have not received as much attention. Sitequality(Negronet al. 2000), latitude(Bentzet al. 2001,

Fettig et al. 2004a), and elevation (Hansen 1996, Sali-nas-Moreno et al. 2004, Fettig et al. 2005) have directand indirect effects on both hosts and herbivores andcan also be important in hazard rating systems. Tem-perature and precipitation, both environmental fac-tors affected by elevation (Sheppard et al. 2002), caninßuence tree vigor (Furniss and Carolin 1977, Allenand Breshears 1998, Ayres and Lombardero 2000),limit the geographic distribution of insects (Furnissand Carolin 1977, Ungerer et al. 1999, Ayres and Lom-bardero 2000, Lombardero et al. 2000, Bale et al. 2002,Williams and Liebhold 2002), and regulate bark beetlephenology and voltinism (Furniss and Carolin 1977,Ungerer et al. 1999, Ayres and Lombardero 2000, Han-sen et al. 2001, Bale et al. 2002). Bark beetle speciesinfesting hosts with wide physiographic ranges will beexposed to a broad array of temperature effects.

Differential adaptation to temperature regimensamong species may result in unique bark beetle as-semblages along elevational gradients. Environmentalfactors associated with elevation in the Sierra NevadaMountains of California inßuenced both the spatialand temporal distribution of four major bark beetlespecies [Ips pini (Say), I. paraconfusus Lanier, Den-

1 University of Arizona, School of Natural Resources, NAU Box15018, Flagstaff, AZ 86011.

2 Corresponding author, e-mail: [email protected] USDA Forest Service, Southwestern Region, Forestry and For-

est Health, Arizona Zone, 2500 S. Pine Knoll Dr., Flagstaff, AZ86001-6381.

4 USDA Forest Service Research and Development, RockyMountain Research Station, 2500 S. Pine Knoll Dr., Flagstaff, AZ86001-6381.

0046-225X/08/0094Ð0109$04.00/0 � 2008 Entomological Society of America

droctonus brevicomis LeConte, and D. ponderosaeHopkins] (Fettig et al. 2005). Two species (I. para-confusus and D. brevicomis) were inversely related toelevation, whereas the other two species (I. pini andD. ponderosae) did not display a speciÞc pattern withrespect to elevation. In addition, temperature effectsassociated with elevational gradients have been re-ported to inßuence ßight initiation and cessation, de-velopment time, or number of generations for severalbark beetles species, including Dryocoetes confususSwaine in Utah (Hansen 1996) andD. rufipennisKirbyin Utah, Colorado, and Alaska (Hansen et al. 2001).Outside of these few studies, there is a paucity ofinformation on spatial/temporal variation of bark bee-tle communities across elevational gradients of theirhosts.

The bark beetle community in ArizonaÕs ponderosapine (Pinus ponderosa Douglas ex. Lawson) forests iscomplex, comprised of several primary (i.e., capable ofattacking, colonizing and killing apparently healthytrees) and secondary (i.e., infesting weakened, dead,or dying trees) bark beetle species. Based on a reviewof bark beetle taxonomical records, 29 species of barkbeetles, including six Dendroctonus spp. and 12 Ipsspp., attack branches, trunks, and roots of ponderosapine in the southwestern United States (Furniss andCarolin 1977, Wood 1982). Bark beetles recentlycaused unprecedented levels of ponderosa pine mor-tality throughout Arizona (USDA 2001Ð2004). Pri-mary tree-killing species included I. pini, I. leconteiSwaine, D. brevicomis, and D. frontalis Zimmerman;however, their relative importance varied by site andelevation (J.D.M., unpublished data). The communitystructure and ßight periodicity of bark beetles innorthcentralArizonaponderosapine forestshaveonlybeen examined at one elevation (2,080 m) near Flag-staff, AZ (Sanchez-Martinez and Wagner 2002, Gay-lord et al. 2006). To date, knowledge has been lackingon how this bark beetle community and the ßightperiodicity of individual species vary across a broaderelevational gradient.

The primary objective of this study was to describespecies composition, abundance, and ßight periodicityof Dendroctonus and Ips genera occurring in pon-derosa pine forests across an elevational gradient innorthcentral Arizona. Species composition, abun-dance, and ßight periodicity were determined usingLindgren funnel traps baited with aggregation pher-omones. The second objective was to study the roletemperature plays in regulating ßight behavior ofthese bark beetle species. Knowledge gained from thisproject has implications for development of hazardrating systems, timing of silvicultural, semiochemical,and preventative spray treatments, and prediction ofbark beetle population dynamics.

Methods and Materials

Site Description. Study sites were located in standsof ponderosa pine on the Coconino, Kaibab, andTonto National Forests in north central Arizona (Fig.1). All sites were located in the interior ponderosa

pine cover type of the Society of American Foresters(Eyre 1980). Xerophytic forests at low elevations(1,600Ð1,736 m) were bordered by pinyon/juniperwoodlands and included trees and shrubs such as pin-yon pine (P. edulis Engelm.), alligator juniper (Juni-perus deppeana Steud.), Utah juniper (J. osteosperma(Torr.) Little), Arizona white oak (Quercus arizonicaSarg.), manzanita (Arcostaphylos pungensKunth), andyuccas (Yucca spp.) (Moir et al. 1997, USDA 2002a).Middle elevation xerophytic forests (2,058Ð2,230 m)were dominated by ponderosa pine. Associated un-derstory vegetation ranged from bunchgrasses to one-seed juniper [J. monosperma (Engelm.) Starg.] andGambel oak (Q. gambelii Nutt.) (Moir et al. 1997,USDA 2002b). Ponderosa pine stands were intermin-gled with mixed conifer stands in the high elevationband (2,505Ð2,651 m), and sites were located in bothxerophytic and mesophytic forest zones (Moir et al.1997). Additional tree species found at high elevationsites included Douglas Þr [Pseudotsugamenziesii(Mir-bel) Franco], limber pine (P. flexilis James), white Þr[Abies concolor (Gord. and Glend.) Lindl. ex Hildebr.variety concolor], and quaking aspen (Populus tremu-loidesMichx.) (Moir et al. 1997, USDA 2002b, 2002c).

According to the General Ecosystem Survey (Car-leton et al. 1991), these sites are mostly located in theHigh Sun Mild (low elevation) and High Sun Cold(highelevation)climatezones,wheremeanannual airtemperatures range from 4 to 9�C, and mean annualprecipitation ranges from 520 to 700 mm (Moir et al.1997). Precipitation primarily falls in two differenttimes of the year. Summer precipitation occurs fromJuly to September, whereas winter precipitation fallsfrom December through March (Hendricks 1985).Study Design. Ten sites were established in each of

three elevation bands that covered most of the eleva-tional range of ponderosa pine in Arizona: low (1,600Ð1,736 m), middle (2,058Ð2,230 m), and high (2,505Ð2,651 m). Sites within an elevation band wereseparated by a minimum of 2 km. Trap sites werewithin 100 m of the edge of ponderosa pine stands andwithin 50Ð200 m of forest roads to facilitate collec-tions. Efforts were made to maintain the same trappinglocations each year; however, forest management ac-tivities and forest road closures required the removalof one low elevation site and one high elevation siteand the relocation of one low elevation site and onemiddle elevation site. Relocation sites were within 9km of the original sites.

Each trap site contained three 12-unit Lindgrenfunnel traps (Pherotech International, Delta, BritishColumbia, Canada) (Lindgren 1983) arranged in an�15-m equilateral triangle. Traps were suspendedfrom 3-m aluminum conduit poles with the bottom oftraps �1 m from the ground. Traps were baited withlures that targeted three species of concern in north-central ArizonaÕs ponderosa pine forests: I. pini, I.lecontei, and D. brevicomis (Table 1). Although theselure combinations targeted certain species, they werealso expected to capture other Ips and Dendroctonusspecies based on a previous study in northern Arizona(Gaylord et al. 2006). Lures were replaced every 7 wk

February 2008 WILLIAMS ET AL.: ELEVATION EFFECTS ON PINE BARK BEETLE COMMUNITIES 95

to ensure adequate pheromone elution rates. Trapswere also rotated on a regular basis to minimize lo-cation impacts. A 2.5 by 2.5-cm square of SpectracideBug Stop pest strip (18.6% Dichlorvos; United Indus-tries, St. Louis, MO) was placed in each collection cupto kill trapped insects and minimize predation.

The length of trapping season varied across eleva-tion and year (Table 2) and was initially based on theresults of a recent study near Flagstaff, AZ (Gaylordet al. 2006). Initiation and cessation of trapping at highelevation sites in all years depended on site accessi-bility caused by spring and fall weather. Based on 2004data, efforts were made in 2005 and 2006 to extend thelength of the trapping seasons for all elevations so thattrap catch data would start and end with zero trap

catches, reßecting a true initiation and cessation ofßight activity for all species.

Contents of traps were collected approximatelyonce per week. All beetles of the genera Ips andDendroctonus were identiÞed and tallied. Bark beetlespecies were identiÞed using WoodÕs (1982) taxo-nomic monograph for bark beetles. Species identiÞ-cations were conÞrmed by using existing collections atNorthern Arizona University (Flagstaff, AZ) and theRocky Mountain Research Station (Flagstaff, AZ), byindependently comparing samples with collectionshoused at Texas Agricultural and Mechanical Univer-sity (conducted by Anthony Cognato, Department ofEntomology, Texas Agricultural and Mechanical Uni-versity, College Station, TX), and by genetic sequenc-ing (conducted by Chris Allender, the Center forMicrobial Genetics and Genomics, Northern ArizonaUniversity, Flagstaff, AZ). Voucher specimens are

Fig. 1. Map showing the location of low (1,600Ð1,736 m), middle (2,058Ð2,230 m), and high (2,505Ð2,651 m) elevationtrap sites in ponderosa pine forests of northcentral Arizona used in all 3 yr of study, 2004Ð2006.

Table 1. Description of semiochemical lures (Pherotech In-ternational, Delta, British Columbia, Canada) used in Lindgrenfunnel traps located in three elevation bands in the Coconino,Kaibab, and Tonto National Forests, Arizona, 2004–2006

Bark beetlespecies

Semiochemical lureChemicalpurity (%)

Release rate(mg/24 h)

I. pini Ipsdienol �03/�97 �95 0.2 @ 25�CLanierone �97 0.009 @ 25�C

I. lecontei Ipsdienol �50/�50 �95 0.2 @ 25�CIspsenol �50/�50 �96 0.4 @ 25�CCis-verbenol �17/�83 �90 0.6 @ 20�C

D. brevicomis Frontalin �99 2.6 @ 23�CExo-brevicomin �99 1.7 @ 23�CMyrcene (�2) �90 6.5 @ 23�C

Table 2. Dates of sampling bark beetle flight in ponderosa pineforests on the Coconino, Kaibab, and Tonto National Forests,Arizona, 2004–2006

Year

Elevation band

Low(1,600Ð1,736 m)

Middle(2,058Ð2,230 m)

High(2,505Ð2,651 m)

2004 12 April to 16 Nov. 13 April to 15 Nov. 28 April to 15 Nov.2005 8 Mar. to 6 Dec. 23 Mar. to Dec. 8. 25 April to 28 Nov.2006 7 Mar. to 12 Dec. 9 Mar. to 7 Dec. 27 Mar. to 6 Dec.

96 ENVIRONMENTAL ENTOMOLOGY Vol. 37, no. 1

maintained at the Rocky Mountain Research Station,United States Forest Service, Flagstaff, AZ.

HOBO data loggers (Onset Computer, Bourne,MA) were installed at diameter breast height (1.37 m)on the north side of a tree nearest to the center of thetrap site at six sites in each elevation band. In 2004, dataloggers collected temperature data for the duration ofthe trapping season (Table 2). In 2005, data loggerswere reinstalled as traps were deployed in each ele-vation band, so temperature data collection startedmuch later at high elevation sites than at low elevationsites (Table 2). Data loggers remained in the Þeldthroughout the winter of 2005/2006 and continuedcollecting temperature data through the 2006 trappingseason.Statistical Analysis. For each site and collection pe-

riod, beetle count was summed across all three traps.Because each lure combination targeted a differentspecies of bark beetle, a wide variety ofDendroctonusand Ips species were attracted to the site and collectedin all three traps. Therefore, the beetle count summedacross all three traps represents the total beetle cap-ture for a given site. Although most trap collectionperiods were 1 wk, collection periods ranged from 4 to17 d. To standardize data, the total trap catch per sitefor a collection period was divided by the number ofdays in that collection period and multiplied by 7 togive a value representing the total trap catch for aweek.

The average weekly beetle capture for the trappingseason was calculated for each site using data fromcollection weeks when at least one trap was deployedin each elevation band. Only sites that were installedall 3 yr were included in the analysis. The mean beetlecapture for each elevation band was compared forpooled years using a multiple response permutationprocedure (MRPP) (Mielke and Berry 2001) for one-factor designs (macros developed by Rudy King,USDA Forest Service, Rocky Mountain Research Sta-tion Statistics Unit). MRPP, a nonparametric tech-nique, is similar to analysis of variance (ANOVA) butdoes not require normal distribution and equal vari-ance of the data (Mielke and Berry 2001). All testswere run with a signiÞcance level of � � 0.05. Meanweekly trapcatchper site(�SEM)wasplottedagainsttime for pooled years to supplement the MRPP anal-ysis. These graphs provided insight into peak barkbeetle captures, along with the initiation and cessationof bark beetle ßight activity. By pooling years, overallelevational trends of bark beetle abundance and ßightperiodicity could be observed. Additionally, temporalgraphs of individual years were constructed to exposeannual ßuctuations in the seasonal patterns of trapcatches within an elevation band.

Hourly temperatures were converted to maximum,minimum, and average weekly temperatures. A one-way ANOVA was performed to test for differences inthe mean temperature (maximum, minimum, and av-erage weekly temperature) across the trapping seasonamong the low, middle, and high elevation bands.Only sites with complete data and only weeks whendata were collected in all elevation bands were used.

Because signiÞcant data loss occurred in 2004, onlydata from 2005 and 2006 were used in the analysis.Temperature data were collected from all elevationbands from the weeks of 26 April to 29 November 2005and from the weeks of 7 March to 4 December 2006.

Results

Beetle Abundance. A total of 90,558 bark beetles,comprising Þve Ips species and six Dendroctonus spe-cies, were collected over three trapping seasons. Ipsspecies included I. pini, I. lecontei, I. calligraphus pon-derosae Swaine, I. latidens LeConte, and I. knausiSwaine.Dendroctonus species includedD. frontalis, D.brevicomis, D. adjunctus Blandford, D. approximatusDietz, D. valens LeConte, and D. ponderosae. All spe-cies, other thanD. ponderosae,were found in all threeelevationbands.D.ponderosaewasonlycapturedat sixhigh elevation sites and one middle elevation site.Total Scolytinae abundance was similar across theelevation bands of this study (P� 0.682). Separated bygenera, Dendroctonus abundance was similar amongthe three bands (P � 0.926), whereas Ips abundancewas different among the elevation bands (P� 0.050).Ips species as a whole were more abundant at low andmiddle elevations compared with high elevations.Ips lecontei and I. calligraphus ponderosae abun-

dance differed among the elevation bands (Table 3).Both species were most common at low elevation sites,and abundance decreased with each increase in ele-vation band.D. frontaliswas most abundant at low andmiddle elevation sites, whereasD.brevicomiswas mostcommon in the middle elevation band (Table 3). I.knausi, D. approximatus, and D. valens were mostabundant at high elevation sites (Table 3). Dendroc-tonus adjunctus was most common at high elevationsites; abundance decreased with each decrease in el-evation band (Table 3). I. pini and I. latidens abun-dance was similar across elevations (Table 3).D. pon-derosae (data not shown) abundance was low amongall the elevation bands and therefore was not statis-tically analyzed; however, most beetles (97.9% of 48)were caught at high elevation sites.

Table 3. P values for MRPP testing for differences in beetlespecies abundance among low (1,600–1,736 m), middle (2,058–2,230 m), and high (2,505–2,651 m) elevation bands in north-central Arizona

Species

P value

Allbandsa

L versusM

L versusH

M versusH

I. pini 0.240 Ñ Ñ ÑI. lecontei 0.001 0.007 0.001 0.031I. calligraphus 0.001 0.027 0.001 0.012I. latidens 0.569 Ñ Ñ ÑI. knausi 0.001 0.162 0.001 0.001D. frontalis 0.001 0.058 0.001 0.009D. brevicomis 0.013 0.017 0.217 0.024D. adjunctus 0.001 0.001 0.001 0.003D. approximatus 0.002 0.112 0.005 0.007D. valens 0.002 0.207 0.001 0.019

aHo, low, middle, and high elevation means are similar; L, lowelevation band; M, middle elevation band; H, high elevation band.


Flight Periodicity. Ips pini ßight activity in the lowelevation band occurred from at least early Marchthrough November (Fig. 2). In general, ßight wasinitiated 1Ð4 wk later and was terminated 1Ð2 wkearlier with each increase in elevation band. Therewere distinct peaks in beetle captures in all elevation

bands, but the number, timing, and magnitude of thosepeaks varied across elevation and years (Fig. 3; onlydata for low elevation sites are plotted). Because ofthis annual variation, temporal patterns for each yearwere analyzed individually. I. pini trap catches werehighest in 2005 in all elevation bands. At low elevation

Fig. 2. Seasonal beetle captures of I. pini at low (1,600Ð1,736 m), middle (2,058Ð2,230 m), and high (2,505Ð2,651 m)elevation bands in ponderosa pine forests of northcentral Arizona, 2004Ð2006.

Fig. 3. Annual graphs of seasonal trap catches of I. pini in the low elevation band (1,600Ð1,736 m) in ponderosa pine forestsof northcentral Arizona, 2004Ð2006.


sites in 2005, there were four distinct peaks in I. pinicaptures observed in March, July, August, and Octo-ber. Peaks in trap captures for 2004 and 2006 weresmaller in magnitude and less synchronous acrosssites. In addition, a fall peak in trap catches was notobserved. At middle elevation sites in 2005, springßight activity was followed by large peaks in July andOctober (data not shown). As in the low elevationband, peaks in ßight activity were much smaller andless synchronous across sites in 2004 and 2006. At highelevation sites in 2005, July and September peaks wereobserved (data not shown). In 2006, traps were de-ployed a month earlier, and an April peak in trapcatches was observed before dropping to much lowernumbers the rest of the season. No distinct peaks wereobserved in 2004.Ips lecontei ßight activity was recorded as early as

the Þrst week of March and as late as the Þrst week ofDecember (Fig. 4). With each increase in elevationband, ßight activity began at least 1Ð2 wk later andterminated at least 1Ð2 wk earlier. Beetle captureswere low in the middle and high elevation bands, soseasonal abundance patterns were only analyzed inthe low elevation band. Similar to I. pini, seasonalabundance was analyzed by year, because there wasdistinctive annual variation in the temporal patterns oftrap catches (Fig. 5; only data for low elevation sitesare plotted). However, there was also a high degree ofvariation among sites each year. For example, peaksobserved in the summers of 2004 and 2005 in the lowelevation band were driven by high trap catches atonly a few sites, and these sites accounted for approx-imately one half of the total I. lecontei captured at lowelevations.

Ipscalligraphusponderosaeßightactivitywasobservedas early as the Þrst week of March and as late as the endof November (Fig. 6). Flight initiation was delayed 1Ð3wk with each increase in elevation band and endedalmost 4 wk earlier in the high elevation band than in thelow and middle elevation bands. There was annual vari-ation in the temporal pattern of trap catches, so yearswere analyzed individually (data not shown). In 2004and 2005, there were three peaks in trap catches in thelow elevation band observed in the spring, summer, andfall. In 2006, I. calligraphus ponderosae abundance de-clined sharply, and no peaks were observed. In 2004 and2006, there were two peaks in captures at middle eleva-tion sites, occurring in May and October (data notshown). In 2005, the highest trap catch occurred in July(data not shown). There was minimal ßight activity athigh elevation sites (Fig. 6).Ips latidens captures were low throughout the trap-

ping study, collecting 200 beetles each year in eachelevation band (Fig. 7). Flight activity began by mid-April in all elevation bands and peaked by early May.A midsummer increase in ßight activity was observedin the low and middle elevation bands. I. latidensßightactivity ended by late September at all elevations.Ips knausi trap catches were low, totaling 100

beetles each year in each elevation band (data notshown). I. knausi were caught as early as mid-Marchand as late as mid-November; however, beetles wereonly captured in the spring and fall. At high elevations,93.7% of the 158 I. knausi captured were caught fromSeptember to November. The other 6.7% were cap-tured in April and May.Dendroctonus frontalis ßight activity occurred from

early March to late November (Fig. 8). With each

Fig. 4. Seasonal beetle captures of I. lecontei at low (1,600Ð1,736 m), middle (2,058Ð2,230 m), and high (2,505Ð2,651 m)elevation bands in ponderosa pine forests of northcentral Arizona, 2004Ð2006.


increase in elevation band, spring ßight activity wasdelayed by �1 mo, whereas ßight activity usually ter-minated within 1 wk of each other. At low elevations,there was low to moderate ßight activity through thespring and summer, followed by a large increase inbeetlecaptures fromSeptember toNovember.Atmid-

dle elevation sites, beetle numbers remained fairly lowduring the spring, but ßight activity increased fromJuly to October. At high elevations, ßight activity waslow throughout the year.Dendroctonus brevicomis ßight activity occurred

from early March to late November (Fig. 9). In gen-

Fig. 5. Annual graphs of seasonal trap catches of I. lecontei in the low elevation band (1,600Ð1,736 m) in ponderosa pineforests of northcentral Arizona, 2004Ð2006.

Fig. 6. Seasonal beetle captures of I. calligraphus ponderosae at low (1,600Ð1,736 m), middle (2,058Ð2,230 m), and high(2,505Ð2,651 m) elevation bands in ponderosa pine forests of northcentral Arizona, 2004Ð2006.


eral, ßight initiation was delayed by 1 mo with eachincrease in elevation band, whereas ßight terminationoccurred within 1 wk of each other. In the low andmiddle elevation bands, D. brevicomis ßight activitywas steady throughout the trapping season, with nodistinct peaks in beetle captures. In the high elevation

band, increased beetle catches occurred in May andJune before falling to lower numbers the rest of theseason.

Two distinct ßight periods were recorded for D.adjunctus, one in the spring and the other in the fall(Fig. 10). The smaller spring ßight occurred from late

Fig. 7. Seasonal beetle captures of I. latidens at low (1,600Ð1,736 m), middle (2,058Ð2,230 m), and high (2,505Ð2,651 m)elevation bands in ponderosa pine forests of northcentral Arizona, 2004Ð2006.

Fig. 8. Seasonal beetle captures ofD. frontalis at low (1,600Ð1,736 m), middle (2,058Ð2,230 m), and high (2,505Ð2,651 m)elevation bands in ponderosa pine forests of northcentral Arizona, 2004Ð2006.


March to early July and the larger fall ßight occurredfrom early September to late November. With eachincrease in elevation band, the proportion of beetlescaptured in the spring also increased. At middle ele-vations, the spring capture accounted for only 13.8% ofthe 3,371 beetles caught, whereas at high elevations,

the spring ßight accounted for 27.6% of the 8,480beetles captured.Dendroctonus approximatus ßight activity occurred

from early March to mid-November (Fig. 11). Witheach increase in elevation band, beetle ßight was ini-tiated 1Ð2 wk later. Flight activity at high elevation

Fig. 9. Seasonal beetle captures of D. brevicomis at low (1,600Ð1,736 m), middle (2,058Ð2,230 m), and high (2,505Ð2,651m) elevation bands in ponderosa pine forests of northcentral Arizona, 2004Ð2006.

Fig. 10. Seasonal beetle captures of D. adjunctus at low (1,600Ð1,736 m), middle (2,058Ð2,230 m), and high (2,505Ð2,651m) elevation bands in ponderosa pine forests of northcentral Arizona, 2004Ð2006.


sites terminated�3wkearlier than the lowandmiddleelevation sites. In the low and middle elevation bands,beetle captures peaked in the spring (April/May)before tapering off to lower numbers the rest of theseason. At high elevations, there was a May peak in

beetle captures, followed by another increase in trapcatches in June and July.Dendroctonus valens ßight activity occurred from

early April to late October (Fig. 12). Flight initiationand cessation occurred within 1Ð2 wk of each other

Fig. 11. Seasonal beetle captures ofD.approximatusat low (1,600Ð1,736 m), middle (2,058Ð2,230 m), and high (2,505Ð2,651m) elevation bands in ponderosa pine forests of northcentral Arizona, 2004Ð2006.

Fig. 12. Seasonal beetle captures of D. valens at low (1,600Ð1,736 m), middle (2,058Ð2,230 m), and high (2,505Ð2,651 m)elevation bands in ponderosa pine forests of northcentral Arizona, 2004Ð2006.


across elevation. At all elevations, a spring peak inbeetle captures was followed by lower beetle ßightactivity in the summer. Few beetles were captured inthe fall.

Although only 48 D. ponderosae were captured inthis study, the majority (77.1%) of trap catches oc-curred from early August to early September (data notshown).Temperature. Average and maximum weekly tem-

peratures varied among elevation bands (P 0.001 for2005 and 2006; Fig. 13; only data for 2006 plotted).However, minimum weekly temperatures did not sig-niÞcantly differ across elevation (P� 0.451, 2005; P�0.132, 2006; Fig. 13). In 2005 and 2006, the averagemaximum weekly temperature in the low band was 2.8and 3.6�C warmer than the middle elevation band,which was 4.5 and 4.4�C warmer than the high eleva-tion band.

Discussion

Beetle Abundance and Seasonality Across Eleva-tion.According to our data, the elevation range withinwhich ponderosa pine grows in northcentral Arizonais suitable habitat for most Ips and Dendroctonus spe-cies. Ten of the 11 species collected were foundthroughout the entire elevation range of the study(1,600Ð2,651 m). Total Scolytinae abundance, regard-less of species, was similar among elevation bands.Dendroctonus abundance showed no strong eleva-

tional trends, whereas Ips abundance was greatest inthe low and middle elevation bands. I. lecontei, D.frontalis, and D. brevicomis, all considered primarytree killing species in Arizona, should be more of aconcern at elevations between 1,600 and 2,230 m,whereas D. adjunctus should be a concern in pon-derosa pine above 2,505 m. I. pini should be consideredan important threat at all elevations.

Elevational trends present in the distribution ofcertain bark beetle species suggest that elevationshould be a factor included in ponderosa pine standhazard ratings speciÞc to the southwest. However,elevation trends for certain species may vary fromregion to region. For example, in the Sierra Nevada,D.brevicomis abundance was inversely related to eleva-tion (Fettig et al. 2005), whereas, in Arizona,D. brevi-comis was most abundant in the middle elevationband. Consequently, inclusion of an elevation factorand how it interacts with stand characteristics in standhazard ratings systems should be speciÞc to individualregions.

Our observations on ßight periodicity agree withprevious reports for many species in the southwest.However, several aspects of ßight seasonality, includ-ing length of ßight season and timing of peak ßightactivity, varied across elevation and occasionallyamong years. Although bark beetle ßight activity oc-curred from March through December at lower ele-vations, the ßight period generally shortened as ele-vation increased. The shortened ßight period was

Fig. 13. Weekly maximum, average, and minimum temperatures for low (1,600Ð1,736 m), middle (2,058Ð2,230 m), andhigh (2,505Ð2,651 m) elevation bands in ponderosa pine forests of northcentral Arizona, 07 March 2006 to 4 December 2006.


primarily a result of delayed ßight initiation in thespring.Flight initiationoccurredat least 2Ð4wkearlierat low and middle elevations compared with highelevation sites for several species. Knowledge of ßightactivity for several species and how it changes acrosselevation should improve timing of forest manage-ment activities in Arizona.Ips pini abundance was similar in all elevation bands

(Fig. 2). This Þnding agrees with a recent SierraNevada, CA, study that found no signiÞcant relation-ship between trap catch of I. pini and elevation (Fettiget al. 2005). I. pini ßight activity began in March at lowand middle elevation sites, whereas spring ßight ini-tiated �1 mo later in the high elevation band. Atmiddle and high elevations, there were three peaks inbeetle captures occurring in April/May, June/July,and September/October, suggesting two generationsper year, which agrees with previous reports on I. pinißight activity (Livingston 1979, Parker 1991, Kegley etal. 1997, Gaylord et al. 2006). In the low elevationband, there appeared to be four peaks in ßight activity(one in the spring, two in the summer, and one in thefall) in 2005 (Fig. 3), suggesting three generations peryear. Warmer temperatures (in the low elevationband) favor a longer period of ßight activity and fasterdevelopment time for each generation (Livingston1979). The temporal pattern in trap catches in 2004and 2006 at low elevation sites was different than in2005, when I. pini abundance was higher. The 2004 and2006 patterns were weaker because the timing of peakbeetle captures was not as synchronous across sites.This asynchrony may be explained by lower beetleabundance these 2 yr. It has been suggested that whenpopulation density is low, there tends to be asyn-chrony between peaks in emergence and dispersalßights (Gara et al. 1999). Conversely, as populationsincrease to epidemic numbers, emergence and dis-persal become more synchronized.Ips leconteiwas most abundant in the low elevation

band (Fig. 4). This Þnding corresponds with obser-vations that ponderosa pine mortality caused by I.leconteioccurs primarily at the lower elevational rangeof ponderosa pine in Arizona (Parker 1991). I. leconteißight activity at low and middle elevations began inMarch, which corresponds with recent observationson ßight initiation near Flagstaff, AZ (elevation, 2,080m) (Gaylord et al. 2006). I. lecontei has been reportedto emerge in April and May in Arizona (Chansler 1964,Ostmark 1966, Massey and Parker 1981), whichmatches our results for the high elevation band. Ourobserved dates of ßight termination (NovemberÐDe-cember) are later than observations by Gaylord et al.(2006) but similar to those of Ostmark (1966) in astudy on the Prescott National Forest, AZ (elevation,1,800 m). I. lecontei is reported to have three gener-ations a year (Chansler 1964, Ostmark 1966, Furnissand Carolin 1977, Massey and Parker 1981). Becauseparent adults and their progeny are ßying and attack-ing trees at the same time, determining deÞnite ßightperiods for each generation can be difÞcult (Ostmark1966). Our study did not provide strong insight intothe ßight periodicity of I. lecontei. Peaks observed in

our data were not necessarily reßective of broodemergence across the elevation band, because theywere driven by high trap catches at one or two sitesoccurring at different times of the season (Fig. 5). Inaddition, the majority of beetle catches wereaggregated among a few sites.

To our knowledge, there is no published infor-mation on the biology and ßight seasonality of I.calligraphus ponderosae, the western subspecies of I.calligraphus (Germar) (Furniss and Carolin 1977).I. calligraphus ponderosae was most abundant at lowelevation sites (Fig. 6). Flight initiation at low eleva-tions occurred at least 1.5 mo earlier (March) thanßight initiation at middle and high elevations. At lowand middle elevation sites, ßight activity terminated inNovember but ended �1 mo earlier at high elevationsites. At low elevations there were spring, summer,and fall peaks in beetle captures. There appeared to bethe same pattern at middle elevations, but there wasmuch lower ßight activity in the middle elevationband, and peaks in captures were not as synchronousacross the sites.Ips latidens was equally abundant across elevation

(Fig. 7). I. latidens ßight activity occurred from Aprilto September in all elevation bands, which matchesthe ßight season observations by Gaylord et al. (2006).There was a distinct peak in beetle ßight activity dur-ing the spring, which is also consistent with previousreports on ßight activity of this species (Miller andBorden 1985, Gaylord et al. 2006). In addition, therewas a smaller increase in beetle captures that occurredin midsummer, which was most likely comprised ofreemerged adults (Miller and Borden 1985).Ips knausi was most abundant in the high elevation

band and was collected in the spring and fall, primarilyduring October and November. These Þndings agreewith a previous report on I. knausi ßight seasonality inthe Kaibab National Forest, AZ, north of the GrandCanyon, which also observed an association betweenI. knausi and D. ponderosae (Blackman 1931). Al-though the majority of I. knausi and D. ponderosaewere captured in the high elevation band of this study,D. ponderosae trap catches were too low to makeobservations on an association between the two spe-cies. However, seasonal beetle captures of I. knausicoincided with the spring and fall ßights ofD. adjunc-tus (Fig. 10). Additionally, the greatest number of I.knausi and D. adjunctus were captured at the samehigh elevation site. This may suggest that this Ipsspecies has a close association with D. adjunctus inareas whereD. adjunctus is prevalent andD. pondero-sae is not.Dendroctonus frontalis was most abundant in the

low and middle elevation bands (1,600Ð2,230 m; Fig.8), which overlaps with the preferred elevation range(1,100Ð2,000 m) found in Mexico (Salinas-Moreno etal. 2004). Flight initiation ofD. frontaliswas related toelevation, as spring ßight activity was delayed �1 mowith each increase in elevation band. Middle elevationßight activity occurred from April to November, con-sistent with recent Þndings on D. frontalis near Flag-staff, AZ (Gaylord et al. 2006). Previous research has


suggested that D. frontalis has three generations peryear near Flagstaff, AZ (Gaylord 2004). The numberof generations was difÞcult to interpret from the sea-sonal pattern of trap catches for any elevation band inour study. Although there was a large increase inbeetle captures that extended multiple months overthe summer and fall, there were no distinct peaks(suggesting brood emergence) in ßight activity thatwould suggest multiple generations within a trappingseason. This is most likely a reßection of overlappinggenerations (Wood 1982).

A previous report suggested that D. brevicomis wasmost commonly found in forests with a middle eleva-tion level between 600 and 1,800 m (DeMars andRoettgering 1982). In this study, D. brevicomis wasmost commonly found at an elevation range of 2,058Ð2,230 m and showed no clear elevational trend. Ourresults contrast with Þndings in the Sierra Nevada, CA,study that reportedan inverse relationshipbetweenD.brevicomis and elevation (Fettig et al. 2005).D. brevi-comis ßight initiation was delayed �1 mo with eachincrease in elevation band (Fig. 9). At low elevationsites, ßight activity occurred from March to Novem-ber. These results agree with previous research de-scribing D. brevicomis as having three to four gener-ations at lower elevations, with attacks occurring fromMarch to November (Massey 1961, DeMars and Roet-tgering 1982, Wood 1982). Flight activity at middleelevations occurred from April to November, whichcorresponds with previous Þndings by Gaylord et al.(2006) in this elevation band. At higher elevations,D.brevicomis is described as having two generations withattacks occurring in early June and late August (De-Mars and Roettgering 1982). Although D. brevicomiswasmoreactive in JuneandJulyathighelevation sites,the rest of the summer and fall had greatly reducedbeetle captures. There were no distinct peaks in D.brevicomis captures, suggestive of overlapping broodsor reemerging adults (Miller and Keen 1960, Massey1961, Stark and Dahlsten 1970, Wood 1982).

Timing of ßight activity was similar for D. frontalisand D. brevicomis (Figs. 8 and 9), with dates of ßightinitiation and cessation in each elevation band almostidentical for both species. Gaylord et al. (2006) re-ported similar seasonal patterns in D. brevicomis andD. frontalis captures at a study site near Flagstaff, AZ.This was not evident in the temporal graphs of eachspecies by elevation band. Synchrony between D.brevicomis and D. frontalis ßight activity seems to bemore of a site-speciÞc, rather than region-wide, oc-currence.

High elevation sites comprised the majority (70.1%of 12,090) of D. adjunctus trap catches, followed bymiddle (27.9%) and low elevation sites (2.0%). Thiscorresponds with a study in Mexico that establishedD.adjunctus, although found at elevations ranging from1,600 to 3,929 m, was more abundant at a higher ele-vation interval of 3,100Ð3,500 m (Salinas-Moreno et al.2004). The timing of D. adjunctus peak ßight activitywas relatively consistent across elevation (Fig. 10).There were two distinct ßight periods, one in each thespring and the fall, with little to no activity in between.

These Þndings are in agreement with earlier reportson D. adjunctus ßight activity (Blackman 1931, Chan-sler 1967, Massey et al. 1977, Wood 1982, Gaylord2004), suggesting 1Ð1.5 generations per year. Thespring ßight, which is mostly comprised of reemergedoverwintering adults (Chansler 1967), occurred inApril and May. The fall ßight occurred primarily inOctober. The proportion of reemerging adults ßyingin the spring increased as elevation increased.Dendroctonus approximatus was most abundant in

the high elevation band (2,505Ð2,651 m; Fig. 11),which is higher than the favored elevation interval(2,100Ð2,500 m) in Mexico (Salinas-Moreno et al.2004). In its northern range, ßight activity of thisunivoltine beetle starts in early June and ends in Oc-tober(Furniss andCarolin1977,Wood1982),whereasßight activity occurs year round in Mexico (Wood1982). Our results Þt somewhere between the two,because the ßight period at low elevation occurredfrom mid-March to mid-November. With each in-crease in elevation band, ßight activity began �2 wklater. Aside from a spring increase in beetle captures,there was no consistent pattern in trap catches acrosselevations or years. This lack of peak ßight activity wasmost likely caused by an extended emergence periodlasting through the spring and summer (Blackman1931, Wood 1982). In the high elevation band, thereappeared to be a second increase in beetle captures inJune and July, which is consistent with previousknowledge of peakD.approximatusßight activity in itsnorthern range (Wood 1982) and peak attack activityin Kaibab National Forest (Blackman 1931).Dendroctonus valenswas most abundant in the high

elevation band (2,505Ð2,651 m; Fig. 12), which ishigher than the favored elevation interval (2,100Ð2,500 m) for this species in Mexico (Salinas-Moreno etal. 2004). The length of ßight season forD. valens doesnot seem to be strongly related to elevation, becausethe ßight period occurred from April to October at allelevation bands. This period of ßight activity is similarto the reported ßight period in its northern range(Wood 1982). D. valens has one generation in 2 yr inthecoldestpartsof its range,butmayhave twoto threegenerations per year in warmer climates (Smith 1971).Our observations on ßight activity are similar to pre-vious Þndings on ßight periodicity ofD. valens (Black-man 1931, Smith 1971, Fettig et al. 2004b, 2006, Gay-lord et al. 2006). Flight activity peaked in May at allelevation bands. After the spring peak, there was anoccasional midsummer increase in beetle captures.This could be reßective of the extreme overlapping ingenerations for this species (Wood 1982). Major ßightactivity tapered off by August at all elevations.

A small number of D. ponderosae were captured inthis study. However, it is logical to conclude that D.ponderosae prefers higher elevation forests in this re-gion, because most captures occurred above 2,505 m.This corresponds with previous research in KaibabNational Forest, AZ, which reported heaviest infesta-tions occurring above 2,438 m (Blackman 1931). Inaddition to our results, previous studies also reportedlimited beetle presence in the ponderosa pine forests


near Flagstaff, AZ (Sanchez-Martinez and Wagner2002, McHugh et al. 2003, Gaylord et al. 2006). Withthe exception of the Kaibab Plateau in northern Ari-zona (Blackman 1931, USDA 2001Ð2004), its role inthe bark beetle community seems to be limited inArizona ponderosa pine forests. The highest elevationsite (2,651 m) comprised 66.0% of the 48D.ponderosaetrap catches. This site was located in a mixed conifertree stand on the San Francisco Peaks. The preferredhost forD. ponderosae in this part of Arizona seems tobe limber pine (USDA 2001Ð2004; J.D.M., unpublisheddata). Most D. ponderosae were captured from earlyAugust to early September, which corresponds withprevious reports on D. ponderosae ßight activity inponderosa pine forests (Blackman 1931, McCam-bridge 1964).

In this study, we used lure combinations that tar-geted three bark beetle species of concern (I. pini, I.lecontei, and D. brevicomis) in ArizonaÕs ponderosapine forests. Based on previous research in northernArizona (Gaylord et al. 2006), it was expected thatthese three lure combinations would also attract otherIps and Dendroctonus species. Therefore, these lureswere also used to describe the abundance and sea-sonality of three additional Ips and Þve additionalDendroctonus species. However, there are commer-cially available lure combinations targeting other spe-cies in this study that may facilitate a more thoroughdescription of the abundance and ßight seasonality ofsome bark beetle species in this region. While pher-omone traps are a widely used tool for monitoring barkbeetle abundance and ßight seasonality, some barkbeetle species experience temporal variation in re-sponse to their lures (Teale and Lanier 1991, Aukemaet al. 2000, Bentz 2006). This may impact the inter-pretation (i.e., estimating number of generations andßight seasonality) of pheromone trap results. Furtherstudy is needed to verify how the timing of pheromonetrap catches relates to beetle phenology and voltinismfor the bark beetle species in our region.

Efforts were made to cover the entire ßight period,but our study does not account for possible winterßight activity of bark beetles. In a previous study, I.piniwas the only bark beetle species captured duringthe winter months near Flagstaff, AZ, and then in onlyvery limited numbers (Gaylord et al. 2006). Theseresults suggest that ßight activity of bark beetles dur-ing the winter should not be a concern for resourcemanagers (Gaylord 2004). While this conclusion isapplicable for bark beetle ßight activity in the middleand high elevation bands of this study, the low eleva-tion band may experience more ßight activity duringmild winters. Zero trap catches were recorded forsuccessive weeks in late fall of 2005 and 2006 for allspecies except I. lecontei. However, temperatureswere frequently warm enough in January and Febru-ary 2006 (several weeks with maximum temperaturesabove 15�C) for some species, such as I. pini, to beßying.Further study isneeded todetermine theextentof winter ßight activity of species at elevations below1,736 m.

Temperature and Elevation. As expected, maxi-mum weekly temperatures were warmest at low ele-vation sites, and temperatures cooled as elevation in-creased (Fig. 13). SpeciÞc relationships betweentemperature and ßight data collected in this study andfrom Gaylord (2004) were analyzed by Gaylord et al.(2007). Based on weekly trap catch data and associ-ated maximum weekly temperatures, temperaturethresholds exceeding 15�C were estimated for springßight initiation for most bark beetle species, with theexception of D. adjunctus, which started ßying at14.5�C.

These results provide a physiological explanationfor the delay in spring ßight initiation for several spe-cies as elevation increases. For example, in 2006, tem-peratures were already �15�C during the Þrst collec-tion week at low and middle elevations, and beetlecaptures included I. pini, I. lecontei, I. calligraphusponderosae, D. frontalis, and D. brevicomis. Thresholdtemperatures were not reached until mid-April at highelevations, and therefore, ßight initiation of the afore-mentioned beetles did not occur until this time.

Flight cessation also seems to be affected by tem-perature differences across the elevation gradient. Asmaximum temperatures fell below threshold levels(15Ð21�C), bark beetle ßight activity tapered off. Tem-peratures cooled earlier in the year at high elevationsites. For example, in 2005, maximum temperaturesdeclined to threshold levels at least 1 mo earlier in thehigh elevation band than in the middle and low ele-vation bands. Accordingly, last captures ofD. frontalisand D. brevicomis occurred �1 mo earlier at highelevations. In 2006, maximum temperatures in all el-evation bands cooled below threshold levels within 2wk of each other, and ßight cessation ofD. brevicomisand D. frontalis occurred within the same amount oftime.

Flight initiation and cessation for some species, suchas D. valens, did not correspond well with thresholdtemperatures. For example, in 2006, when several spe-cies were ßying in March at low elevation sites (pre-sumably as a response to threshold temperatures beingexceeded),D. valenswas not captured until late April,within 1 wk of Þrst trap catches in the middle and highelevation bands. Also, D. valens ßight terminated be-fore temperature thresholds were met in the fall.These results suggest other environmental cues, or acombination thereof, may inßuence ßight activity ofcertain species.Dendroctonus adjunctus and I. knausihave distinctly

different seasonal patterns than the other beetles col-lected in this study, ßying mostly in the spring and fall.In addition, these two species have a lower tempera-ture threshold for ßight initiation and maintain ßightlonger in the fall than other Ips and Dendroctonus.Gaylord et al. (2007) suggested the lack of summerßight activity may be explained by a maximum tem-perature threshold or other environmental cue asso-ciated with bark beetle ßight.

According to our results, relatively small differencesin average maximum weekly temperatures (3Ð5�C)associated with elevation change inßuenced the tim-


ing and length of beetle ßight activity. These temper-ature differences could also play a role in the eleva-tional distribution of bark beetle species, because theability to survive cold winter temperatures may limitthe abundance of some bark beetles (Ungerer et al.1999, Lombardero et al. 2000), such as I. lecontei andD. frontalis, at higher elevations. This has implicationsfor climate change, where warming temperatures maynot only lengthen the period of ßight activity andincrease the number of generations per year, but alsoextend the range of abundant lower elevation barkbeetles to higher elevations (Bale et al. 2002, Williamsand Liebhold 2002), causing greater mortality toArizonaÕs ponderosa pine forests.

Acknowledgments

We thank C. Hayes, B. Loomis, T. S. Davis, A. Garcia,V. Bunker, G. Hancock, K. Baumgartner, E. Osborne, W.Winslow, M. Moreno, L. Smith, K. Murray, M. Schaffer, A.Somerville, J. Suby, and M. Trenam for Þeld and laboratoryassistance. A. Cognato and C. Allender aided in beetle iden-tiÞcation. Statistical advice provided by R. King is greatlyappreciated. We thank M. Gaylord, R. Hofstetter, and twoanonymous reviewers for manuscript review and critique.We thank the Coconino, Kaibab, and Tonto National Forestsfor permitting our work on public lands. This study wassupported by the 2004 United States Forest Service ForestHealth Protection Western Bark Beetle Research Initiative,and Agreement 03-JV-11221605-237 between the RockyMountain Research Station and Northern Arizona Univer-sity, and National Fire Plan Research Project 01.RMS.B.4.

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Received for publication 15 June 2007; accepted 1 October2007.


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