Semiochemical-mediated flight strategies of two invasive elm bark beetles: a potential factor in competitive displacement.

Abstract

A seven-state survey showed that the recently detected invasive Asian banded elm bark beetle, Scolytus schevyrewi Semenov, was abundant in areas of Colorado and Wyoming, whereas the long-established European elm bark beetle, S. multistriatus (Marsham), was not as abundant. In one of a series of studies to evaluate whether S. schevyrewi is competitively displacing S. multistriatus in their North American zone of sympatry, we characterized long-range flight responses infested or uninfested to small cut logs of American, Chinese, and Siberian elm, Ulmus americana, U. parvifolia, and U. pumila. Trials were conducted in Colorado and Wyoming to test the flight response of S. schevyrewi; in California to test the response of S. multistriatus; and in Nevada to test the responses of both species simultaneously. Studies with S. schevyrewi showed that males and females aggregated toward Ulmus spp. host volatiles but provided no evidence of a putative aggregation pheromone during the 0- to 48- or 48- to 96-h period of infestation. In contrast, S. multistriatus was attracted to U. pumila over unbaited controls, more to U. pumila infested with conspecific females than without, and more during the 48- to 96- versus 0- to 48-h period of infestation. This confirmed that male and female S. multistriatus aggregated toward host volatiles and that females produced an aggregation pheromone. In a cross-attraction study, S. schevyrewi displayed neither flight preference nor interruption to U. pumila infested with conspecifics, heterospecifics, or a mix of both species. Response of S. multistriatus was too low to draw conclusions. Although S. multistriatus aggregates moderately to host volatiles and strongly to female-derived pheromones emitted after a few days, S. multistriatus may have a relative disadvantage by selecting elm hosts more slowly than S. schevyrewi, which aggregates very strongly to host volatiles. The differential long-range host location strategy may be one factor in a chain of behavioral events that leads to advantageous host colonization and development by S. schevyrewi.

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CHEMICAL ECOLOGY
Semiochemical-Mediated Flight Strategies of Two Invasive Elm Bark
Beetles: A Potential Factor in Competitive Displacement
JANA C. LEE,1,2SHAKEEB M. HAMUD,2JOSE´F. NEGRO´N,3JEFFREY J. WITCOSKY,4
AND STEVEN J. SEYBOLD2
Environ. Entomol. 39(2): 642Ð652 (2010); DOI: 10.1603/EN09327
Aseven-statesurveyshowedthattherecentlydetectedinvasiveAsianbandedelmbark
beetle, Scolytus schevyrewi Semenov, was abundant in areas of Colorado and Wyoming, whereas the
long-established European elm bark beetle, S. multistriatus (Marsham), was not as abundant. In one
of a series of studies to evaluate whether S. schevyrewi is competitively displacing S. multistriatus in
their North American zone of sympatry, we characterized long-range ßight responses infested or
uninfested to small cut logs of American, Chinese, and Siberian elm, Ulmus americana, U. parvifolia,
and U. pumila. Trials were conducted in Colorado and Wyoming to test the ßight response of S.
schevyrewi; in California to test the response of S. multistriatus; and in Nevada to test the responses
of both species simultaneously. Studies with S. schevyrewi showed that males and females aggregated
towardUlmusspp.hostvolatilesbutprovidednoevidenceofaputativeaggregationpheromoneduring
the 0- to 48- or 48- to 96-h period of infestation. In contrast, S. multistriatus was attracted to U. pumila
over unbaited controls, more to U. pumila infested with conspeciÞc females than without, and more
during the 48- to 96- versus 0- to 48-h period of infestation. This conÞrmed that male and female S.
multistriatus aggregated toward host volatiles and that females produced an aggregation pheromone.
In a cross-attraction study, S. schevyrewi displayed neither ßight preference nor interruption to U.
pumilainfestedwithconspeciÞcs,heterospeciÞcs,oramixofbothspecies.ResponseofS.multistriatus
wastoolowtodrawconclusions.AlthoughS.multistriatusaggregatesmoderatelytohostvolatilesand
strongly to female-derived pheromones emitted after a few days, S. multistriatus may have a relative
disadvantage by selecting elm hosts more slowly than S. schevyrewi, which aggregates very strongly
to host volatiles. The differential long-range host location strategy may be one factor in a chain of
behavioral events that leads to advantageous host colonization and development by S. schevyrewi.
ABSTRACT
KEY WORDS
schevyrewi
aggregation pheromones, kairomones, Scolytidae, Scolytus multistriatus, Scolytus
Competitive displacement events warrant study for
their(1)appliedvalueofunderstandingenvironmen-
tal and economic impacts; (2) evolutionary insights
into speciation; and (3) ecological value as “natural
experiments” to study mechanisms of competition
(DeBach 1966). Such mechanisms can involve differ-
entialsearchingability,resourceacquisition,resource
preemption, fecundity, resource degradation, direct
physical agonistic interactions, reproductive interfer-
ence, intraguild predation, and susceptibility to nat-
ural enemies (reviewed by Reitz and Trumble 2002).
The displacement of one invasive species by another
represents 55% of the documented cases of competi-
tive displacement (Reitz and Trumble 2002). In a
well-studied case of two invasive cerambycid beetles,
PhoracantharecurvaNewmanwasobservedtoreplace
P. semipunctata F. in eucalyptus trees in southern
California in the 1990s (Bybee et al. 2004). From
experiments, replacement was likely mediated by the
preference of an egg parasitoid to oviposit on P. semi-
punctataeggsanditslowersurvivalratedevelopingon
P. recurva eggs (Luhring et al. 2004). However, many
cases of displacement have provided anecdotal evi-
dence of competition but lack empirical documenta-
tion or understanding of the mechanisms involved
(Simberloffetal.1997).TheNorthAmericaninvasion
of the Asian banded elm bark beetle, Scolytus
schevyrewi Semenov [(Coleoptera: Scolytidae) sensu
Wood (2007)], provides a timely opportunity to ex-
amine newly formed interspeciÞc interactions with
thelong-establishedEuropeanelmbarkbeetle,S.mul-
tistriatus (Marsham). These two bark beetle species,
which are allopatric in Eurasia, are now sympatric in
North America and both colonize the phloem of
1Correspondingauthor:USDAÐARS,HorticulturalCropsResearch
Laboratory, 3420 NW Orchard Ave., Corvallis, OR 97330 (e-mail:
jana.lee@ars.usda.gov).
2USDAForestService,PaciÞcSouthwestResearchStation,Chem-
icalEcologyofForestInsects,720OliveDr.,SuiteD,Davis,CA95616.
3USDA Forest Service, Rocky Mountain Research Station, 240
West Prospect Rd., Fort Collins, CO 80526.
4USDA Forest Service, Forest Health Management, 740 Simms St.,
Golden, CO 80401.

Page 2

AmericanandSiberianelm,UlmusamericanaL.andU.
pumila L. (Ulmaceae) (Negro ´n et al. 2005).
Scolytus multistriatus was Þrst detected a century
ago in North America (Chapman 1910) and now oc-
curs in most of the continental United States (Lee et
al. 2009). It has been a principal vector of Dutch elm
disease (Readio 1935) and the most serious bark bee-
tle affecting elm trees (Ohmart 1989). S. schevyrewi
was initially detected in 2003 in the United States
(Negro ´n et al. 2005) and is now known to occur in 28
U.S. states (Lee et al. 2009) and in southern Alberta,
Manitoba, Ontario, and Saskatchewan in Canada
(CFIA 2007, Langor et al. 2009). S. schevyrewi colo-
nizes stressed elms (Shi and Chen 1990), causes tree
mortality (Negro ´n et al. 2005), and may vector one of
the fungal species that causes Dutch elm disease,
Ophiostoma novo-ulmi (Jacobi et al. 2007). Despite
their co-occurrence and the potential for confusion,
the two bark beetle species are readily separated by
external morphological characters, even by the non-
specialist (Negro ´n et al. 2005). A seven-state survey
for both beetles was conducted around Sacramento,
CA; Reno, NV; Ogden, UT; Newcastle, WY; Fort Col-
linsandDenver,CO,in2006Ð2007,andinManhattan,
KS, and Columbia, MO, in 2007 (Lee et al. 2009).
Abundance of S. schevyrewi relative to total Scolytus
capturedwas90and89%inColoradoin2006and2007,
respectively.Relativeabundanceinbothyearswas90
and 83% in Wyoming, 60 and 68% in Utah, 43 and 68%
in Nevada, 11 and 13% in California, 3.3 in Kansas
(2007), and 2.7% in Missouri (2007).
We have hypothesized that the high incidence of S.
schevyrewi and low incidence of S. multistriatus in
some areas of the United States may be the result of
S. schevyrewi competitively displacing S. multistriatus
(Lee et al. 2009, Lee and Seybold 2010). A reduction
in S. multistriatus population density seems to have
occurred in Colorado since S. multistriatus was recov-
eredinthethousandsfromelmlogsinthe1970sinFort
Collins and Denver (Hostetler and Brewer 1976). In
2003, S. multistriatus was recovered as only 1 and 13%
ofScolytusspp.emergingfromelmlogsinFortCollins
and ßying into baited funnel traps in Denver, respec-
tively (Negro ´n et al. 2005). In 2006 and 2007 in Fort
CollinsandDenver,S.multistriatusaccountedfor10Ð
11% of Scolytus spp. detected in surveys with baited
funnel traps, unbaited Plexiglas traps, and trap logs
(Lee et al. 2009). Similar declining trends of S. mul-
tistriatus and increasing trends of S. schevyrewi have
been observed in Reno, NV. In 2003, S. multistriatus
represented 88.6% of emerging Scolytus beetles from
elmlogs(Negro ´netal.2005),andthenat57%in2006,
and32%in2007fromthethreetrappingmethods(Lee
et al. 2009). Changes in S. multistriatus population
densities may also be caused by environmental
changes, differential rates of parasitism or predation,
or other causes. Thus, longer-term surveys would val-
idate the competitive displacement of S. multistriatus
by S. schevyrewi.
Evaluationofthepotentialforcompetitivedisplace-
ment of S. multistriatus involves an examination of
long- and short-range behavioral events that occur
during bark beetle host colonization (Wood 1982,
Graves et al. 2008), as well as any differential aspects
of development that occur at points in the life cycle
after the establishment phase of host colonization
(Light et al. 1983). Investigation of semiochemical-
mediated host location strategies may elucidate ad-
vantageouslong-rangeßightbehaviorsinS.schevyrewi
in the earliest phases of host colonization. Later, fol-
lowing host location, potential components in the
mechanism of competitive displacement may include
differential host acceptance, oviposition, and larval
development when the two species are on or below
the bark surface (Lee and Seybold 2010). Differences
in fecundity, generation time, and emergence period
could also provide S. schevyrewi with an advantage or
disadvantagecomparedwithS.multistriatus(Table1),
but these parameters have yet to be substantiated
under controlled conditions. Differences in genera-
Table 1.Life history attributes for S. schevyrewi and S. multistriatus
Attribute S. schevyrewi (new invasive)S. multistriatus (established invasive)
Eggs per female
Developmental time
20Ð120 eggs in Chinaa
30 d in Coloradoc
40Ð45 d in Chinaa
Pupae in Chinaa
9Ð86 eggs in laboratoryb
35Ð40 d in eastern United Statesd
?60 d in Coloradoe
Larvae in eastern United Statesdand Coloradoe
Overwintering stage
Initial seasonal ßight
Californiaf
Nevadaf,g
3Ð9 Apr. 2007
7Ð23 Apr. 2004
22Ð27 Apr. 2005
5Ð11 Apr. 2007
22 Mar.Ð5 Apr. 2004 (Jefferson Co.)
14Ð22 Apr. 2004 (Larimer Co.)
31 Mar.Ð7 Apr. 2004 (Weld Co.)
31 Mar.Ð7 Apr. 2005 (Larimer Co.)
14Ð19 Apr. 2005 (multiple counties)
20Ð27 Apr. 2006 (Jefferson Co.)
31 Mar.Ð7 Apr. 2006 (Larimer Co.)
21Ð28 Apr. 2006 (Weld Co.)
2Ð3 in Chinaa
3Ð9 Apr. 2007 (in same traps)
7Ð23 Apr. 2004
4Ð26 May 2005
5Ð11 Apr. 2007
12Ð19 Apr. 2004
14Ð22 Apr. 2004
21Ð28 Apr. 2004
4Ð12 May 2005
5Ð11 May 2005
18Ð25 May 2006
28 Apr.Ð4 May 2006
19Ð26 May 2006
2, partial third generation in Californiai
Coloradof,h
Generations per year
aWang (1992);bCannon (1985);cNegro ´n et al. (2005);dBaker (1972);eCranshaw et al. (1993);fLee et al. (2009);gLee et al. (unpub-
lished data);hNegro ´n et al. (unpublished data); andiBrown (1965).
April 2010LEE ET AL.: FLIGHT BEHAVIOR OF ELM BARK BEETLES
643

Page 3

tion time and emergence period might be inferred
fromcomparisonsofseasonalßightactivityofthetwo
species,butmeasurementofthisactivitymightalsobe
inßuenced by the abundance of the two species in a
given area. From limited and preliminary ßight trap
catch data recorded in March, April, and May, S.
schevyrewi seems to ßy earlier than S. multistriatus
(Table1,oneofthreestudiesinNevada;sevenofeight
studies in Colorado). However, in one case in Cali-
forniaandtwocasesinNevada,theinitialßightofboth
species was concurrent (Table 1).
Inthisstudy,weinvestigatedthelong-rangeaspects
of host colonization behavior that may impart a com-
petitiveadvantageforS.schevyrewi.OurÞrstobjective
was to compare the relative ßight attraction of S.
schevyrewi and S. multistriatus to U. americana and to
U.pumila.GiventhatS.schevyrewiandU.pumilashare
the same native range in Asia (Michalski 1973, Moore
2003), S. schevyrewi may be better adapted than S.
multistriatus to locate and colonize U. pumila. The
incidence of S. schevyrewi in the United States has
beenassociatedanecdotallywithmarkedlyhigherlev-
els of U. pumila mortality in the western Great Plains
(Negro ´n et al. 2005, Lee et al. 2006). Our second
objectivewastocomparetheresponsesofbothbeetle
species to host elm (i.e., kairomone) volatiles and
beetle-produced (i.e., pheromone) volatiles, and the
timing of potential pheromone production. The pher-
omone biology of S. multistriatus has been studied in
the United States the 1970s (Lanier et al. 1976), but
information is lacking on the pheromone biology of S.
schevyrewi.Aspeciesthataggregatesstronglytopher-
omonesrelativetokairomonesmayhaveanadvantage
but is also limited by the timing of the initiation of
pheromone production, which might delay aggrega-
tion. Our third objective was to determine how each
species responded to heterospeciÞc cues because a
differential response might lead one species to locate
hosts more rapidly. A species that is cross-attracted to
volatiles associated with hosts attacked by heterospe-
ciÞcs might Þnd more reproductive opportunities
(Birchetal.1980).Similarly,aspeciesthatavoidshosts
with heterospeciÞcs, even though conspeciÞcs are
also present, would miss opportunities to mate with
availableconspeciÞcsandhavefewerresourcestouse
locally (Birch and Wood 1975). Although an inter-
ruptive (allomonal) response to heterospeciÞcs may
be adaptive to avoid competition (Birch and Wood
1975,ByersandWood1980,Byers1993),theevolution
of this response will be important to understand the
host colonization behavior and ultimately the success
of each beetle species.
Materials and Methods
The ßight responses of S. schevyrewi and S. multi-
striatus to Ulmus spp. were evaluated in Þve experi-
mentsinthewesternUnitedStates.Inallexperiments,
freshly cut pieces of Ulmus branches and stems were
obtained from private property and municipal tree
removals (Table 2) and were stored at 8?C until they
were cut into smaller test logs (bolts hereafter). Also,
largeinfestedU.pumilalogswerecollectedfromÞeld
sites known to have high populations of Scolytus spp.
(Table 2). These logs were placed into large rearing
boxes (Browne 1972), and newly emerged (within 1
wk)adultS.schevyrewiorS.multistriatuswereusedin
each experiment.
Inexperiment1,theßightresponseofS.schevyrewi
was tested in Colorado and Wyoming where this spe-
cies is abundant (Lee et al. 2009) (treatments, dates,
and locations in Table 2). The objectives were to
compare the host preference of S. schevyrewi for U.
americana or U. pumila and determine the ßight re-
sponse to pheromonal and/or kairomonal cues by
comparing elm hosts with and without female S.
schevyrewi. Freshly cut bolts (?11 cm long by 9 cm
diameter) were placed into separate mesh fabric bags
16 h before placement in the Þeld and kept indoors at
ambient room temperature. For one half of the bolts,
25 female S. schevyrewi were released onto the bolt so
that they could bore into the elm, feed, and possibly
produce pheromones. After 16 h, the four types of
bolts (treatments) were each hung next to the mid-
point of a separate 12-unit Lindgren funnel trap
(Lindgren 1983) and traps were spaced at least 20 m
apart;anunbaitedtrapservedasacontrol.Treatments
were set up in four blocks, collections were made
daily,andboltswereremovedeachtimethatthetraps
were emptied. Replacement bolts were placed on the
same traps and the traps were rerandomized in posi-
tionduringeachreplicationovertime.Oldboltswere
debarked, and the number of females that had con-
structed galleries was recorded. Similar protocols
wereusedinexperiments2Ð5(below),exceptthatthe
amount of time that beetles were allowed to infest
bolts before placement in the Þeld, and the trapping
intervals varied (Table 2). All experiments tested the
ßight response of these Scolytus spp. with cut bolts
because both species have been frequently observed
to locate and develop in cut stem sections, broken
limbs, or dying elms in the Þeld. Experiments with
living elms might yield different results because of in-
ducedplantresponsesthatmayimpactplantvolatileand
beetle pheromone production. These more complex
phenomena were not examined in our experiments.
In experiment 2, the ßight response of S. multistria-
tus was tested in California, where this species is rel-
ativelyabundant.Theobjectivesweretocomparethe
host preference of S. multistriatus for U. americana, U.
parvifolia,andU.pumila,andtodeterminetheattrac-
tion to pheromone and/or kairomonal host cues by
comparing the ßight responses to elm hosts with and
withoutfemaleS.multistriatus.Boltswerepreparedas
in experiment 1, but with female S. multistriatus in-
festing U. americana and U. pumila. Newly emerged
females collected from the rearing box were presum-
ablyunmatedandusedbecauseelmsinfestedbyvirgin
female S. multistriatus are known to be highly attrac-
tive to conspeciÞcs in the Þeld (Peacock et al. 1971).
Most emerging female S. multistriatus and S.
schevyrewi were considered to be unmated because
they could make nuptial chambers, but did not exca-
vateegggallerieswhenplacedontonewelmswithout
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Vol. 39, no. 2

Page 4

conspeciÞcmales(unpublisheddata).Chineseelm,U.
parvifolia, was also tested because it is a frequently
planted elm in California landscapes and sometimes
attacked by S. multistriatus (Sˇvihra 1998). However,
because of the limited amount of U. parvifolia avail-
ableandthedifÞcultyofgettingS.multistriatustobore
into this host (unpublished data), U. parvifolia was
only tested alone and not as a beetle-infested bolt.
In experiment 3, the ßight response of S. multistria-
tuswastestedagaininCalifornia.Theobjectivewasto
determine how the timing of infestation would affect
ßight response of S. multistriatus. A wider interval of
infestationwastestedbecausepheromoneproduction
among unmated female S. multistriatus was known to
increase by the third day under laboratory conditions
(Peacock et al. 1973). Two days before placement in
the Þeld, freshly cut U. pumila bolts were placed in
mesh bags. One third of the bolts were uninfested
controls, a second third of the bolts initially received
females, and the Þnal third of the bolts received fe-
males as they were placed in the Þeld, such that bolts
exposed in the Þeld contained females releasing vola-
tiles during the 48- to 96- or 0- to 48-h period of
infestation, respectively.
Table 2.
and Wyoming (WY)
Field experiments of the flight behavior of S. schevyrewi and S. multistriatus in California (CA), Colorado (CO), Nevada (NV),
ExperimentTreatments Trapping datesLocations
1Unbaited
U. americanaa
U. pumila
U. americana, 25 ? S. schevyrewi 16Ð40 h
(4.6 ? 0.5 beetles that constructed
galleries in test logs established by
post-exp dissection of logs)
U. pumila, 25 ? S. schevyrewi 16Ð40 h
(14.9 ? 0.9)
11Ð21 July 2006
8 collections
1-d trapping intervals
Larimie Co., WY, Cheyenne East High School,
41?08Õ57“N, 104?46Õ 37”W
Larimer Co., CO, Colorado State University
Experimental Station, 40?39Õ28“N, 104?59Õ49”W
Larimer Co., CO, elm lot in Fort Collins, 40?33Õ54“N,
105?04Õ43”W
Jefferson Co., CO, Lakewood Federal Center,
39?43Õ12“N, 105?06Õ58”W
2Unbaited
U. americanab
U. pumila
U. americana, 25 ? S. multistriatus 16Ð64
h (17.9 ? 0.7)
U. pumila, 25 ? S. multistriatus 16Ð64 h
(19.8 ? 0.5)
U. parvifolia
16 Aug. to 8 Sep.
2006
Eight collections
2-d intervals
Yolo Co., CA, Woodland residence, 38?40Õ20“N,
121?45Õ35”W
Yolo Co., CA, Davis laboratory, 38?32Õ21“N, 121?44Õ21”W
Yolo Co., CA, UC Davis tree disposal yard, 38?32Õ01“N
121?48Õ42”W
Sacramento Co., CA, Bing Maloney Golf Course,
38?30Õ08“N, 121?29Õ36”W
3Unbaited
U. pumilac
U. pumila, 25 ? S. multistriatus 0Ð48 h
(13.6 ? 0.7)
U. pumila, 25 ? S. multistriatus 48Ð96 h
(16.8 ? 0.6)
6 June to 3 Aug.
2007
11 collections
unbalanced
2-d intervals
Same as experiment 2
4 Unbaited
U. pumilad
U. pumila, 25 ? S. schevyrewi 0Ð48 h
(15.4 ? 1.3)
U. pumila, 25 ? S. schevyrewi 48Ð96 h
(18.0 ? 0.9)
U. pumila, 13 ? S. schevyrewi 0Ð48 h, 13
? S. schevyrewi 48Ð96 h (17.1 ? 0.8)
5Ð19 July 2007
7 collections
2 d intervals
Larimie Co., WY, Cheyenne East High School
(2 blocks), 41?08Õ57“N, 104?46Õ37”W
Larimer Co., CO, Colorado State Forest Service
nursery, 40?35Õ15“ N, 105?08Õ36”W
Larimer Co., CO, elm lot in Fort Collins, 40?33Õ54“N,
105?04Õ43”W
5 Unbaited
U. pumilae, 25 ? S. multistriatus 24Ð96 h
(14.5 ? 0.8)
U. pumila, 25 ? S. schevyrewi 24Ð96 h
(17.4 ? 0.9)
U. pumila, 25 ? S. multistriatus (14.2 ?
0.9), 25 ? S. schevyrewi 24Ð96 h
(17.3 ? 0.9)
25 JulyÐ18 Aug. 2007
Eight collections
3-d intervals
Washoe Co., NV, Equestrian Center, 39?32Õ28“N
119?48Õ20”W
Washoe Co., NV, Idlewild Park, 39?31Õ18“N 119?49Õ59”W
Washoe Co., NV, City tree yard, 39?31Õ12“N
119?46Õ15”W
Washoe Co., NV, Brookside Golf Course, 39?30Õ03“N
119?45Õ44”W
aUninfested U. pumila and U. americana collected on 19 and 27 June 2006, respectively, from Washoe Co., NV, and stored at 8?C for 30 d;
S. schevyrewi emerging within 1 wk before the experiment was reared from infested U. pumila collected in June 2006 from Jefferson Co., CO.
bUninfested U. parvifolia collected in Aug. 2006 from Sacramento Co., CA, whereas the other two infested elm bolts were collected as
described in experiment 1 but were stored at 8?C for 60 d; S. multistriatus was reared from infested U. pumila collected in Aug. 2006 in Yolo
Co., CA.
cUninfested U. pumila collected on 8 Mar. 2007 from Washoe Co., NV, and stored at 8?C for 90Ð120 d; S. multistriatus was reared from a
laboratory colony started from infested U. pumila collected on 20 Sept. 2006 in Washoe Co., NV.
dUninfested U. pumila collected on 29 Mar. 2007 from El Paso Co., CO, and stored at 8?C for 120 d; S. schevyrewi was reared from infested
U. pumila collected in June 2007 in Jefferson Co., CO.
eUninfested U. pumila collected as described in experiment 3 but stored at 8?C for 120Ð150 d; S. multistriatus was reared from infested U.
pumila collected in June 2007 in Yolo Co., CA; S. schevyrewi was reared from infested U. pumila collected on 5 June 2007 in Washoe Co., NV.
April 2010LEE ET AL.: FLIGHT BEHAVIOR OF ELM BARK BEETLES
645

Page 5

Inexperiment4,theßightresponseofS.schevyrewi
was tested again in Colorado and Wyoming. The ob-
jective was to compare the response of S. schevyrewi
to test bolts of U. pumila infested by conspeciÞcs for
0Ð48 and 48Ð96 h. An additional treatment of male-
infested bolts was included because the pheromone
and mating habits of S. schevyrewi are not well under-
stood. For the treatment with the male-infested bolt,
13 male S. schevyrewi were released onto the bolt
during the initial preparation, and another 13 males
were released onto the same bolt as it was placed
outside. Because elm bolts were a limited resource at
the time, this treatment was prepared to release vola-
tiles speciÞc to males during the 0- to 48-h, as well as
the 48- to 96-h period of infestation.
Inexperiment5,theßightresponsesofS.schevyrewi
andS.multistriatusweretestedinReno,NV,wherein
2006 both species had been found to co-occur in rel-
atively similar abundances (Lee et al. 2009). The ob-
jective was to simultaneously compare both S.
schevyrewi and S. multistriatus attraction or interrup-
tion to bolts infested with con- and heterospeciÞcs.
Each treatment received two U. pumila bolts kept in
separate mesh bags: (1) uninfested bolt, bolt with 25
female S. schevyrewi; (2) uninfested bolt, bolt with 25
female S. multistriatus; (3) bolt with 25 female S.
schevyrewi and bolt with 25 female S. multistriatus; or
(4) unbaited control. Females were released onto the
bolts 24 h before placement in the Þeld for 3 d and
hence exposed at 24Ð96 h of infestation. Bolts in-
fested by both Scolytus species were stored sepa-
ratelyuntilplacementintheÞeldincasethespecies
would interact and change their volatile production
in each otherÕs presence. Hypothetically, if one spe-
cies avoided hosts infested by heterospeciÞcs, the
numbers of beetles captured in the conspeciÞc
treatment would be higher than those captured in
the mixed species treatment.
To compare ßight responses to the treatments, the
number of male and female S. schevyrewi and S. multi-
striatus captured per trap was transformed by log10(x ?
1)tohomogenizevariances.Foreachsexandspecies,
an analysis of variance (ANOVA) was used to test for
the signiÞcance of block, treatment, replication over
time (rep), and treatment ? rep on trap catches in
PROC GLM (SAS Institute 2001). If the effect of
treatment was signiÞcant at the level of ? ? 0.05,
treatment means over the sampling period were com-
pared by using RyanÕs Q multiple comparison, which
has more power (1 ? ?) while reducing the proba-
bility of experimentwise type I error (Day and Quinn
1989). No S. multistriatus were captured in experi-
ments1and4inColoradoandWyoming.Becauseless
than two beetles were captured per trap per interval
in some experiments, both sexes of S. schevyrewi were
combined for analyses in experiments 2 and 3 and
combined for S. multistriatus in experiment 5.
Voucher specimens have been deposited at the Or-
Table 3.
Nevada, and Wyoming in 2006–2007
ANOVA results for field experiments of the flight responses of S. schevyrewi and S. multistriatus in California, Colorado,
ExperimentSpecies Effectdf
MalesFemales
FPFP
1S. schevyrewiBlock
Treatment
Replication over time
Treatment ? replication
Block
Treatment
Replication
Treatment ? replication
Block
Treatment
Replication
Treatment ? replication
Block
Treatment
Replication
Treatment ? replication
Block
Treatment
Replication
Treatment ? replication
Block
Treatment
Replication
Treatment ? replication
Block
Treatment
Replication
Treatment ? replication
Block
Treatment
Replication
Treatment ? replication
3, 117
4, 117
7, 117
28, 117
3, 129
5, 129
7, 129
35, 129
3, 129
5, 129
7, 129
35, 129
3, 97
3, 97
12, 97
36, 97
3, 97
3, 97
12, 97
36, 97
3, 102
4, 102
6, 102
24, 102
3, 93
3, 93
7, 93
21, 93
3, 93
3, 93
7, 93
21, 93
12.6
41.0
7.6
1.2
4.85
6.52
0.70
0.81
8.1
7.3
1.0
0.86
8.08
2.35
3.20
1.12
42.5
11.7
3.75
0.73
2.42
60.8
2.00
1.22
22.0
69.1
7.8
1.43
9.79
12.4
1.93
1.57
?0.001
?0.001
?0.001
0.28
0.003
?0.001
0.672
0.76
?0.001
?0.001
0.41
0.69
?0.001
0.077
?0.001
0.326
?0.001
?0.001
?0.001
0.86
0.07
?0.001
0.073
0.24
?0.001
?0.001
?0.001
0.13
?0.001
?0.001
0.073
0.074
17
48
10
1.4
Both sexes pooled
?0.001
?0.001
?0.001
0.12
2S. schevyrewi
S. multistriatus 10.8
10.2
0.9
0.80
Both sexes pooled
?0.001
?0.001
0.51
0.77
3S. schevyrewi
S. multistriatus 40.5
12.1
5.12
0.68
4.28
62.9
2.99
1.16
16.5
66.3
6.47
1.61
Both sexes pooled
?0.001
?0.001
?0.001
0.91
0.007
?0.001
0.01
0.30
?0.001
?0.001
?0.001
0.063
4S. schevyrewi
5S. schevyrewi
S. multistriatus
646ENVIRONMENTAL ENTOMOLOGY
Vol. 39, no. 2