Host preference by Saperda calcarata Say (Coleoptera: Cerambycidae)

2005·4.5 MB·English

by  Cynthia L Broberg

J.Entomol. Soc. Brit. Columbia 102,December2005 27
Host preference by Saperda calcarata Say
(Coleoptera: Cerambycidae)
CYNTHIA L. BROBERG^ and JOHN H. BORDEN^ ^
ABSTRACT
We conducted five laboratory and one field experiments to examine potential host selec-
tion mechanisms of Saperda calcarata Say in British Columbia. Olfactory bioassays
indicated that female (and possibly male) beetles were attracted to volatiles from leafy
twigs of trembling aspen, Populus tremuloides Michaux. However, wounding of the
bole, ethanol baiting, orboth, did not result in significant orientation toward or attack of
trembling aspens in the field. Feeding preferences for trembling aspen were strong for
both sexes in choice bioassays, but in no-choice bioassays, females did not discriminate
between trembling aspen and black cottonwood, P. trichocarpa Torrey & Gray.
Scouler's willow, Salix scoideriana Barrat in Hooker, was fed upon the least by both
sexes. When diameter ofbolts offered as oviposition hosts was equalized, frequency of
oviposition was similar among the three hosts. Our data suggest that feeding preference
is thepredominant mechanism ofhost selectionby S. calcarata.
INTRODUCTION
The poplar borer, Saperda calcarata a short period of maturation feeding
Say (Coleoptera: Cerambycidae: Lamiinae) (Linsley 1959) and mate. Females oviposit
attacks living poplars from the sections into oblong niches chewed in the bark of
Populus {P. tremuloides Michaux, P. alba host trees. Young larvae mine in the inner
L.,P. grandidentata Michaux), Aigeiros {P. bark and sapwood, then move deeper creat-
deltoides Bartram, P. fremontii Watson, P. ing large, irregular galleries throughout the
nigra L. 'Italica'), and Tacamahaca {P. sapwood and heartwood (Hofer 1920). Fre-
angustifolia James, P. balsamifera L., P. quently a single tree is repeatedly attacked
&
trichocarpa Torrey Gray) throughout forming a 'brood' tree. Attacked trees are
their range in North America (Hofer 1920, identified by their deformed bole, oviposi-
Baker 1972, Drouin & Wong 1975, Ne- tion scars, sap stains spreading down the
beker et al. 1985). The beetle also attacks bark, and frass piles at their base. The life
poplar hybrids {P. x acuminata) (Hofer cycle takes three to four years in Canada,
1920) and willows (Baker 1972). Populus but is probably shorter in the south (Hofer
spp. are susceptible from approximately 1920, Peterson 1947, Baker 1972).
three years of age (Abrahamson & Saperda calcarata is considered a major
Newsome 1972), or 4-5 cm diameter at pest of poplars (Solomon 1987) and fre-
breast height (dbh = 1.3 m) (Hofer 1920, quently becomes prevalent within stands
Drouin & Wong 1975, Nebeker et al. (Bird 1930, Nebeker et al. 1985). Physical
1985). Saperda calcarata adults reportedly damage to the boles from larval galleries
discriminate amongpoplarhybrids for feed- makes trees susceptible to breakage. Open-
ing (Garland & Worden 1969) and there are ings from oviposition niches and wood-
differences in attack rates among P. del- peckers lead to increased incidence of
toides clones (Nebeker etal. 1985). pathogens like Hypoxylon mammatum
In British Columbia (BC), S. calcarata (Wahlenberg) Karsten (Graham & Harrison
adults emerge in late June to July, undergo 1954) or Phellinus tremulae (Bondartsev)
^DepartmentofBiological Sciences, SimonEraserUniversity, Bumaby,BC, V5A 1S6,Canada
'CurrentAddress: PheroTechInc., 7572ProgressWay,Delta, BC, V4G 1E9
28 J.Entomol. Soc.Brit.Columbia 102,December2005
&
Bondartsev Borisov (Hofer 1920) which brood trees were larger and faster growing
girdle the bark or stain and rot the wood, than neighbouring trees, and Abrahamson
and attacked trees may be further damaged & Newsome (1972) concludedthere was no
by other insects, e.g., Agrilus anxius Gory difference in attack level on different qual-
or Poecilonota cyanipes (Say) (Hofer ity sites. Olfaction is generally believed to
1920). play a large role in cerambycid host loca-
Because attacks by beetles may be tion (Linsley 1961, Hanks 1999, Allison et
prevalent in poor sites, e.g., dry slopes al. 2004).
(Hofer 1920, Bird 1930, Morris 1963), or in We commonly observe S. calcarata
decadent hosts (Graham & Harrison 1954), attack in trembling aspen,P. tremidoides, in
S. calcarata is assumed to prefer weakened BC, but not in black cottonwood, P. tricho-
hosts that remain alive during attack (Hanks carpa, or willow, Salix spp. Our objectives
1999). In agreement with this hypothesis, were to determine: if olfactory attraction
less attack was observed on P. deltoides occurs to trembling aspen, the apparent
clones from southern provenances which preferred host, and if there are different
grew most vigorously (Nebeker et al. levels of feeding or oviposition among
1985). In contrast, Baker (1972) noted that these three hosts.
MATERIALS AND METHODS
Saperda Colonies. We collected ca. 2.5 gated in the laboratory using a still air ol-
m^ S. calcarata-aiiSLckQd trembling aspen factometer (Figure 1). Randomly assigned
bolts from trees felled near 70 Mile House, treatment and controljars contained either a
BC in April orMay of2002 to 2004. Aduhs smalljarofwaterwith a small, leafy branch
emerged from the caged bolts during June of aspen, or just water, respectively. The
andJuly fortwo successive years. A total of arena ceiling was a sheet of clear Lexan
76 and 101, 46 and 30, and 11 beetles (GE Polymershapes, Coquitlam, BC). A
emerged each year from bolts harvested in video camera was positioned above the
2002, 2003 and 2004, respectively. Timing arena. To induce the photopositive beetles
of emergence was in agreement with Gar- to approach the stimuli, a fluorescent light
land & Worden (1969). Aduhs were kept was placed under the platform between the
on aspen branches in water in 1.2 x 1.8 x two jars. The entire apparatus was covered
m
0.6 outdoor enclosures until used in bio- with a black cloth. Three to five adults ofa
assays. Beetles were used once in any one single sex taken directly from the holding
type ofbioassay, except for feeding bioas- cage were placed into each arena. Presence
says in 2002, when tested beetles were re- ofbeetles in the concentric rings above the
turned to the holding cage from which test treatment or controljars were determined at
subjects were removed. 30 sec intervals for2 h. Fourteentrials were
Plant material. Leafy aspen branches recorded. Feeding damage to the perforated
were collected periodically, mostly from centres above control and treatment stimuli
various interior BC locations, but also from was assessed for both recorded and unre-
Bumaby and Maple Ridge on the coast. corded trials. Jars were washed and the pa-
Branches were kept with the cut ends in per covering replaced before each assay.
water at 4 °C, and used in bioassays within Assays commenced any time between 0800
one week. Both Scouler's willow, Salix and2400 h.
scouleriana Barrat in Hooker, and black A field experiment was set up in a trem-
cottonwoodbranches were collected in Bur- bling aspen grove near Sabiston Lake,
naby, BC the same day bioassays were per- northeast ofSavona, BC, on 28 June, 2002.
formed. In total, four to five genotypes of Apparently healthy trees, spaced approxi-
m
each species were tested. mately 20 apart, received one of four
Olfaction experiments. In 2003 and treatments in a randomized block design (n
2004, responses to volatiles were investi- = 14): 4 axe cuts on opposite sides of the
J.Entomol. Soc.Brit. Columbia 102,December2005 29
Figure 1. Schematic ofolfactometer used to test olfactory responses ofS. calcarata to trem-
bling aspen leafvolatiles. A 60 cm diameter circular arena consisted ofa black cylinder 60 cm
high (A) placed on a white coroplast (GE Polymershapes, Coquitlam, BC)platfonn (C) with two
holes, 5.5 cm in diameterwith centres 28 cm apart. This platform was covered with white paper
(B)perforated41 timeswithapin inauniform, radial pattern above the openings. Three concen-
tric rings 5.5, 12.5, and 19.5 cm diameter were drawn on the paper (B) above each hole. The
platform(C) restedon glass cookiejars (aperture 11 cm diameter) (D), centred below each hole.
tree at ca. 1.5 m; ethanol bait stapled at ca. choice bioassays contained one ofthe three
2 m; 4 axe cuts plus ethanol bait; or no potential hosts, and choice bioassays con-
treatment. Ethanol is a ubiquitous kairo- tained one branch ofeach. Before an assay,
monal indicator ofstressed trees (Kelsey & the leaves were traced onto paper. After the
Joseph 1998 and references therein). The bioassay ended, leaves were attached to
m
basal 3 of the trees were examined for their traced counterparts, scanned, and the
oviposition in 2003 and 2004. leaf area consumed was quantified using
Feeding bioassays. Choice and no- Scion Image software (Scion Corporation,
choice feeding bioassay experiments were Frederick, Maryland). A total of 17 choice
performed to investigate feeding prefer- and 14 no-choice bioassays were performed
ences of S. calcarata among trembling as- during July of2002 and 2003.
pen, black Cottonwood and Scouler's wil- Oviposition bioassays. In 2002 we
low. Three small branches, each with three tested oviposition by S. calcarata in hold-
to five leaves, were placed in water-filled ing cages on eight freshly cut bolts ofvary-
vials inside 17x16x12 cm plexiglass boxes. ing diameter ofeach ofthe above three spe-
A
single S. calcarata adult was allowed to cies. In 2003, two apparently healthy trem-
freely feed on plant material overnight. No- bling aspen, black cottonwood, and
30 J. Entomol. Soc. Brit. Columbia 102, December2005
Scouler's willow trees of similar diameter than controljars. Chi-square tests were per-
were felled on 1 and 18 July 2003, bucked formed for each sex to compare the fre-
and transported to SFU where they were quency offeeding damage above treatment
kept refrigerated until needed. Six to eight v^'. control stimuli against the null hypothe-
beetle pairs were placed in 13 outdoor sis of no discrimination between stimuli.
cages, 90 X 90 X 90 cm, with one randomly Data from feeding and oviposition bioas-
positionedbolt ofeach species and a central says were transformed by x ' and log(x+l),
water jar containing leafy trembling aspen respectively, to correct for non-normality
branches for seven days. Bolts were ca. 50 and heteroskedasticity, then analyzed as
cm in length, and diameters taken from randomized complete blocks by ANOVA
their midpoint. Oviposition was determined with PROC GLM (SAS Institute 1990).
in both experiments by opening all niches Because it was not possible to perform all
cut in thebark. no-choice feeding assays at the same time,
Statistical analyses. In all cases a = the analysis included trial date and host
0.05. For olfaction bioassays, one-tailed species effects. The final model did not
paired t-tests were used to determine ifthe include interaction effects. Multiple com-
REGWQ
frequency of observations in each of the parisons were performed with
concentric rings was greater over treatment (SAS Institute 1990).
RESULTS
Olfaction experiments. There were no Garland & Worden (1969), but only quanti-
differences in the occurrence of beetles in fied the more abundant foliar damage.
the middle and outside rings bordering the When given a choice (Figure 2), both sexes
perforated area above treatment (i.e. trem- clearly preferred trembling aspen over both
bling aspen leaves) and control stimuli for black Cottonwood and Scouler's willow
both sexes (middle ring, females, t = 0.69, (females F2.32 = 41.15, P < 0.0001; males
P = 0.26, males, t = -0.80, P = 0.23; outer ^2,32 = 42.68, P < 0.0001). There were also
ring, females, t = 0.76, P = 0.24, males, t = significant differences in feeding in the no-
0.95, P = 0.19). Females (but not males) choice experiment (females F2,34 = 20.53, P
were present more frequently above the < 0.0001; males F2,33 = 26.96, P < 0.0001).
treatment than the control stimulus (Table However, females acceptedtrembling aspen
1). Often, females and males fed on the and black cottonwood equally, and males
perforated paper directly above the treat- fed on black cottonwood more vigorously
ment stimulus, but in one instance females than on Scouler's willow (Figure 2).
fed above the control as well (Table 1). Oviposition bioassays. When bolt di-
Females also chewed curvilinearpatterns in ameter was not controlled in 2002, S. cal-
the paper covering the arena floor that were carata females oviposited preferentially in
reminiscent of oviposition niches, but no trembling aspen and black cottonwood, the
eggswere found. species with the largest diameter bolts
Very few attacks were found on trem- (Table 2). When bolt diameter was equal-
bling aspen treated to release host volatiles ized in 2003, there was no preference in
(axe cuts) or baited with ethanol. A total of oviposition among the three host species
8 oviposition chambers in two replicates (Table 2).
were found: 1 niche on an ethanol-treated We observed some larvae feeding in the
tree; 1 and 3 niches on two axe-cut trees; 2 bark of all three species, but they did not
and 1 niches on two trees with both treat- survive long as bark quality deteriorated
ments and none on control trees. None of rapidly because of infection by Cytospera
these niches developed into successful lar- chrysosperma (Persoon: Fries) Fries, distin-
val galleries. guished by characteristic orange conidial
Feeding bioassays. We observed feed- tendrils (Callan 1998).
ing on both the petioles and leaves as did
1
J.Entomol. Soc. Brit. Columbia 102, December2005 31
Table 1.
Comparison ofbehavioural activity by male and female S. calcarata within perforated centres
ofarena floor above treatment (i.e. trembling aspen leaves) and controljars in the still-air ol-
factometer.
Observations Females Males
Observations ofbeetles within arena circle circumscribingperforated
area above treatment orcontrol stimulus, 30 sec intervals for2 h.
no. replicates 7 7
meanno. observations± SE
treatment stimulus 55.4±18.5 41.9±8.8
control stimulus 26.3 ± 10.8 41.9± 18.5
t-value 1.99 0.00
Probability^ 0.047 0.50
Observations offeeding onperforatedarea ofarena floorabove
treatment orcontrol stimulus
no. replicates 8 1
no. times most feeding above treatment stimulus 7^ 6
no. times most feeding above control stimulus 0 0
no. timesno feeding damage observed 1 5
Chi-square value 7.00 6.00
Probability 0.008 0.01
' In one trial feeding damage was observed above both stimuli, but damage was much greater
overthe treatment stimulus.
DISCUSSION
Ourresults indicate that S. calcarata can requiring little movement by feeding bee-
locate potential hosts by olfaction, can dis- tles. Similarly, in an unpublished study con-
criminate among tree species through gusta- ducted by C.L. Broberg and R. Gries
tory cues, and may reject trees for oviposi- (SFU), 15 antennally-active volatiles from
tion iftheirdiameter is too small. the bark oftrembling aspen were identified
Females were attracted to the volatiles by coupled gas chromatographic electro-
from leaf-bearing twigs oftrembling aspen antennographic detection analysis. How-
in an arena olfactometer (Table 1). The fact ever, in six field-trapping experiments, no
that males chewed the paper above treat- S. calcarata were captured to various par-
ment but not control stimuli suggests they tial or complete blends ofthese compounds.
too are attracted to host volatiles. In the These results may indicate that S. calcarata
field experiment, we had hypothesized that use leafvolatiles in orientation toward suit-
S. calcarata brood trees would produce able hosts during flight.
ethanol, and possibly other metabolites The lack of a strong olfactory response
caused by wounding, and that the combina- by S. calcarata is not surprising. As a spe-
tion would be attractive. The positive re- cialist of weakened hosts that may support
sponse to leafy twigs, and the failure to multiple generations on the same tree
induce significant attack on trees that were (Hanks 1999), S. calcarata is not likely
wounded, ethanol-baited, or both, suggests subject to strong selection pressure to adapt
that initial orientation is to volatiles from to finding new hosts. Furthermore, Popidus
leaves on which adults feed. Oviposition spp. are pioneer species and often occur in
tends to be located in the upper parts ofthe locally abundant populations. Thus emer-
bole beneath the canopy (Peterson 1947), gent S. calcarata may not need to disperse
32 J. Entomol. Soc. Brit.Columbia 102,December2005
CHOICE EXPERIMENT
Females Males
UJ
CO
3
+
E
o
E
0
3
TA CW Wil TA CW Wil
(C/)
o
o
NO-CHOICE EXPERIMENT
CO
£ 8 5
CO Females Males
^CO 1
6
c 1
CO 1
0
TA CW Wil TA CW Wil
Host species
Figure 2. Leafarea consumed by female and male S. calcaratawhenpresentedwith the three
potential hosts simultaneously (choice experiment) or separately (no-choice experiment). Bars
within an experiment and sex with the same letter are not significantly different, REGWQ test,
P< 0.05. TA=tremblingaspen, CW =blackcottonwood, Wil= Scouler's willow.
long distances to fmd a suitable host. In posit on these newly found hosts, they en-
contrast, stressed hosts which are moribund gage in maturation feeding on healthy trees
and can only support one generation ofbee- (Hanks 1999). Weakened host specialists
tle (Hanks 1999) are often rare and/or like S. calcarata can use a single individual
patchy in distribution. Cerambycid special- for all functions; thus even the malformed
ists on these hosts have evolved strong emergent adults incapable of flight ob-
long-distance response mechanisms that served by us and others (Peterson 1947;
often involve orientation to host volatiles Drouin & Wong 1975), can experience re-
from recently downed or injured trees, productive success without long range dis-
smoke volatiles from burned trees, or persal and olfactory orientation to suitable
pheromones produced by secondary bark hosts.
beetles pheromones (Allison et al. 2004). Both sexes clearly preferred trembling
Ahhough these cerambycids mate and ovi- aspen in choice feeding bioassays and re-
J.Entomol. Soc.Brit.Columbia 102,December2005 33
Table 2.
Comparison ofoviposition by S. calcarata on bolts from three different hosts whenboh diame-
ters were unequal or similar.
Experimental Bolt diameter (cm) Mean no.
Species
description Range Mean ± SE^ ovipositions ± SE
Bolt diameters unequal Trembling aspen 6.3- 13.2 9.5 ±0.8 a 21.0±9.6b
(2002) BXdiok Cottonwood 8.9- 16.7 12.2 ±0.9 a 27.5 ± 9.4 a
Scouler's willow 3.2-5.5 4.6 ± 0.3 b 0.4 ±0.2 c
Bolt diameters similar Trembling aspen 7.8- 17.1 13.5 ±0.6 a 4.4 ±2.1 a
(2003) Black cottonwood 8.1 - 17.3 13.1 ±0.6 a 8.0±3.2 a
Scouler's willow 9.2- 17.0 12.6 ±0.6 a 8.3 ±2.8 a
'Means within an experiment and column followed by the same letter are not significantly
different, REGWQ test, P < 0.05. ANOVA statistics as follows: 2002 bolt diameter F2.18 =
33.83, P < 0.0001 oviposition F2.18 = 21.17, P < 0.0001; 2003 bolt diameter F2.24 = 2.57, P =
;
0.10; oviposition F2.24= 1.17,P= 0.33.
jected other species, but in the no-choice The lack of discrimination between
bioassays, females did not discriminate hosts for oviposition when trembling aspen
between trembling aspen and black cotton- leaves were available for maturation feed-
wood, and males accepted black cotton- ing, and diameters of bolts from the three
wood more than Scouler's willow (Figure species were equalized, indicates that host
2). Females may have higher nutritive re- volume is more important than species for
quirements than males and therefore cannot larval feeding and development (Table 2).
afford to be as selective. Preference for Oviposition in large-diameter hosts would
trembling aspen could be a resuh of local be adaptive in ensuring that most hosts did
adaptation to a species that comprises 4.6 not suffer breakage during the three to four
times more wood volume in BC than black years requiredforlarval development.
cottonwood (BC Ministry ofForests 1998). In conclusion, lack ofevidence for long-
Saperda calcarata is mobile enough to range olfactory orientation to new hosts,
sample numerous trees before finding one correlation between S. calcarata incidence
that is suitable forfeeding. in BC and gustatory preferences, high mo-
There are few records in BC ofS. cal- bility, and lack of discrimination between
carata attack on Salix spp. In Saskatche- hosts for oviposition, suggest that feeding
wan, however, both Salix and Populus spp. preference constitutes the predominant
were reported to be "readily eaten" by mechanism ofhost selectionbyS. calcarata
adults (Peterson 1947). Thus, there couldbe in BC.
host-related ecotypes in different regions of
NorthAmerica.
ACKNOWLEDGEMENTS
We thank Nicole Vander Wal, Ashley Ltd., Louisiana-Pacific Canada Ltd., Man-
Mohle, and James Inkster for assistance; ning Diversified Forest Products Ltd., Mil-
and Leland Humble for review of this lar-Western Forest Products Ltd., Phero
manuscript. The research was supported by Tech Inc., Scott Paper Ltd., Slocan Forest
Abitibi Consolidated Inc., Ainsworth Lum- Products Ltd., Tembec Forest Industries
ber Co. Ltd., B.C. Hydro and Power Au- Ltd., TimberWest Forest Ltd., Tolko Indus-
thority, Bugbusters Pest Management Inc., tries Ltd., West Eraser Mills Ltd., Western
Canadian Forest Products Ltd., Gorman Forest Products Ltd., and Weyerhaeuser
Bros. Ltd., International Forest Products Canada Ltd.
34 J. Entomol. Soc. Brit. Columbia 102, December2005
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