Variation in attack by Sitka spruce weevil, Pissodes strohi (Peck), within a resistant provenance of Sitka spruce

7 Pages·1993·3.8 MB·English

by  Rene I Alfaro

24 J.Entomol.Soc.Brit.Columbia90,December,1993
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Zar,J.H. 1984.Biostatisticalanalysis.Prentice-Hall,EnglewoodCliffs,N.J.
Variation in attack by Sitka spruce weevil,Pissodes strobi
(Peck), within a resistant provenance ofSitka spruce
RENE ALFAROand M. HULME
I.
FORESTRYCANADA,PACIFICFORESTRYCENTRE,506WESTBURNSIDEROAD,VICTORIA,BC,
CANADAV8Z1M5
C.YING
BRITISHCOLUMBIAMINISTRYOFFORESTS,RESEARCHBRANCH,BASTIONSQUARE,
VICTORIA,BC,CANADA V8W3E7
ABSTRACT
Variation intreeheightandnumbersofattacksbytheSitkaspruceweevil(=whitepinewee-
vil),Pissodes strobi (Peck), were studied among families ofaresistantprovenance ofPicea
sitchensis(Bong.)Carr.attwoVancouverIslandsites.AtSayward,after 14years,thenumber
oftreesattackedvariedbyfamilyfrom0to80%.Asignificantassociationwasfoundbetween
thepercentageoftreesattackedinafamilyandthemeanheightofthefamily.Tallfamilieswere
generallyattackedmore. AtFairHarbour(aclonaltest),only 12%ofthetreesfromtheresis-
tantprovenancehavebeen attackedaftersevenyears, with allbutoneoftheattacksconcen-
tratedononeofthetwofamiliestested.Amultigenicormulticomponentbasisforresistanceis
proposedanddiscussed.
INTRODUCTION
TheSitkaspruceweevil(=whitepineweevil),Pissodesstrobi(Peck),isamajorcauseoffail-
ureinreforestationprogramswithSitkaspruce,Piceasitchensis(Bong.)Carr.,incoastalBritish
Columbia(B.C.),Washington,andOregon(FumissandCarolin 1977).Theadultsemergefrom
overwinteringinearly spring,andmovetothe 1-yearoldterminalshoot(leader)wherethefe-
maleslayeggsunderthebarknearthetip. Iftheweevillarvaebecomeestablished,theymove
downwards,miningandconsumingthephloemandeventuallykillingtheleader(Silver 1968).
Intheliterature,thesuccessfulcolonizationanddestructionofthetreeleaderbyP.strobiisgen-
erally called a weevil attack; this terminology is also used here. Repeated leaderdestruction
causes height-growth loss and stem deformities whichreduce the tree's value (Alfaro 1989a,
1992). Althoughthetree survives the attack, stuntedtrees areoften suppressedbycompeting
vegetation(Alfaro 1982).Otherimportanttreespeciesdamagedbythisinsectareeastemwhite
pine,PinusstrobusL.,ineastemNorthAmerica(MacAloney 1930),Engelmannspruce,Picea
engelmanniiParry,andwhite spruce,Piceaglauca (Moench)Voss., incentralBritishColum-
biaandtheprairieprovinces (Stevenson 1967).
AnalysisofseveraltrialsinBritishColumbiaprovidedstrongevidenceofgeneticvariation
J.Entomol.Soc.Brit.Columbia90,December, 1993 25
inthesusceptibilityofSitkasprucetoweevildamage(Ying 1991,AlfaroandYing 1990).Ge-
neticresistancetoweevilattackwasalsodemonstratedforinteriorsprucebyKissandYanchuk
(1991).Theseanalysesindicatethatsomeprovenancesandfamiliesshowresistanceintheform
ofreducednumbersofweevil attacks. This wasthecase in Sitkaspruce treesfromtheHaney
provenanceintrialsatSaywardandFairHarbour,whichgrewwellandweretheleastdamaged
(Ying 1991,AlfaroandYing 1990).Mechanismsofresistancearecurrentlyunderinvestigation;
onebasedonsupemumeraryresincanalshasbeenproposed(E.TomlinandJ.H. Borden,per-
sonalcommunication,SimonFraserUniversity).
Ying (1991) noted that resistant provenances ofSitka spruce originate from areas ofhigh
weevilhazard, suchas HaneyorSquamishontheB.C. mainland. Hehypothesizedthatherbi-
voreselectionmayhavefavoredaresistantgenepoolintheseareassothatsurvivorshavehigh
levelsofresistance.AlfaroandYing(1990)identifiedtheSkeenaRiverareaofB.C.asanother
areawherehigherfrequencyofresistantindividualscouldbefound. Inthisarea,extensivehy-
bridizationofSitkawithwhitespruceoccurs.VariationinsusceptibilityamongdifferentPicea
speciesandtheirhybridshasbeenreported(Mitchelletal. 1990).
Alfaro and Ying (1990) also demonstrated variation in the ability oftrees to recoverfrom
weevildamage, since the type ofdefectformedafterattackvariedbyprovenance andfamily.
Someprovenanceshadabove-averagenumbersofattackspertreebutstillwereabletodevelop
into merchantable trees. An example oftolerance to weevil damage was the Big Qualicum
provenance,whichwasamongthetallestattheSaywardtrialeventhoughitsustainedrepeated
attacks.
The objectives ofthis paperwere to examine the rates ofrepeated attacks among families,
treesandclonesofthemostresistantprovenancefoundtodateinB.C.(theHaneyprovenance),
andtodescribe someofthefactorsthatdeterminedattacks on individuals ofthisprovenance.
In particular, we tested whetherthe demonstratedpreference ofthe weevil forthe tallest and
fastestgrowingtreesinaplantation (Mitchelletal. 1990, Alfaro 1989b,Garaetal. 1971, Sil-
ver 1968) alsoholds true withintheHaneyprovenance. Forthis study, weuseddatacollected
atSaywardandFairHarbourin 1988, 1991 and 1992.
MATERIALS AND METHODS
TheSaywardprovenancetestwasestablishedinthespringof1974intheSalmonValley,near
Sayward,B.C.,withthepurposeofcomparinggrowthandsurvivalofacollectionofopen-pol-
linationfamiliesfromseveral B.C. provenances. Theplantationwas firstattackedbyP. strobi
when the trees were 5 years old. The site was assessed in the fall of 1988; forevery tree we
recorded: totalheight,diameteratbreastheight(DBH), andthenumberoftimesthetreeshad
sustainedweevilattack.Weevilattackswererecognizedbecause,inmostcases,remainsofthe
destroyedleaderwerepresentandpupalchamberswereevident.Theplantationoriginallycon-
sistedoftwo blocks, A andB, butonly Block B was assessedbecause Block A had suffered
flooddamage.BlockBconsistedof141 rowsoccupying2.8ha,andcontained4389livingtrees
from34provenances.Eachprovenanceconsistedofavariablenumberofwind-pollinatedfam-
ilies. TheresistantHaneyprovenance, which was theobjectofthis study, was representedby
81 trees from 8 families. Furtherdetails on this plantation and on the geographic location of
provenancesourcescanbefoundinAlfaroandYing(1990).
The 1988recordsfortheSaywardplantation(BlockB)wereassessedtodeterminethenum-
berofpastattacksandtheheightoftreesintheHaneyprovenance.Becauseoflimitationsofthe
experimentaldesignofthistestnoattemptwasmadetoanalyzethecomponentsofthevariance
ortocalculateothergeneticparameters. Instead,wereliedonnon-parametrictestsofvariance
andassociation.TheKruskal-Wallistest(SokalandRohlf1969)wasusedtotestforfamilyvari-
ationinmeannumberofattackspertree.TheSpearmanrankcorrelationcoefficient(Sokaland
Rohlf1969)wasusedtotestforasignificantassociationbetweenpercentageoftreesattacked
in afamily and meanfamily height. The same procedure was usedto test forassociation be-
tweenthemeannumberofattackspertreeinafamilyandmeanfamilyheight.
TheFairHarbourplantationisaclonaltrial(grafting)establishedin 1984totesttherepeata-
bilityofprovenanceresistancetoweevilattackobservedinprovenancetests(Ying 1991).The
26 J.Entomol.Soc.Brtt.Columbia90,December,1993
donorparents(ortets)originatedfromtreesineightprovenancestestedattheSaywardsite,plus
twotreesfromtheGreenTimbersplantationwhichshowedhighresistancetoweevilattack(Al-
faro 1982).EighttreesfromtheresistantHaneyprovenance(fourtreeseachfromfamily0and
1)wereincludedinthetest.Thelayoutofthetestconsistedof16blocksinwhichatotalof640
graftsweretested; eachortetwasrepresentedby 16grafts(ramets),onerametineachblock.
TheattacksontherametsatFairHarbourwerecountedinOctober 1991 andontheortetsat
SaywardinOctober 1992.
Todetermineifattacksontreesoccurredindependentlyofeachotherorifthepresenceofone
attackenhancedtheprobabilityofasubsequentattackonthe sametree,thedistributionofthe
attackspertree atboth sites was comparedto thatexpectedfrom aPoissondistribution. Data
collectedin 1988wereusedfortheanalysisoftheSaywardsiteand 1991 datafortheFairHar-
boursite. However,becauseofthelowattackratesatFairHarbour,aChi-square-testofgood-
ness-of-fit(SokalandRohlf1969)wasdoneonlyfortheSaywarddata.
Table1
Meantreeheight,numberofSitkaspruceweevilattackspertreeandpercentoftreesattackedamongtrees
oftheresistantSitkaspruceHaneyprovenance(standarddeviationinbrackets).Datacollectedin 1988at
Saywardandin 1991 atFairHarbour.
MeanNo.
Locationand Number MeanHt attacks %trees
familyNo. oftrees (m) pertree attacked
Sayward
0 6 6.6(1.6) 0.3 (0.5) 33
1* 5
3 30 6.0(1.2) 1.1 (1.1) 60
4 22 5.3(1.9) 0.5 (0.7) 32
5 4 4.0(1.0) 0.0 (0.0) 0
8 7 4.2(0.6) 0.9 (1.6) 29
12 7 5.1 (0.6) 0.4 (0.8) 29
13 5 6.0(1.0) 1.8 (1.1) 80
FairHarbour
0 62 4.6(0.9) 0.03 (0.25) 2
1 63 4.7(0.9) 0.25 (0.54) 22
*ThisfamilywaspresentonlyatSaywardBlockA,whichwasnotassessedin 1988.Anassessmentin
1992indicatedthat60%ofthetreesinthisfamilyhadbeenattackedatleastonce.
Table2
FrequencydistributionofSitkaspruceweevilattackspertreeamongtreesfromtheresistantSitkaspruce
Haneyprovenance.TheexpectedfrequenciesfromaPoissondistributionaregiveninbrackets.Datacol-
lectedin 1988atSaywardandin 1991 atFairHarbour.
Attacks Sayward FairHarbour
pertree No.trees' No.trees'
0 46(36) 111 (109)
1 14(29) 10 (15)
2 15(12) 4 (1)
3 5 (3)
4 1 (1)
1. FortheSaywardsite,aChi-square-testdetectedasignificantdepartureofthenumberofattackspertree
frompredictedPoissonfrequencies(P<0.01).Becauseofthesmallnumberofattacks,andlowcellfre-
quencies,nostatisticaltestsweredoneontheFairHarbourdata.
.
J.Entomol.Soc.Brit.Columbia90,December, 1993 27
RESULTS
SaywardTest
The 1988 attackrecords indicatedthatonly43% oftreesfrom theHaneyprovenance were
attackedoneormoretimes, whereas76% ofthetreesintheentireSaywardBlockB hadbeen
attacked.ThepercentageoftreesattackedamongfamilieswithintheHaneyprovenancevaried
significantly(Chi-squaretest,P<0.05)byfamilyfrom0%(Family5)to80%(Family 13)(Table
1).ThemeannumberofattackspertreefortheHaneyprovenancewas0.8 (rangingfrom0to
4)whichwasabouthalfofthemeannumberofattackspertreerecordedfortheentireBlockat
1.5 (range0to7, AlfaroandYing 1990). The mean numberofattacks pertree varied signifi-
cantlyamongtheHaneyfamiliesfrom0(Family5)to 1.8(Family 13)(Table 1)(Kruskal-Wal-
lisTest,P<0.05).
The distribution ofthe number ofattacks per tree departed significantly (Chi-square test,
P<0.01)fromthevaluesexpectedfromthePoissondistribution,indicatingaclumpeddistribu-
tion.Therewerehighernumbersoftreesthatremainedundamagedandhighernumbershaving
repeatedattacks thanexpectedifthe attacksoccurredatrandom (Table 2). This allowedus to
concludethatthepresenceofoneattackonatreeenhancedthechancesofatreebeingattacked
again. AlfaroandYing (1990) arrivedatthe sameconclusion when theyexamined the attack
distributionfortheentireSaywardBlockBplantation.
m m
In 1988,theHaneyprovenancetreesaveraged5.5 inheight,almost2 tallerthantheav-
erageheightfortheentiresite(3.6m). However,therewasconsiderablevariationinheightby
family(range4.0to6.6m).The Spearmanrankcorrelationtestdetectedasignificantassocia-
tionbetweenthepercentageoftreesattackedinafamilyandthemeanheightofthefamily (rs
=0.88,P=0.01)(Fig. 1).Becauseofthenegativeeffectofweevildamageonheightgrowth,this
correlationisonlyameasureofassociation,ratherthanacause-effectrelationship. Nosignifi-
cantcorrelationwasfoundbetweenthenumberoftimesanindividualtreewasattackedandtree
height.
FairHarbourTest
Overall, 12%ofthetreesfromtheHaneyprovenanceattheFairHarboursitewereattacked
(14treesupto 1991).Thisismuchlowerthanthe69%foundfortheentire site. AsattheSay-
wardsite,moretreeshadrepeatedattacksthanpredictedbythePoissondistribution(Table2).
There werefourtreesattackedtwice; ifattacksoccurredatrandom, only onetree wouldhave
beensoattacked(Table2).However,becauseatthissiteweevildamageisstilllightandthisre-
sultedinlowcellfrequencies,aChi-squaretestwasnotdone.Allbutoneoftheattacksoccurred
among trees ofFamily 1, resulting in attack rates of2% for Family 0 and 21% forFamily 1
(Table3).MeanheightoftheHaneyrametsvariedfrom4.0to5.2m.Nocorrelationwasfound
betweenthepercentageoftreesattackedinacloneandmeanclonalheight(Spearmanrankcor-
relationtestnotsignificant).
A
comparisonoftheattackratesontheFairHarbourrametswithattackratesontherespec-
tiveortetsatSaywardindicatedaverygoodcorrespondence(Table3).Therewasaverylowat-
tackrateonbothortetsandrametsfromFamily0,withonlyonetreebeingattackedateachsite.
BothortetsandrametsfromFamily 1 hadsustainedhigherattackratesthanFamily0,withthree
ofthefourortets atSaywardand 13 of63 ramets atFairHarbourbeing attacked (Table 3). In
bothfamiliestherewasoneortetattackedatSaywardbutnoattackamongtherespectiveFair
Harbourramets. There werealsoattacks amongramets fromortets whichremainedfreefrom
attackatSayward,e.g.treeNo. 6fromFamily 1
DISCUSSION
ThelowattackrateoftheHaneyprovenanceattheSaywardandFairHarboursitesconfirms
the existence ofresistance to weevil attack in this provenance (Ying 1991, Alfaro and Ying
1990).This studyalsosuggeststhatindividualtreesandfamiliesfromthesameHaneyprove-
nancedifferindegreeofresistance.
ThelargenumberoftreesoftheHaneyprovenancethatremainedfreefromweevilattackat
bothsitesisprobablynotduesolelytogeneticresistance. Onefactorinfluencingtheprobabil-
,
28 J.Entomol.Soc.Brit.Columbia90,December,1993
Table3
AttacksbytheSitkaspruceweevilontwoSitkasprucefamiliesplantedattheSaywardsiteandclonedat
theFairHarboursite.Datacollectedin 1992atSaywardandin 1991 atFairHarbour
Plantation
SaywardOrtets FairHarbourRamets
Attacks Grafts Grafts Attacks*
FamilyNo. TreeNo. Trees pertree alive attacked pergraft
0 2 0 16 0 0
5 0 14 0 0
6 0 16 1 2
7 1 15 0 0
1 1 1 15 0 0
2 2 16 3 1
2 14 8 1.4
6 0 15 2 1
*Meannumberofattacksonattackedgrafts.
ityofattackonatreeis itsrateofgrowth. SeveralreportsindicatethattheSitkaspruceweevil
prefersthefastest-growingtreesinastand(Mitchelletal. 1990,Alfaro 1989b,Garaetal. 1971
Silver 1968). AlfaroandYing (1990)foundthat,atthe Saywardsite,treesgrowinginpatches
ofsevereattackwere significantlytaller(3.8 m) thantreesgrowinginareasoflowattack(3.5
m). Thispreference wasalsoevidentinthis study amongthetreesoftheresistantprovenance
(Fig. 1). TheonlyHaneyfamilyatSaywardwhichwasfreefrom weevilattackwasFamily5,
whichwasalsotheshortest.
ThepreferenceofP.stwbiforthefastest-growingfamilies(evenamongtheresistantprove-
nance)isdifferentfromthefindingsofKissandYanchuk(1991)whofoundtheoppositeamong
families ofwhite spruce attackedbythe same insect. Apossibleexplanationforthis apparent
contradiction is thatP. stwbimay seektomaximizethe amountoflarvalfoodduringhostse-
lection.P. stwbilarvaeconsumetheleaderphloem,therefore,leaderswiththickerphloemare
probablymoreattractivethanleaderswiththinphloem. InSitkaspruce,thickphloemiscorre-
lated with long leaders (Alfaro, unpublished data). It is possible that, because ofthe different
growth characteristics ofwhite spruce (much slowergrowth than Sitka spruce) thickphloem
maybenegatively correlated with leaderlength in this species. Therefore, anegativecorrela-
tionbetweenattackrateandrateofgrowthwouldresult. However,furtherresearchisrequired
toproveordisprovethishypothesis.
Thespatialdistributionofweevilattacksinaplantationishighlyclumped(AlfaroandYing
1990,Graham 1951).This studydemonstratedthat, atbothtestsites,attacksontreesfromthe
resistantprovenancewerealsoaggregatedandthat, oncetreeswereattacked,theirchancesof
furtherattackincreased.Thisdistributionprobablyresultsfromthelowdispersalabilityofthe
weevilandfromthetendencyoftheweevilstooverwinterneartheattackedtree.Moreover,the
formationofmultipleleadersonattackedtreesincreasestheprobabilityoffurtherattack.This
aggregationintheweevilpopulationmustbeconsideredwhenselectingforresistance. Asus-
ceptible treemay appearresistantandbeundamagedifithappenedtooccurinanareaoflow
weevildensity.Therefore,selectionforresistanttreesshouldbedoneinareasoftheplantation
ofhighweevildensity.
ThelowoverallattackratesamongtheHaneytreesattheFan-Harboursiteascomparedwith
theSaywardsite(Table2)couldresultfromseveralfactorswhicharedifferentbetweenthetwo
plantations. The Fair Harbour test was initiated 10 yr after the Sayward test, therefore trees
have had a shorterexposure to the weevil. The Fair Harbour trees were clones produced by
grafting,andthuscoulddifferfromthewind-pollinationtreesatSaywardduetoaninfluenceof
MeanFamilyHeight(m)
Figure 1. Relationshipbetween the percentage ofSitka spruce trees in a family attacked by the Sitka
spruceweevilatSaywardandmeanfamilyheight. Allfamilies(indicatedbynumbers)arefromthere-
sistantHaneyprovenance.Datacollectedin 1988.
therootstockonthephysiologyofthetree. However,therankingofresistanceamongthetwo
families wasthesameatbothsites: Family0wasmoreresistantthanFamily 1 (Table3). This
indicatedthatselectionforresistanceatanearlyage(9yearsatSayward)maybereliable.
Thelargevariationinthepercentageoftrees attackedamongthe wind-pollinationfamilies
ofthe Haney provenance, as well as the existence ofa gradation in resistance with several
provenances showingintermediateresistance,e.g. Squamish (AlfaroandYing 1990), suggest
aresistancemechanismthathasamulti-allelicormultigenicbasisortotheexistenceofseveral
resistance mechanisms which accumulate andperhaps synergize in differenttrees. Future re-
searchshouldconcentrateontheelucidationoftheresistancemechanismsandonunderstand-
ingtheirgeneticbasis. Ying (1991) notedthedesirability ofdeveloping varieties which com-
bine different resistance mechanisms and thus run a lower risk ofinducing the evolution of
weevilpopulationswhichcanovercometreeresistance. Howeverconfirmationofthishypoth-
esisrequu-estheestablishmentandevaluationofprogenytests.
Ultimately, itis likelythatthedegreeofattackbyP. strobion aSitkasprucetree,family,or
provenanceisduetoacombinationoffactors: resistancefactorsandgrowthcharacteristicsof
the trees which are subject to both genetic and environmental influences, plus an element of
chance.Someofthesefactorscouldbemanipulated,alongwithsilviculturaltreatmentssuchas
shading(McLean 1989)orspacing(AlfaroandOmule 1990),inanintegratedpestmanagement
programforcontrolofthisdestructiveinsect.
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106.Victoria,B.C.,Canada. 17pp.
Life history and pheromone response in Pissodes schwarzi
Hopk. (Coleoptera: Curculionidae)
LORRAINEE. MACLAUCHLAN,JOHN H. BORDEN^
andlNGRIDPRICE^
B.C.FORESTSERVICE,KAMLOOPSFORESTREGION,515COLUMBIASTREET,
KAMLOOPS,B.C.V2C2T7
ABSTRACT
PitfalltrapsbaitedwithlivePissodesschwarziHopk.malespluspinesectionscaptured46fe-
maleP.schwarzifrom 1Juneto1 September, 1989,indicatingthepresenceofamale-produced
sexpheromone. Noweevils werecapturedinunbailedtraps, orthosebaitedwithfemaleson
pineorpinesectionsalone. SeasonalresponseofP.schwarzifemalestothemale-baitedpifall
traps indicated peak periods ofactivity in early June, representing overwintered adults, and
mid- to late July, corresponding to the emergence ofnew adults. Development time ofP.
schwarzivarieddependingonovipositionlocationonthetree.Overwinteredbroodadultsbe-
gantoovipositinMayandcontinuedthroughAugust.
INTRODUCTION
TheYosemitebarkweevil,PissodesschwarziHopk.,attacksandbreedsinthebole,rootcol-
larandlargerootsofstressedordyingtrees (Wood 1964; Stevens 1966). Hopkins (1911) and