Published by Utah State University Extension and Utah Plant Pest Diagnostic Laboratory July 2012 ENT-165-12 Bark Beetles Ryan S. Davis, Arthropod Diagnostician, and Darren McAvoy, Extension Forestry Associate WHAT YOU SHOULD KNOW • Bark beetles are a significant cause of tree mortality in the forest and urban environment. • To protect high-value trees around homesites, use preventative trunk sprays of carbaryl, permethrin, and bifenthrin prior to beetle flight. • Soil- and trunk-applied systemic insecticides (e.g., imidacloprid and dinotefuran) do not sufficiently protect trees from bark beetle attack. Fig. 2. Typical top-down dieback pattern on pines infested by Ips beetles 2 . Bark beetles are one of the most destructive forest pests in the world. They are different than the larger longhorned and roundheaded/metallic woodboring beetles commonly infesting the inner wood of trees. The largest bark beetle, the red turpentine beetle (Dendroctonus valens), reaches only 8.3 mm in length. Because of their tiny size (Fig. 1), bark beetles are not effective tree killers as individuals. Instead, primary bark beetles work together, sending pioneer beetles to search for stressed or dying trees. When pioneer beetles find a weakened tree, they bore into and feed BIOLOGY on the thin phloem layer just under the bark. As they feed, chemicals from their food are converted into attractive chemicals, signaling to other beetles of the same species that a suitable host was found. Beetles that detect the airborne chemicals will fly to the stressed tree, bore into the phloem, create a mating (nuptual) chamber, mate, and hollow-out a parental gallery laying eggs as they progress. Usually, many beetles attack the same tree in a short period of time allowing them to overcome its defenses (e.g., resin in pines). This is called mass attack. After egg hatch, immature beetles (larvae) (Fig. 12) begin feeding outward from the parental gallery, girdling the tree. This larval girdling is the same as killing a tree by deeply scoring its entire circumference with a knife or Fig. 1. Average size of an adult bark beetle compared to a penny 1 .
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Published by Utah State University Extension and Utah Plant Pest Diagnostic Laboratory July 2012ENT-165-12
Bark BeetlesRyan S. Davis, Arthropod Diagnostician, and Darren McAvoy, Extension Forestry Associate
WHAT YOU SHOULD KNOW• Barkbeetlesareasignificantcauseof
• Soil-andtrunk-appliedsystemicinsecticides (e.g., imidacloprid and dinotefuran)donotsufficientlyprotecttreesfrombarkbeetleattack.
Fig. 2. Typical top-down dieback pattern on pines infestedbyIpsbeetles2.
Barkbeetlesareoneofthemostdestructiveforestpestsintheworld.Theyaredifferentthanthelargerlonghornedandroundheaded/metallicwoodboringbeetlescommonlyinfestingtheinnerwoodoftrees.Thelargestbarkbeetle,theredturpentinebeetle (Dendroctonus valens),reachesonly8.3mminlength.Becauseoftheirtinysize(Fig.1),barkbeetlesarenoteffectivetreekillersasindividuals.Instead,primarybarkbeetlesworktogether,sendingpioneerbeetlestosearchforstressed or dying trees. When pioneer beetles findaweakenedtree,theyboreintoandfeed
BIOLOGY
onthethinphloemlayerjustunderthebark.Astheyfeed,chemicalsfromtheirfoodareconverted into attractive chemicals, signaling tootherbeetlesofthesamespeciesthatasuitablehostwasfound. Beetles that detect the airborne chemicalswillflytothestressedtree,boreintothephloem,createamating(nuptual)chamber,mate,andhollow-outaparentalgallerylayingeggsastheyprogress.Usually,many beetles attack the same tree in a short periodoftimeallowingthemtoovercomeitsdefenses(e.g.,resininpines).Thisiscalledmassattack.Afteregghatch,immaturebeetles(larvae)(Fig.12)beginfeedingoutwardfromthe parental gallery, girdling the tree. This larval girdling is the same as killing a tree by deeply scoringitsentirecircumferencewithaknifeorFig.1.Averagesizeofanadultbarkbeetlecompared
to a penny1.
HOW DO I KNOW IF MY TREES ARE INFESTED?
Fadingtreecrowns(Figs.3-4)aregoodindicatorsofbarkbeetleinfestationorotherhealthproblems.Insomecases,crownfadingcanbedelayedbycoldtemperatures.Treesattackedinfallmayremainmostlygreenuntilearlysummer.Crownfadingrangesfromveryslightoff-green,toyellow,brown,andred, depending on how recently the tree was attacked. Trees attacked by Ips beetles usuallyhavecrowndie-backfromthetopdown,whichmayhappenoverthecourseofaseasonorafewyearsassuccessivebeetlegenerations attack progressively lower portions ofthetree. Ifthecrownappearsoffcolored,completeathoroughinspectionofthetreetrunkandbranches.Lookforasawdustlikesubstance(frass)thatcanbefoundinthecracksandcrevicesoftreebarkoronthegroundaroundthetrunk(Fig.5).Alsolookforpitchtubes(Figs.6-8),whichareresindepositsexudedfromtreesinanattempttodefenditself.Pitchtubesaremostcommononpinetrees,butsmallamountsofpitchfromsomehardwoods may also be seen. The presence ofpitchtubesand/orfrassindicatestheneedforfurtherinvestigation.Ifthetubesand/orfrassarevisibleonmorethanhalfofthetrunkcircumference,useahatchettopullbackbarkfromanareaunderthepitchtubesandexaminetheexposedwoodandbackofbark. Lookforsignsofcurrentorpastbeetleinfestationssuchasgalleries(Fig.10),eggs,larvae(Fig.12),pupae,andadultbeetles.Ifgalleries and larvae are present, this indicates acurrentattack.Ifthegalleriesareemptyandnolarvae,pupaeoradultbeetlesarepresent,thentheinfestationislikelyold.Notethatsomebeetles,suchasthewesternpinebeetle,will
saw.Oncethephloemlayerisgirdled,nutrienttransport within the tree stops, and the tree eventuallydies.Manybarkbeetlescarryafungusthatinhibitswatertransportwithinthetree, aiding in tree death. Inanurbansetting,treesareeasilystressedbyheatanddrought,soilcompaction,over/underwatering,oldage,and mechanical damage making them prime targetsforbarkbeetles.Ourhabitofplantingidenticaltreespeciesingroupsorrowsmakesthe problem worse, allowing beetles to easily move between closely growing host trees and causemajoraestheticdamage.
BEETLE IDENTIFICATION AND COMMON UTAH BARK BEETLES
Bark beetles are small and similar looking.Alwayshaveyourbeetleidentifiedbyaprofessionalentomologist.However,homeowners can narrow down the possibilities byansweringthefollowingquestions:
3)Whatisthegeneralappearanceofthebeetle?Lookattheadultbeetlepicturesbelowandmatchmajorfeatures.Beetlesareextractedfromthetreeusingdestructivehatchet sampling methods as well.
entertheouterbarklayersinlaterlarvalstages.Iftheconditionofthephloemlayer(soft,white,thinlayerbetweenthebarkandwoodlayers)isbrowntoblack,orcompletelydried-up,thenthetreemaybedead.Checktherestofthecircumferenceofthetreeforlivephloem.Ifnolivingphloemisfound,thetreeshouldberemoved and treated to kill the beetles; see the“Sanitation”sectionfortechniques. Beetleexitholesoftenhavea“shotgun”patternintreebark(Figs.9&11),indicatingthat bark beetles have already exited the tree. Ifyouseeanysignsofbarkbeetles--fadingcrown,pitchtubes,frass,galleries(Fig.10),larvae(Fig.12),oradults--besuretoexaminetherestofthetreesonyourpropertyforsignsofbeetleattack,especiallytreesofthesameorrelatedspecies.Ifyouliveclosetoyourneighbors,theyshouldalsobenotifiedtoexaminetheirtrees.Ifyouarenotcomfortableevaluatingyourowntree,contactaqualifiedarboristforhelp,orsubmitsamplestotheUPPDL.
Ipsbeetlesarethemostcommonlyencounteredbarkbeetlesinlandscapepines.Adultbeetles(topleftandright)havespinesalongtheirouterwings.Ipsgalleriesresembletheshapeofanoctopusbutwithfewerarms.Thereisacenterchambergivingrisetomultipleparentalgallerieswhereeggsarelaid.Uponhatching,larvaeradiateoutwardfromtheparentalgallery.Larvalgalleriesbecome progressively wider as the larvae grow, terminating in acirculartoovalpupalchamber.Ideally,adultsandimmaturebeetleswillbepresentinyoursample,indicatingtheyarestillinthetree.Ifemptygalleriesandpupalchambersarepresentthenit is likely the beetles have emerged to attack another host.
BarkbeetlesinthegenusDendroctonusaresomeofthemostdevastatingforestinsectpestsintheworld.Themostnotablespeciesinthewestisthemountainpinebeetle(MPB),responsibleforthedestructionofmillionsofacresoftimbereveryyear.Mountainpinebeetlelessfrequentlyattackspinetreesinthenon-forestedurbanlandscape.MPBgalleiesarerecognizedaslong,straight,verticalgallerieswitha“j”crookatthebottom.Thegalleriesusuallyextendfrom1to3feetupthetree.OtherDendroctonus species affectanarrowerrangeofhosttrees.ThesewillbemostcommonlyseeninhighelevationlodgepoleandspruceforestsinUtah.
DRYOCETES, PHLOEOSINUS, PITYOPHTHORUS, AND XYLEBORUS BEETLES
OfthefourcommonScolytus beetles in Utah, the elm-feedingEuropeanelmbarkbeetleandthebandedelmbarkbeetlearethemostabundantintheurbanlandscape.TheyarealsomajorvectorsoftheDutchElmDisease(DED)fungus,whichcankillelmtreesorcausechronicillnessandstress.Formorein-depthinformation,pleaseseeourfactsheet“Elm Bark BeetlesandDutchElmDisease.” Theshotholeborercaninfeststressedorinjuredportionsofapple,cherry,pear,andhawthorntreesinUtah.Normally,thisbeetlekillslargertreebranchesratherthanwholetrees.InUtahthefirengraverbeetlecommonlykillsstressedfirtreesinhigh-elevationforests,butcaninfestfirtreescommonlyplantedin the landscape.
ThebeetlesinFigures24-27aremostlyminorpestsinUtah.Thewesternbalsambarkbeetlemostlyattackdiseasedorstressedfirtreesathighelevations,butcouldaffectwhiteandotherornamentalfirsinthelandscape.AllrecordsofPhloeosinusbeetlesinUtaharefromornamentalArizonacypresstreesinWashingtonCounty. Most Pityophthorusbeetlesaffectsmallerlimbsandbranchesondyingorstressedtreesorlimbs.Theyusuallydonotcausetreedeathandarenotapestofconcern.OnenotableexceptionistheWalnutTwigBeetle,whichtogetherwithitstree-killingfungus,ThousandCankersDisease(Geosmithia sp.),haskilledmanyblackandotherwalnutsthroughoutthewestandareasofthemidwestandsoutheast.Together,thebeetleandfungusarethemajorpestofwalnutsintheU.S.FormoreinformationonthisbeetlereadthefactsheetfromColoradoStateUniversity. Xyleborusbeetlesarecalledambrosiabeetlesbecauseoftheambrosiafungustheycarry.Ambrosiabeetlesaredifferentfromotherbarkbeetlesinthattheydonotfeedinthephloemlayer,butboreintothesapwoodofthetree.Onceinthesapwood,theyfeedonthegrowingambrosiafungusinsideoftheirgalleriesfromwhichtheygaintheirnutrition.
CONTROLMechanical/Physical: Keeptreeshealthyandstressfreewithproperdeepwateringandfertilization,especiallyforold,stressedtrees.Insomesituations,treerootsmustcompetewithturfroots or will have deeper root systems than turfandmustbewateredlessfrequentlyforlongerdurations.Soilshouldcontainadequatemoisturetoadepthofabout20inches.Soilmoisturecanbetestedbypushingalongscrew driver or slim metal rod into the soil. The metal will easily penetrate moist soil, and will stop when dry soil is reached. Deep watering totreesshouldbedoneonceaweekduringhotsummermonths(July,August)andlessfrequentlyinthecoolermonths.Theamountofwaterittakestodeepirrigateto20incheswilldependonyoursoiltype(lesswaterforsandysoils,moreforclaysoils),soexperimentwithwateringtimesuntilyourscrewdrivertestshowsmoisturetoadepthofabout20inches.Irrigationatnormalturfvolumesisnotadequatefortreeirrigation.Supplementaloradditional sprinkler irrigation is necessary. For moreinformationonproperwateringclick here. Barkbeetlecontrolmustbepreventativeandshouldbeginwithmonitoringandscouting.Closelyobserveyourtreestocatchhealthissuesbeforetheybecomemajor problems. For more detail on what to lookfor,seethesection“HowdoIKnowifMyTreeisInfested?”above.ConsultyourlocalUSUExtensionofficeortheUPPDLforcurrentinformationonbeetleflightsandspraytiming.
Monitoring/Traps: Lindgrenfunneltrapsusedincombinationwithattractivelures(e.g.,ipstrilure,alpha-pinene,ethanol,etc.)canattractvariousbarkbeetles.Whenbeetlesspecifictoyourhosttree(e.g.,spruceipsandbluespruce)beginshowingupintraps,preventativespraysshouldbeappliedimmediately.Whiletrapscangiveaccurateadultflightinformation,theyalsoattractbeetlestoyourproperty,whichcouldleadtotreeattack.Usetrapsandlurescarefully.Neverlocate traps near host trees as spillover can occur.Itismoreeffectivetovisuallymonitoryourneighborhoodandsurroundingareastoseeiftreeshavebeenkilledbybarkbeetles.Thiscouldindicatethatbeetlesareinthearea,andthatprotectionofhigh-valuetreesmaybeneeded.
Chemical Control: Oncethebeetlesareunderthebarkand have girdled the tree, there are no chemicalsthatwillsavethetree.Preventiveinsecticidesshouldbeappliedbeforebeetlesemergeinspringorearlysummer.Springinsecticideapplicationsshouldoccuroncetemperaturesareconsistentlyover50°F.Atthistemperature,manybarkbeetlescontinuedevelopmentunderthebarkoremergetofindnewhosttrees.Properlytimedandapplied insecticides will kill bark beetles as they chewthroughtheinsecticide-soakedbark,preventingsuccessfulattack.Someproductsarelabeledfortrunkapplicationstoinfestedtreestokillbeetlesastheyemergeorunderthebarktopreventinfestationofadditionaltrees. To date, no systemic insecticides have beenproveneffectiveatpreventingbarkbeetlesfromkillingtrees. Toprotectornamental(non-fruitbearing)treesfrombarkbeetleattackapplya preventative insecticide prior to beetle flight.Sincebarktreatmentsareappliedatahigherratethanforothersites,selectproductslabeledforuseasabarktreatmentonornamentalorforesttrees,dependingonyoursituation.Themosteffectiveactiveingredientsincludecarbaryl,bifenthrin,andpermethrin.Belowareafewexamplesofeach.Linkstoproductlabelsareincluded,butmaybeoutdated.Pleasemakesureyoureadthelabelontheproductyoupurchasebeforeuse.Informationonbarkbeetleprevention/controlcanbefoundnearthebottomoftheproductlabels.
Carbaryl: Group 1A, Carbamates +Carbaryl4L(label) - Type: Generaluse.
- Labeled Pests: To control Dendroctonusbarkbeetlessuchas blackturpentinebeetle,mountainpinebeetle,westernpine tipbeetle,southernpinetipbeetle,andengraverbeetles (Ipsspp.)Alsoforuseonotherbarkbeetlessuchas ambrosia beetles, elm bark beetles, and emerald ash borer.
- Labeled Pests: To control Dendroctonusbarkbeetlessuchas mountainpinebeetle,southernpinebeetle,westernpine beetle,blackturpentinebeetle,andengraverbeetles(Ips spp.)Alsoforuseonotherbarkbeetlessuchasambrosia beetles, elm bark beetles, and emerald ash borer.
- Labeled Pests: To control bark beetles and boring insects (including,butnotlimitedto:ashborer,bronzebirchborer, rhododendronborer,elmbarkbeetlesandturpentine beetles.)
- Application: Stem-infestingbeetles:treatlowerbranchesand trunkpriortoadultemergence.Complete,uniform coverageisneededforbestcontrol.Arepeatapplication may be necessary on a 3 to 4 week interval to prevent severe tree stem damage.
- Notes: Foroutdoorhomeowner(residential)useonly.Best productforusebynon-licensedchemicalapplicators.High poweredsprayequipmentneededforcompletecoverage on larger trees.
Sanitation: Ifanactiveinfestationisdiscoveredinatreeandthetreewilldie,thetreeshouldberemoved immediately and treated to prevent furtherdevelopmentandflightofbeetles.Acommon mistakeistocutdownaninfestedtreeandthenstackinfestedlogsundera
ADDITIONAL RESOURCESIpsBeetles:ColoradoStateUniversityFactSheetMountainPineBeetle:ColoradoStateUniversityFactSheetUSDA Forest Service, Rocky Mt. Research Station WebsiteUtahDivisionofForestry,FireandStateLandsFactSheetUniversityofCaliforniaIntegratedPestManagementProgramFactSheetBarkandWoodboringBeetlesoftheWorldWebsite
nearby host tree. Removing a tree does not kill thebeetlesandtheycanstilldevelopunderthe bark and emerge to attack more trees! Aftercuttinganinfestedtreetherearemultipletechniquesforkillingbeetlesunderthebark: - Debark: Removeallbarkfromthetree.
- Insecticide Spray: Use a labeled insecticide to treat the tree priortoremovalortologsafterremoval.