–LastupdatedJanuary2017–

BIOLOGY,DISTRIBUTION,KEYCHARACTERISTICSDistribution of black stem borer in Michigan. The black stem borer,Xylosandrusgermanus(Blanford),isanintroducedpestthatwasfirstfoundintheUnited States in New York grapes in the 1930’s (1). It was first reported inMichiganin1980andisnowwellestablished.A2015trappingsurveyconductedby theTreeFruitEntomologyprogram foundblack stemboreradults inall themajortreefruitproducingcountiesinMichiganwiththehighestcaptureratesinSouthwestandFruitRidgesites.

Blackstemborerbiology. Overwinteringadultsare found ingalleriesat thebaseof infested treesandbecomeactive in lateAprilorearlyMay,afteroneortwoconsecutivedaysof68°Forhigher,oftencoincidingwithbloomingforsythia(6).Adultsareabout2mm(0.08in.)longandfemalesoutnumbermalesby10to1.Onlythefemalesareknowntofly,andoncematedtheyboreintoyoungtreesto createbrood chambers consistingof a seriesof tunnels and chambers calledgalleries. The entrance to each tunnel is about 1mm (0.04 in.) in diameter andcontinues horizontally into the sapwood for about the length of the female’s body. At that point, the tunnelbranches off into one ormore chambers, sometimes into the heartwood. Female stemborers carry a symbioticfungus(Ambrosiahartigii)ontheirbodiesthattheyusetoseedthegalleriesinwhichtheylaytheireggs(Figure1).Thegrowingfungusprovidesallthefoodneededforthedevelopinglarvaeaswellasfortheadults.

Black stem borer adults are attracted to stressed trees although they have been known to infest trees do notappear to be stressed (2). Injured trees produce ethanol, which is attractive to this beetle. Black stem borersgenerallyprefertreesthatare4inchesorlessindiameter.Hostplantsoftheblackstemboreraremany,includingforest andornamental species.Thebeetles invadeorchards from theedgeandare found ingreaternumbers inneighboringwoods.Theyareknowntofly100meters(328.1ft.)ormoretocolonizenewtrees(3).

Blackstemborerlifecycle.Femaleblackstemborerscomeoutofoverwinteringandbeginflyinginsearchofnewtreestoinfestin late April or early May. Within the galleries created by themated female, eggs are laid at the rate of oneperdaywith eachfemaledepositingupto18eggs.Larvaehatchfromtheeggs6dayslater at 24°C (75.2°F) (4). There are three larval stages, all ofwhich are passed within the brood chamber, feeding on theambrosia fungus growing in the galleries. Larval developmenttakesabout12days,thepupalstagetypicallylasts7days,andthetimefromeggtoadultisabout25daysat24°C(4).Itislikelytheyhave2generationsperyear inMichigan.TheseasonalpatternofblackstemboreradultflightinMichiganisshowninFigure2.

Figure1.Broodgallerieswhereeggsarelaidandlarvaedevelop.WhitishmaterialisAmbrosiafungus,whichisthefoodforbothlarvaeandadults.Photo:BillShane.

Managing Black Stem Borer in Michigan Tree Fruits

Michael Haas1, Julianna Wilson2, Larry Gut2, 1Trevor Nichols Research Center, 2Department of Entomology

Photo:MikeHaas

Formoreinformation,see:Agnello,A.,D.Breth,E.Tee,K.CoxandH.R.Warren.2015.Ambrosiabeetle–Anemergentapplepest.NewYorkFruitQuarterly.23(1):25-28.

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Figure2.Seasonalcapturesofblackstemborerinethanol-baitedtrapsinMichigan,2016.

2 MANAGINGBLACKSTEMBORERINMICHIGAN

MONITORING&MANAGEMENTMonitoring.Look for signs of infestation on the trees, including 1mm diameterentrance holes with sawdust toothpicks protruding from them (Figure 3), darkdiscoloration on the bark, oozing sap, and dry, blistery bark. Use a simple trap tomonitorfemaleactivityinthespring:cut2-4windowsinthebodyofaplastic1or2-literbottlethathasacap(Figure4).Hangitupsidedownataheightof0.5m(1.6ft.),intheorchardedgenearwoodedareas(5).Baitthetrapwithethanolusingoneofthefollowingmethods:

1. Squirtaboutaquartercupofethanol-basedhandsanitizer(unscented)intothecapend(bottom)ofyourtrap.Ifusingthismethod,trapsmustbecheckeddailybecausethesanitizerwillformacrustonthesurfaceafter24hours.

2. Pouracupofcheapvodkaintothecapendofthetrap.

3. Purchaseaready-madeethanollure(StandardReleaseethanollures,AgBio,Inc.,Westminster,CO)tohanginsidethetrapandfillthebottomofthetrapwithsoapywaterorasmallamountofantifreeze.Ifusingthismethod,trapsshouldbecheckedatleastonceperweek.

These beetles are very tiny and require the use of a microscope and training toidentify them correctly to species. Your localMichigan State UniversityExtensionfruiteducatorcanhelp.

Management.The time to sprayan insecticide for thispest iswhen femalesareflying in thespringbeforecolonizingnewtrees.Young treesnear theperimeteroforchards,especiallynearwoodlots,areatgreatestriskofinjury.Becausetheyaresotiny, it isdifficult tomonitorforadultstodeterminetheoptimumtimetoapplyaninsecticide,butatrapasdescribedabovecanhelptimeapplications.

Pyrethroid insecticides applied as trunk sprays, have shown the most promise inreducingthenumberofnewinfestationswithinaseason(7).Theapplicationofbio-repellentsappliedtotrunksofstressedtreesmayalsoreduceinfestation.AlthoughnotregisteredspecificallyforblackstemborercontrolinMichigan,permethrinisaneffectivematerialforreducingthenumberofnewtreesattackedinthespring.Inapples,greenfruitwormandspottedtentiformleafminersareinsectslistedonthepermethrinlabelandcommonlyoccuraroundthesametimeasthespringblackstemborerflight(Figure2).Applebloomoccursnearthistimealso,soprecautionsmustbetakentoprotectpollinators.

Unlike sprays forotherborers, systemic insecticidesarenot recommendedagainst thispestbecause larvaeandadultsinbroodgalleriesfeedontheambrosiafungus,notplanttissue.

Laterintheseason,thebestmanagementstrategyistoremoveandburntreesthatare75percentormoredeadordying.It isalsoimportanttomakesurethatall largepruningsandbrushpilesareeitherburnedorchippedandcompostedaspilesofpruningsandchips,havebeenimplicatedassourcesofnewinfestations.

Figure3.Sawdusttoothpicksprotrudingfromblackstemborerentryholes;windandraineasilyknockthemoffthetrees.Photo:MikeHaas.

Figure4.Simpletrap;invertedjuicecontainerwithsidescutaway.Photo:MikeHaas.

REFERENCES1.Felt,E.P.1932.Anewpestingreenhousegrowngrapestems.J.Econ.Entomol.25:418.2.Weber,B.C.1982.ThebiologyoftheambrosiabeetleXylosandrusgermanus(Blandford)(Coleoptera:Scolytidae)anditseffectsonblackwalnut.Ph.D.

Dissertation,SouthernIllinoisUniversity,Carbondale,IL.222p.3.Reding,M.E.,C.M.Ranger,B.J.Sampson,C.T.Werle,J.B.OliverandP.B.Schultz.2015.MovementofXylosandrusgermanus(Coleoptera:Curculionidae)in

ornamentalnurseriesandsurroundinghabitats.J.Econ.Entomol.,108(4):1947-1953.4.Weber,B.C.,andJ.E.McPherson.1983.LifehistoryoftheambrosiabeetleXylosandrusgermanus(Coleoptera:Scolytidae).Ann.Entomol.Soc.Am.76:455–

462.5.Reding,M.,J.Oliver,P.SchultzandC.Ranger.2010.Monitoringflightactivityofambrosiabeetlesinornamentalnurserieswithethanol-baitedtraps:Influence

oftrapheightoncaptures.J.Environ.Hort.28:85–90.6.Reding,M.E.,C.M.Ranger,J.B.OliverandP.B.Schultz.2013b.MonitoringAttackandFlightActivityofXylosandrusspp.(Coleoptera:Curculionidae:Scolytinae):

TheInfluenceofTemperatureonActivity.J.Econ.Entomol.106(4):1780-1787.7.Reding,M.,J.Oliver,P.Schultz,C.RangerandN.N.Youssef.2013a.Ethanolinjectionofornamentaltreesfacilitatestestinginsecticideefficacyagainstambrosia

beetles(Coleoptera:Curculionidae:Scolytinae).J.Econ.Entomol.106(1):289-298.