Camphor Shot Borer: A New Nursery And Landscape Pest In .

ANR-ENT-01-2012SP 742Camphor Shot Borer:A New Nursery and LandscapePest in Tennessee

Camphor Shot BorerA New Nursery and Landscape Pest in TennesseeJason Oliver, Nadeer Youssef, Joshua Basham, and Alicia Bray (Tennessee State University), Kenneth Copley(USDA-APHIS-PPQ), Frank Hale, William Klingeman, and Mark Halcomb (University of Tennessee), andWalker Haun (Tennessee Department of Agriculture)Introductionfungi (ambrosia), which they subsequently introduceinto the tunnels (galleries) when boring into the tree(Fig. 3). The ambrosia fungi grow in the galleries andserve as food for adult beetles and developing young(i.e., larvae).The camphor shot borer, (Cnestus mutilatus[Blandford]), (CSB) (Fig. 1) is a beetle pest native toAsia.Fig. 1. Female (left) and male (right) camphor shot borer (CSB).Fig. 3. Cross-section of a CSB gallery showing eggs and whitecolored ambrosia fungus.The beetle was first detected in the United Statesin Oktibbeha County, Mississippi in 1999. It isnow known to occur in Alabama, Florida, Georgia,Louisiana, North Carolina, Ohio, Tennessee, Texasand West Virginia. In Tennessee, the CSB was firstdetected on April 25, 2008 near a lumber facility inWayne County. As of 2012, CSB has been trapped in18 Tennessee counties (Fig. 2) and probably occurs inother Tennessee counties. The CSB most likely enteredthe U.S. in some type of wood packing material. In theU.S., nursery stock and firewood are other likely meansof transport.Male CSB do not fly, so all new tunnels in the trunk areinitiated by females (Fig. 4). On the tree trunk surface,the gallery entrance appears as a small round hole (Fig. 4).Fig. 4. Left photo: Adult female CSB boring into a tree branch.Right photo: Gallery entrance hole recently excavated in thebranch. The rear of the female CSB is visible inside the galleryentrance.Fig. 2. Tennessee counties with known infestations of CSB in2012.CSB BiologyThe CSB belongs to a group of wood-boring beetlescalled the ambrosia beetles. All ambrosia beetles carry2Temperature influences CSB developmental rate fromegg to adult, which may take as little as 5 to 6 weeksin warm weather. Male CSB are believed to stay inthe gallery, where they likely mate with siblings beforeeventually dying. Females may remain in the galleryto over-winter or may emerge and begin attacking newplants.

When to Expect CSB Activitylargest drill bit size (i.e., 3/32-inch [2.4 mm]) does notfit into CSB galleries.In Mississippi, CSB flight begins in March, and is highfrom April to June (peaking in April), has a secondsmaller peak in August, and ends in September.In Tennessee during 2010 to 2012, CSB attackedcontainerized trees used in research experimentsduring April and May and were captured on trapsthroughout the summer. A Tennessee producerduring 2012 had CSB attacks on dogwood trees duringMarch. The CSB flight patterns and tree attack timingin Tennessee to date suggests mid-March to June asthe period with the highest risk to trees and greatestpossible need for preventative treatments. CSB isreported to have one generation per year in Japan, butthere may be more than one in the southern U.S.Fig. 5. A 5/64 inch (2 mm) drill bit can be inserted into a CSBgallery.Sawdust from CSB boring activity may sometimes beobserved on the branch or at the base of the tree (Fig. 6).The CSB as a Plant PestThe likelihood of CSB becoming an important pest ofnursery and landscape plants is still undetermined,but CSB has many host plants that include commonnursery plants (Table 1). Sweetgum appears to be apreferred host. CSB attacks have been associated withplant stressors like herbicide injury, poorly drainedsoil, trunk and branch damage, and inadequatelymanaged container production. During 2012,containerized dogwood trees under CSB attack ata Tennessee nursery were both under-watered andgrowing in a container substrate with little to no airspace. CSB attacks have been artificially induced onblack walnut, goldenraintree, red maple, sweetbaymagnolia, tulip poplar, and white oak by injecting treetrunks with ethanol. Ethanol is naturally produced bystressed trees and is used by ambrosia beetles like CSBto locate trees suitable for attack. Plants infested withCSB may display symptoms similar to other ambrosiabeetles (e.g., granulate ambrosia beetle), including leafwilting, branch dieback, and tree death. Even if treessurvive CSB attacks, their value as nursery plants willbe reduced by the large entrance holes on the trunksand branches.Fig. 6. Left Photo: Sawdust from CSB boring activity.Right Photo: Sawdust at base from boring activity of multipleambrosia beetles.Some ambrosia beetles that attack nursery plantswill produce toothpick-like strands of sawdust andexcrement from the gallery entrance (Fig. 7). CSBgalleries may also have these toothpick strands butbecause the diameter of the gallery entrance is larger, thestrands usually break off before they become obvious.Fig. 7. Toothpick-like strands of mixed sawdust and excrementextending from non-CSB ambrosia beetle galleries.Recognizing CSB Tree AttacksTree trunks may have sap stains (i.e., bleeding) nearthe site of attack (Fig. 8).Relative to other species, the CSB is a large ambrosiabeetle, and therefore produces a large entrance hole(Figs. 4, 11, and 12). A 5/64-inch (2 mm) drill bit willfit into the entrance of a CSB gallery and is a quick wayto check the hole-size in the field (Fig. 5). The next3

CSB adults have been reported to block the galleryentrance with their body, possibly to protectdeveloping larvae from natural enemies (Fig. 10).Fig. 8. Sap accumulation at theentrance of a CSB gallery and stainson the trunk resulting from sapdraining below the gallery.Fig. 10. CSB abdomen tip blocking the entrance to the gallery.Although CSB are large ambrosia beetles, the beetlespreferentially attack smaller branches (0.8 inchesor less) at about chest level height, which is wherescouting should be focused. The affinity of CSB forsmaller-diameter stems increases concerns that CSBcould become a significant economic and aestheticpest of both nursery-grown plants and landscape trees.Inside the gallery, the wood may develop dark stainsfrom the ambrosia fungi (Fig. 9). Unlike otherambrosia beetles, which generally bore straight into thetree trunk, the CSB gallery typically consists of a shorthorizontal entrance that branches into long verticaltunnels (up to 1.5 inch [3.8 cm] long) (Fig. 9). It is notuncommon for CSB adults to tunnel up and down thepith of small trees, which could weaken the structuralintegrity of the tree.CSB GalleryIdentifying CSB AdultsTo determine if beetles attacking trees are CSB, a knifecan be used to cut the beetle from the gallery. Cuttingoff the branch near the gallery entrance may facilitateCSB extraction. The adult female CSB is a large beetlerelative to other common ambrosia beetles (Fig. 1112). Unlike other ambrosia beetles, female CSB havean abdomen that is shorter in length than the thorax,appearing ‘squashed’ (Fig. 13).Non- CSB GalleryFig. 9. Left photo: Tree branch cut open to reveal internalstructure of a CSB gallery. Note the tunnels that go up anddown the inside of the branch and the black staining insidethe galleries. Right photo: Tree branch cut open to show thegallery of a non-CSB ambrosia beetle species.Fig. 11. Top to bottom: CSB (largest beetle), yellow-bandedtimber beetle (Monarthrum fasciatum Say), granulateambrosia beetle (Xylosandrus crassiusculus Motschulsky),black stem borer (Xylosandrus germanus Blandford), and thefruit tree pinhole borer (Xyleborinus saxesenii Ratzeburg).CBS adults have been reported to block the galleryentrance with their body, possibly to protectdeveloping larvae from natural enemies (Fig. 10).4

Fig. 12. Gallery entrance holes ona dogwood tree. The larger bottomhole is a CSB gallery and the upperhole is another ambrosia beetlespecies. Note the size differenceand also the CSB abdomen tipblocking the gallery entrance.Fig. 14. Left photo: CSB adult with a gap between basal legsegments of the first pair of legs. Right photo: Non-CSBambrosia beetle with no gap between basal leg segments of firstpair of legs.Managing CSBWe currently know very little regarding managementof CSB with insecticides. Insecticides will not likelybe effective once CSB have entered a tree. Insecticidescontaining permethrin as an active ingredient havebeen the most effective for controlling other problemambrosia beetles, but permethrin has not been testedagainst CSB. If insecticides are used, they should bethoroughly applied to the upper trunk and brancheswhere CSB prefer to attack. March to June is theperiod when CSB attacks are most likely. Spraysapplied during March to June would also coincidewith the primary flight periods of other pest ambrosiabeetles like the granulate and black stem borer (Fig.11), so treatments at this time may protect againstmultiple ambrosia beetles. Destroying infested plantsand injured and unsalable nursery stock will alsoreduce future CSB emergence at the nurseries andalso lessen human-assisted spread of CSB throughthe movement of plant materials. However, CSB isreported to be a strong flier, and it will probably bedifficult to prevent re-infestation of nursery plantswhen CSB originate from areas outside the nursery.The best prevention for CSB is likely to be growingtrees that are adapted to a given site location andfollowing good cultural practices that promote plantvigor and reduce stress.Fig. 13. CSB have a shorter abdomen than the thorax, which isunusual for most beetles.The compressed abdomen can be seen without ahand lens if you have good eyesight. If you needadditional assistance with CSB identity, you can takethe specimen to your local county extension office.Another CSB character that can be viewed with amicroscope is the presence of a small gap betweenthe basal segments of the front pair of legs (Fig. 14).The gap character is not exclusive to CSB, but it coulddistinguish it from species that lack a gapIn general, if the ambrosia beetle is large relatively toother ambrosia beetles (Fig. 11), has a compressedabdomen, black color, and the gap is present betweenthe base of the front legs, the beetle is most likely CSB.5