Name of Article

Name of Article:

Elaphidionoides villosus (Fabricius)

OR

Anelaphus villosus (Fabricius)

Oak Twig Pruner

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''Author: Robin Baj, Faculty of Forestry, University of Toronto''

=Identification=

Larvae are white and segmented, reaching typical lengths of 12-21mm (0.5-0.8 inches) at maturity. Each mature larva has distinctive yellow hairs on its prothorax, directly behind its head.¹

Adults are greyish-brown, slim, and elongate; ranging from 12mm to 18mm (0.5-0.75 inches) long. The dorsal side has patches of grey hairs, giving the insect a mottled appearance.² Spines are present on the first several joints of their lengthy antennae, as well as on the tips of their elytra.³

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See the “Damage” section for types of evidence that may indicate an oak twig pruner infestation.

=Geographic Distribution=

Oak twig pruner affects forests of eastern North America.⁴

=Hosts=

Oak is the preferred host (several species, including white oak), though many other hardwoods can also be affected. These include hickory, walnut, elm, sweet gum, pecan, locust, maple, and hackberry.²

=Damage=

Infestations of oak twig pruner can be very aesthetically damaging, and may sometimes result in tree deformities or retardation of development. Tree death, however, is a very rare consequence.²

Damage is inflicted by the insect’s larval form, which bores through twig centers. Branch tips with fading and browning foliage are one of the initial indicators of infestation.⁵ Infestation becomes more obvious when small branches begin to break off where the pruner has weakened them most (see the “Life Cycle” section). These pruned branches can range from 30-100cm (12-40 inches) in length and 6-25 mm (0.25-1 inches) in diameter.⁴ They tend to accumulate quickly underneath affected trees, but sometimes may not break off completely, and may droop or hang instead.

A tell-tale sign that oak twig pruner may be behind observed tree damage is if the severed twigs have a smooth end surrounded by jagged bark, with an oval-shaped hole in the center. This hole leads to the pruner’s longitudinal gallery, and is usually plugged with frass.⁶

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=Life Cycle=

Adult beetles emerge in late spring when oak leaves are starting to form. Females lay their eggs in holes chewed into bark at leaf axils of twig tips (one egg per twig).³ When the eggs hatch, the larvae bore into their twigs and feed just beneath the bark.¹ Eventually they bore into the center of the stem and down towards the stem base. In late summer and early autumn, the larvae move outward from the center and make concentric circular cuts through the wood, but spare the bark.⁵ These weakened branches break and fall to the ground very easily, even under slightly windy conditions. The larvae then retreat back into their galleries in the twig centers and plug the smooth “pruned” ends with frass.⁶ Here they can continue to feed and are protected from the elements and natural enemies.

Larvae may pupate in either the fall or the spring², meaning that overwintering may occur in either a late instar larval or a pupal form. There is only one generation per year.

=Population Dynamics=

Oak twig pruner tends to be a chronic problem, but was particularly damaging in New York State in 1993 and 1994.¹ An outbreak was also reported in Michigan in 2006, when oak branches were found piling up on lawns at an alarming rate.⁶

=Control and Management=

The best method of control is to gather broken twigs off of the ground in the fall, winter and very early spring and to then destroy them (often accomplished by burning).³ The purpose of this is to eliminate larvae and pupae before they have a chance to emerge as adults and reproduce.² Similarly, it is important to collect and destroy any hanging or lodged branches remaining on the trees, because sometimes infested twigs do not completely break off. Selective pruning can also help if infested twigs can be identified.³ Repeated removal and destruction will keep beetle populations low.

Insecticides are not recommended because they would need to be persistent and very thoroughly sprayed in late spring, when adults are emerging. It would not be effective to spray at other times of the year, considering that the rest of the oak twig pruner’s life cycle is spent inside branches.⁶

=References=

(1) [http://www.dec.ny.gov/docs/lands_forests_pdf/oakprune.pdf Allen, D.C. 1995. The Oak Twig Pruner. ''New York Forest Owner'', Mar/Apr 1995: 14-15] [accessed 20 March 2009]

(2) Drooz, A.T.1985. <u>Insects of Eastern Forests</u>. U.S. Department of Agriculture Forest Service, Washington, D.C.

(3) [http://entoplp.okstate.edu/Pddl/2007/PDIA6-26.pdf Mulder, P. 2007. Twig Pruner and Girdler, Identification and Management. ''Plant Disease and Insect Advisory'' 6(26): 3-5.] [accessed 20 March 2009]

(4) Solomon, J.D., McCracken, F.I., Anderson, R.L., Lewis Jr, R., Oliveria, F.L., Filer, T.H. and P.J. Barry. 1987. <u>Oak Pests: A Guide to Major Insects, Diseases, Air Pollution and Chemical Injury</u>. U.S. Department of Agriculture Forest Service, Washington, D.C.

(5) [http://www.mortonarboretumphc.org/PHC%20report%20pdfs/070706%20Issue%2012.pdf Terrell, C. 2006. This week’s sightings: Oak Twig Pruner. ''Plant Health Care Report'', 1(12): 3-4.] [accessed 20 March 2009]

(6) Russell, H. and J. Smith. 2006. Small oak branches littering yards across the Lower Peninsula. ''Landscape Alert'', 21(13): 5. Available from http://www.ipm.msu.edu/cat06land/l07-14-06.htm [accessed 20 March 2009]