Red-Shouldered Shothole Borer Xylobiops basilaris (Say)<br/> Apple Twig Borer Amphiceris bicaudatus (Say)

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Order	Coleoptera
Suborder	Polyphaga
Infraorder	Bostrichiformia
Superfamily	Bostrichoidea
Family	Bostrichidae
Subfamily	Bostrichinae
Tribe	Xyloperthini
Genus	Xylobiops

Scientific Name

Xylobiops basilaris

Common Name

redshouldered bostrichid beetle

Solomon, J. D.; Payne, J. A. A guide to the insect borers, pruners, and girdlers of pecan and hickory. Gen. Tech. Rep. SO-64. New Orleans, LA: USDA Forest Service. Southern Forest Experiment Station; 1986. 31 p.

Importance

The red-shouldered shothole borer, Xylobiops basilaris (Say), and apple twig borer, Amphiceris bicaudatus (Say), are found throughout the United States east of the Rocky Mountains and in southern Canada (Baker 1972, Gill 1924, Moznette and others 1931). Pecan and hickory are among their favored hosts, but they also attack several other deciduous hosts. They generally attack severely stressed and dying or recently dead trees. Trunks of healthy trees growing in close proximity to heavily infested trees are occasionally attacked but seldom with success; however, A. bicaudatus may tunnel the twigs and small branches causing them to wither and die back. Although these borers may cause some twig dieback and possibly hasten the death of trees already stressed or dying from other causes, the threat to healthy living trees is minimal

Description

The adults of X. basilaris are 3 to 5 mm long, black, and bullet-shaped, with many small punctures over the body. The basal part of the elytra is dull reddish or yellow-hence the name "red-shouldered." The wing covers end in an oblique angle at the posterior end, the edges of which are armed with three conspicuous teeth on each side. The adults of A. bicaudatus are similar to X. basilaris except they are larger, range from 6 to 11 mm long, are dark brown, and lack the reddish marking on the wind covers. The larvae of both species are white and C-shaped; when full-grown, X-basilaris is about 5 to 6 mm long and A. bicaudatus is 6 to 12 mm long. The head of the larva is globular and greatly enlarged into the prothorax, the mouthparts extend forward, and there are three pairs of thoracic prolegs.

Evidence of Infestation

The adults of X. basilaris make small round exit holes 2 to 3 mm in diameter; the holes of A. bicaudatus are 3 to 4 mm in diameter and generally much less numerous (Payne and others 1979, Baker 1972, Gill 1924). The holes give a tree trunk the appearance of having been hit by birdshot, hence these borers are often referred to as "shothole" borers. Light sawdust particles may be observed coming from the holes. The borings or frass of the larvae are very fine and powderlike in appearance; they are firmly packed or compressed within the galleries, which run parallel with the grain of the wood (fig. 25). Trees cut back so severely that the trunk becomes saturated with sap are susceptible to infestations by X. basilaris. Twigs that have withered and brown leaves usually contain single, round entrance holes 2 to 4 mm in diameter adjacent to a bud or leaf base. Dissection of the twigs usually reveals a hollow twig that is often occupied by a single adult beetle from late fall to late spring.

Biology

Adults emerge during the summer and fly in search of suitable host trees where they bore through the bark and into the sapwood (Gill 1924, Lugger 1899, Baker 1972, Dean 1920). Tunnels are constructed across the grain just under the wood surface in the sapwood. These tunnels may completely girdle small-diameter limbs and trunks. Eggs are deposited at intervals along the sides of the tunnel. The larvae feed mostly in the sapwood and to some extent in the heartwood. Larval mines run parallel with the grain and are packed with fine, white, powderlike dust. Feeding may continue until the wood is quite dry. The winter is spent mostly as mature larvae in mines; larvae pupate and emerge as adults the following spring and summer through circular holes cut in the bark. Adults of A. bicaudatus often bore into twigs for food and shelter and commonly spend the fall, winter, and spring in galleries within the twigs. A generation can develop from egg to adult in 1 year under optimum conditions, but longer periods of time are sometimes required.

Control

These borers present little threat to healthy well-kept trees; therefore, good cultural practices should be followed to maintain tree vigor (Dean 1920, Moznette and others 1931). Sources of infestation can be eliminated by promptly removing and destroying all dean and dying twigs and branches, prunings, and dead trees.