Twig Pruner Elaphidionoides villosus (F.)<br/> Oak Twig Pruner Elaphidionoides parallelus Newman

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Order	Coleoptera
Suborder	Polyphaga
Infraorder	Cucujiformia
Superfamily	Chrysomeloidea
Family	Cerambycidae
Subfamily	Cerambycinae
Tribe	Elaphidiini

Scientific Name

Anelaphus

Scientific Name Synonyms

Gymnopsyra

Gymnospyra

Common Name

long-horned beetles

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: U.S. Department of Agriculture, Forest Service. Southern Forest Experiment Station; 1986. 31 p.

Importance

The twig pruner, Elaphidionoides villosus (F.) and oak twig pruner, E. parallelus Newman, are found throughout the Eastern United States northward to Canada and westward to Texas, reaching greatest importance in their northern range (Chittenden 1910, Linsley 1963, Moznette and others 1931). They attack pecan and hickory as well as other forest, shade, and fruit trees but show a marked preference for the oaks. The larvae, boring in the stems, cut off or prune twigs and small branches. Pruned twigs drop to the ground or hang loosely from partially severed branches. The ground under heavily infested trees may be littered with fallen twigs and branches. Such pruning and littering adversely affect the aesthetic quality of ornamental plantings and cause clean up problems; heavy twig losses reduce the fruiting area and, in turn, the nut crop; and young trees may be deformed. Injuies to trees in natural stands are seldom serious.

Description

The adult beetles are elongate, slender, and parallel-sided (fig. 16A) (Chittenden 1910, Linsley 1963). The bodies are light to dark brown and clothed with irregular patches of fine gray hairs giving them a mottled appearance. There are spines on the first few joints of the antennae and the tips of the wing covers are notched and bispinose. They range from 12 to 18 mm in length. Elaphidionoides villosus resembles E. parallelus very closely, but E. parallelus is usually slightly smaller and somewhat more slender. The larvae are elongate, cylindrical, and creamy white; they have short rudimentary thoracic prolegs and measure about 14 to 22 mm in length at maturity.

Evidence of Infestation

During the summer, fall, and winter pruned twigs from 8 to 20 mm in diameter and from 20 to 90 cm in length litter the ground under infested trees (Gill 1924, Moznette and others 1931). Pruned twigs may also hang from the crown. The nature of the girdle itself distinguishes the twig pruners from the twig girdler and branch pruner. The cut by twig pruners is made from inside by the larva, which gnaws a circular groove in the wood, leaving only the bark intact. The severed end of the twig presents a smoothly cut surface, near the center of which is an oval 2-mm gallery opening often plugged lightly with frass (fig. 17). A smaller side-twig is usually hollowed out and may be broken in its fall to the ground. There are no egg niches or mandible marks on the bark surface as seen with the twig girdler. Moreover, splitting the freshly pruned twig reveals the nearly grown twig pruner larva inside, while the twig girdler either has not hatched or the larva is too small to be noticed until the following spring and summer.

Biology

The adults emerge from early spring to early summer (Chittended 1910, Gosling 1978). The female deposits her eggs in slits in the bark at leaf axils near the tips of very small green twigs that arise from a larger twig 8 to 20 mm in diameter. The young larva burrows down the center of the twig toward its base, hollowing it out more or less completely. When the larva reaches the larger limb, it bores into the branch and burrows a short distance down the center of the stem. In late summer or fall the larva severs the branch by making concentric circular cuts from the center outward to, but not including, the thin bark. Severed branches later break and fall to the ground with the larvae in them. The larva retreats back into its burrow and plugs the oval gallery at the severed end with small fibrous frass and pupates within the burrow the following spring. There is usually one generation per year, but a 2-year generation life cycle has been reported for E. parallelus in its northern range (Gosling 1978).

Control

Control of twig pruners in orchards, nurseries, and ornamental plantings is similar to that for the twig girdler (Chittenden 1910, Gill 1924). That is, all severed twigs on the ground or lodged in the tree should be collected during fall and winter and destroyed while the grubs are still in the twigs. To be most effective, the severed twigs should be collected over the entire orchard, woodlot, or neighborhood. Insecticides are rarely needed; natural controls help to keep infestation in check. Two braconid parasites, Bracon eurygaster Brulle and Odontobracon elaphivorus Rohwer, have been recovered from the twig pruner (Linsley 1963), while two braconids, Meteorus tibialis Muesebeck and Iphiaulax eurygaster Brulle, one ichneumonid, Agonocryptus discoidaloides Viereck, and one tachnid, Minthozelia ruficauda Reinhard, were reared from the oak twig pruner (Gosling 1978). The downy woodpecker, Dryobates pubescens L., blue jay, Cyanocitta cristata L., and black-capped chickadee, Parus atricapillus L., have been reported to destroy large numbers of the twig pruner (Chittenden 1910). A spider, Theridium tepidariorum C. Koch, has also been observed preying upon the twig pruner. Rodents, such as squirrels, have destroyed up to 31 percent of the oak twig pruner population in Michigan studies (Gosling 1978).