Twig Girdle Oncideres cingulata (Say)

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	Lamiinae
Tribe	Onciderini
Subtribe	Onciderina
Genus	Oncideres

Scientific Name

Oncideres cingulata

Scientific Name Synonyms

Oncideres cingulatus

Common Name

twig girdler

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 twig girdler, Oncideres cingulata (Say), a pest of pecan and hickory, and to a lesser extent several other hardwood species, is found most commonly in the Southern States but is known as far north as New England and westward to Arizona (Gill 1924, Herrick 1904, Beal and Massey 1942). The adult beetles girdle twigs and small branches causing the injured portions to break away or hand loosely on the tree. It is not uncommon to see the ground under infested trees almost covered with twigs that have been cut off. This affects the beauty and aesthetic quality of ornamental plantings. The fruiting area of heavily infested trees is often greatly reduced, resulting in low nut yields the following year and sometimes longer. This type of injury causes the development of many offshoots that adversely affect the symmetry of the tree. Pecan nurseries located close to heavily infested woodlots occasionally suffer considerable loss from girdled seedlings. Repeated girdling of terminals causes forks, crooks, and other stem deformities in young timber plantations as well as in natural reproduction (Kennedy and others 1981).

Description

The adults are typical long-horned beetles that range from 12 to 16 mm in length (fig. 13A) (Bilsing 1916, Gill 1924, Herrick 1904). The body is cylindrical and generally grayish brown with a broad, ashy-gray band across the middle of the wing covers. The eggs are white, elongate oval, and about 2.5 mm in length. The larvae are whitish, cylindrical, legless grubs that reach 16 to 25 mm in length at maturity (fig. 13B). The pupae are white with short, dark spines on the dorsal sides of segments.

Evidence of Infestation

The presence during late summer and fall of severed twigs on the ground, handing loosely attached or lodged in the canopy is good evidence of infestation (Gill 1924, Herrick 1904). Most girdled twigs are from 6 to 12 mm—occasionally ranging up to 18 mm—in diameter, and 30 to 60 cm in length. The nature of the girdle itself distinguishes the twig girdler from other branch pruners. The cut by the twig girdler is the only one made from the outside by the adult beetle and has been described as a uniform V-shaped cut (fig. 13A). The cut is seldom complete, leaving a small center with a jagged surface caused by the break. Since the twigs are girdled while the leaves are present, the severed twigs retain the brown leaves for some time (fig. 14). Severed twigs lodged in the tree canopy or on the ground often retain leaves even after the tree sheds its leaves in the autumn. Close inspection of the severed twigs will reveal tiny egg niches and many mandible marks or grooves mane in the bark by the female beetles. Large trees usually sustain the most girdling, but young plantation trees are sometimes heavily damaged (fig. 15).

Biology

The adults emerge from late August to early October (Bilsing 1916, Gill 1924, Herrick 1904). They feed on the tender bark near branch ends and mate before ovipositing and girdling the twigs. The branches are apparently girdled by the female so that congenial conditions will be provided for the development of the larvae, which are unable to survive in living twigs. The girdling extends through the bark and well into the wood in a complete circle around the stem and leaves only a thin column of the center wood attached, which breaks easily. Eggs are laid during or after the cutting process, but never before the beetle makes part of the cut. They are inserted singly beneath the bark or slightly into the wood, usually near a bud scar or adjacent to a side shoot. The number of eggs per twig varies from 3 to 8 but may range up to 40. Adults live 6 to 10 weeks. Females deposit 50 to 200 eggs each, which hatch in about 3 weeks. After overwintering, the larvae grow rapidly in the spring and tunnel toward the severed end of the twig by feeding only on the woody portion and leaving the bark intact. A few small circular holes are made in the bark to eject pellets of frass and excrement. The mature larvae close off the gallery with shredded fibers to form a pupation chamber. Pupation occurs during August and September and lasts 12 to 14 days. The adult chews a circular hole in the bark to emerge. There is one generation per year.

Control

In orchards, nurseries, and ornamental plantings, the severed twigs on the ground as well as those lodged in the trees should be gathered and burned during the fall, winter, and spring when the eggs and grubs are in the twigs (Gill 1924, Moznette and others 1931). The same practice should be followed in nearby woodlots when plantings in the vicinity have a history of serious damage from this insect pest. Insecticides may be necessary to prevent damage from heavy infestations, although they are probably unnecessary in natural forest stands. Natural controls are important in keeping twig girdler popualtions low; desiccation of the eggs is apparently the greatest single decimating factor. Three parasites: an eurytomid, Eurytoma magdalidis Ashm., one ichneumoid, Iphiaulax agrili (Ashm.), and one eulophid, Horismenus sp., help to reduce the girdler population (Beal and Massey 1942). A clerid predator, Cymatodera undulata Say, has also been reared.