The eggs are white, elongate oval, and about 3/32 inch in length. The larvae are whitish, cylindrical, legless grubs that reach 5/8 to 1 inch long. The pupae are white at first with short, dark spines on the top sides of the abdominal segments.
During late summer and fall, the presence of severed twigs on the ground or hanging loosely attached or lodged in the canopy is good evidence of twig girdler activety. Most girdled twigs are from 1/4 to 1/2 inch (occasionally up to 3/4 inch) in diameter, and 10 to 30 inches long. 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 a beetle and is seldom complete, leaving a small central cylinder (this leaves a central jagged area when the twig breaks). 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. Since the twigs are girdled while the leaves are present, the severed twigs retain the brown leaves for some time. 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 made in the bark by the female beetles. Large trees usually sustain the most girdling, but young trees are sometimes heavily damaged.
The adults emerge from late August to early October. 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 proper conditions will be provided for the development of the larvae. 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 new adult chews a circular hole in the bark to emerge. There is one generation per year.
In orchards, nurseries, and ornamental plantings, the severed twigs on the ground as well as those lodged in the trees should be gathered and destroyed during the fall, winter, and spring when the eggs and grubs are in the twigs. The same practice should be followed in nearby wood lots containing oak and hickory when nearby plantings have a history of serious damage from this insect pest. Populations can be greatly reduced in one or two seasons.
Insecticide is rarely justified or practical. Insecticides may be necessary to prevent damage from heavy infestations in some hardwood tree nurseries. These may be applied once or twice in September and again in October as a protectant to reduce the majority of the twig girdlers. Natural controls are important in keeping twig girdler populations low. Desiccation of the eggs is apparently the greatest single mortality factor. The parasites, Eurytoma magdalidis, Iphiaulax agrili, and Horismenus sp., and a checkered flower beetle, Cymatodera undulata all help to reduce girdler populations.
Auburn University note with pictures of all stages.
Published by North Carolina Cooperative Extension Service
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
© 2001 NC Cooperative Extension Service
Prepared by: James R. Baker and Stephen Bambara, Extension Entomologists
ENT/ort-96 October 1997 (Revised) 2001
Web page last reviewed January, 2011 by the webperson.