Twig Girdlers

Paul Thompson, County Extension Agent
Clemson University Cooperative Extension Service

HTG 1216

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Have you been noticing twigs about the diameter of a pencil on the ground beneath your shade trees? Often leaves will still be attached. If you have, your trees have likely been affected by a beetle called a twig girdler.

This beetle occurs over much of the eastern and southern United States from New England to Texas and Arizona. It is most common in the South and is found throughout our state wherever its host trees occur. Pecan, hickories, and persimmon are the favored hosts, but elm, hackberry, basswood, sourwood, oak, honeylocust, dogwood, and some fruit trees may be hosts as well. With pecan trees, heavy infestations may result in low nut yields the following year and sometimes longer.

The best way you tell if the fallen twigs have been caused by a twig girdler is by the neatly severed end of the twig where the adult beetle girdled it part way through. Twigs usually fall to the ground in the fall and winter months.

Adult twig girdler and notched twig.
Adult twig girdler and notched twig.
Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org

This insect belongs to the Cerambycidae family, which are commonly known as long-horned beetles. The 20,000 plus species within this family are wood boring insects known as sawyers or round-head borers because the larval (borer) stage is cylindrical and leaves a round tunnel in the wood. Long-horned beetles are so called because the adult beetles have antennae that are very prominent and are as long (female) or longer (male) than the length of their bodies. The good news is that twig girdlers, although members of an extremely destructive family of beetles, are not serious pests. Among large, established trees, girdling is confined to twigs in the periphery of the crown. In trees with well-developed crowns, loss of a few twigs results in little or no real damage. However, among seedlings and small, young trees, damage could be more noticeable.

The twig girdler requires a full year to complete its life cycle. The adult beetles emerge from previously girdled twigs in late summer to early fall. After mating, the female twig girdler lays, on average, three to six eggs along a twig just under the bark.

Twig girdler egg laid beneath bark.
Twig girdler egg laid beneath bark.
Paul Thompson, ©2016, Clemson Extension

Twig girdler egg notches in bark.
Twig girdler egg notches in bark.
Paul Thompson, 2016, Clemson Extension

She then chews a notch completely around the twig leaving a core of wood intact. The girdled twig later breaks off and falls to the ground.

Neatly severed branch by twig girdler.
Neatly severed branch by twig girdler.
Paul Thompson, ©2016, Clemson Extension

There are four life stages: egg, larva, pupa, and adult. The eggs normally hatch within the fallen twig in October to November. The larvae are off-white with a light brown head. 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. 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.

Adults are approximately ½ inch long, dull gray with white markings and have very long antennae. Their coloration is muted and blends well with the bark of trees making them difficult to see. Female beetles live six to ten weeks and will lay from 50 to 200 eggs before they die.

Controlling twig girdlers with pesticides is usually impractical since they are normally not a serious problem, and it would be next to impossible to keep a pesticide residue on plants to protect them over the six to 10-week period of adult activity, much less to try to spray all the twigs in a large tree. The best and most effective way to reduce populations is to collect the fallen twigs in the fall and winter and burn them to destroy the larvae.

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