Question of the Week: September 26, 2019

Elm twig has been cut by twig girdler beetle.

“Why are branches falling off my tree? They look like they’ve been cut.”

This is the work of the twig girdler beetle. It’s actually a fascinating life process. The adults are active in late summer into early fall. They mate, and the female uses her mouthparts to encircle small twigs of pecans, elms and many other species, leaving only a small piece of the twig tissue in place.

This photograph from Oklahoma State University shows the twig girdler at work.
Bald cypress twigs are less commonly attacked by twig girdlers, but FB friend Bob M. posted this photo one year ago.

She then deposits a small number (3-10) eggs into the wood of the twig. The eggs hatch, and the larvae develop within the dead twig either while it’s still on the tree or after it falls to the ground. They pupate while still within the twigs and emerge in late summer to start the next life cycle.

Pecans are most common hosts to twig girdler damage. Small branches are falling all around in the Sperry forest currently.

Because the female doesn’t really feed on the tree while she is depositing the eggs, spraying isn’t of much help because you’re not likely to be there when she is active. And there is no spray that will reach the larvae inside the twigs.

Continued Below

By deduction, about your only means of reducing the population is to gather the fallen twigs and burn them or send them off to the landfill. Of course, the hundreds of trees in the neighborhood or in the park or woods around you are going to have their own source of supply, so you’re probably going to be seeing twigs on the ground for years to come.

2019 has started out as an especially active fall season for them. I’ve had a lot of inquiries already.

(Here is a more scholarly outline of all of this from Oklahoma State University.)

Posted by Neil Sperry
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