Stick It to Cankerworms

Editor’s Note: This is a guest post by Steve Frank, an assistant professor of entomology at NC State. You can learn more about the Cankerworm Project here, and keep up with Steve’s entomological pest alerts and updates by following @OrnaPests on Twitter.

In spring 2012, a cankerworm outbreak occurred in many North Carolina cities. Students became tangled in hundreds of silk threads that dangled over sidewalks, and were often covered in caterpillars as they walked to class.

I got a lot of calls and emails from landscapers and arborists wondering why there were so many caterpillars. “Are these cankerworms?” they would ask. “Will my trees die? What can I do?” This year we are conducting experiments on campus to understand the biology of these caterpillars and how to reduce their abundance and damage to trees.

The caterpillars stuck to your sweater and hair last year were cankerworms. Spring cankerworm (Paleacrita vernata) and fall cankerworm (Alsophila pometaria) are different species but have very similar characteristics. They both feed in the spring on the leaves of many different deciduous trees. Willow oak was the tree species most heavily infested in Raleigh, Charlotte, Durham, and other North Carolina cities. Cankerworms can completely defoliate trees but last year it was most common for affected trees to lose 10-50 percent of their leaves. A year or two of defoliation will not affect the long-term health of large trees. However, they will be ugly the year they are defoliated and it causes extraordinary concern among the public.

Spring and fall cankerworm eggs hatch in early spring and caterpillars feed for 5-6 weeks. They spend the rest of the summer pupating in mulch and leaf litter beneath trees. In October or November fall cankerworm adults emerge from pupae and climb up the trunk of nearby trees. They lay clusters of eggs in twigs then die. Spring cankerworms climb up trees in spring to lay eggs.

The female moths of both species climb because they do not have wings. Therefore, we are testing “sticky bands” as a way to reduce cankerworm abundance and damage. Sticky bands capture moths as they climb up tree trunks preventing them from laying eggs. No eggs means no caterpillars.

Sticky bands are made by wrapping duct tape or similar products around trees and covering it with a sticky compound that traps the insects.  These bands have been used to reduce defoliation by other caterpillars such as gypsy moth and winter moth that also have climbing adults or larvae. Hopefully they will work just as well for cankerworms and provide a non-toxic solution for homeowners and municipalities to manage this pest.

Many tree pests are more abundant in the hottest parts of urban landscapes. Our lab, in collaboration with the Dunn Lab, has been studying scale insects in Raleigh, Baltimore, New York, and Boston. We have found consistent evidence that scale insects and other pests flourish on trees in hot sites but are absent just blocks away in cooler sites.

A goal of the cankerworm project is to determine how temperature affects their abundance and seasonal activity. This will help us predict which trees are most at risk for cankerworm and other pest infestations. It also helps us predict how pests might respond to global warming. If pest outbreaks occur in the hottest parts of cities, why wouldn’t such outbreaks occur in forests if the forests become warmer due to global climate change?