Editor’s note: This is a guest post by Steve Frank, an entomology researcher at NC State.
If you live in the eastern United States, you may recently have noticed a ton of caterpillars hanging from trees on fine silk threads. Maybe you picked caterpillars off co-workers or family members when they came in from outdoors. These were fall cankerworms and they are increasingly common and damaging in urban areas like Charlotte, Durham, and Raleigh.
Cankerworms are green or brown caterpillars that feed on many deciduous tree species. Oaks and maples are particular favorites. Adult cankerworm moths lay eggs in host trees during winter. The eggs hatch when new leaves are just developing on trees. In years when cankerworms are abundant they can eat every leaf off large trees.
In recent years, many trees on NC State’s campus were completely defoliated. In Charlotte we have seen entire neighborhoods defoliated. Trees can only tolerate two or three consecutive years of defoliation before their growth declines or they die. Cankerworms often drop from host trees on threads to escape predation or to seek new food. Thus, they frequently damage plants growing next to or below their host trees. (An overview of recent NC State research on cankerworms in urban environments can be found here.)
Earlier this month my lab published a paper in Arboriculture and Urban Forestry, titled “The effect of sticky bands on cankerworm abundance and defoliation in urban trees.” Chanthammavong “Bobby” Noukoun, who has worked in my lab for almost two years, is first author. He conducted this research as an undergraduate during the cankerworm outbreak in 2013. He wanted to test the efficacy of sticky bands, a non-insecticide management tactic, to help reduce cankerworm damage to campus trees.
Sticky bands are bands of tape or plastic that are wrapped around tree trunks and covered with a sticky product called Tanglefoot. Sticky bands exploit an unusual aspect of cankerworm biology: the female moths are wingless. Therefore they have to climb up trees to lay eggs and can get stuck in sticky bands before they reach the canopy. If moths never reach the canopy to lay eggs then you shouldn’t have cankerworms or damage come spring.
Bobby installed zero, one, or two sticky bands on 36 campus willow oak trees, then measured caterpillar abundance and defoliation in tree canopies. The sticky bands caught over 16,000 female cankerworm moths, which can each lay over 100 eggs. Sticky bands reduced cankerworm abundance in the trees but did not measurably reduce defoliation. However, defoliation of most study trees was less than 30 percent (far from total defoliation). Many cities install sticky bands on hundreds or thousands of trees each spring to protect them from defoliation. Since the tiny caterpillars can float from tree to tree (entomologists call it ballooning), banding at a large scale probably works better than banding only a few of the trees in an area.
We are going to follow up this work with research to investigate the efficacy of sticky bands at the scale of entire neighborhoods. Bobby was supported in part by an NC State Undergraduate Research Grant.