Last week we had two papers published about cankerworms. Cankerworms are caterpillars that defoliate oaks and other tree species. Cankerworms outbreaks have
Cankerworm larva. Photo: SD Frank
become increasingly common in urban areas like Charlotte, Durham, and Raleigh. Damage can be extensive. Many trees on 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. More about cankerworms here.
The first paper, published in Arboriculture and Urban Forestry, is “The effect of sticky bands on cankerworm abundance and defoliation in urban trees“ by Bobby
Chanthammavong who has worked in my lab for almost two years. He conducted this research as an undergraduate during the cankerworm outbreak last year. He wanted to test the efficacy of sticky bands, a non-insecticide management tactic, to help reduce cankerworm damage to campus trees. Sticky bands exploit an unusual aspect of cankerworm biology: the females moths are wingless. Therefore they have to climb up trees to lay eggs. Sticky bands are wrapped around trees to capture the moths as they climb. If they never reach the canopy to lay eggs then you shouldn’t have cankerworms or damage come spring.
Sticky bands worked fairly well and reduced cankerworm abundance in the trees but did
Maple partially defoliated by cankerworms. Photo: SD Frank
not reduce overall defoliation. Lots of cities including Charlotte and Durham, NC use sticky bands each year on hundreds or thousands of trees. 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. Bobby was supported in part by an NCSU Undergraduate Research Grant. His work appeared in the Bulletin and Technician.
The second paper “Bad neighbors: urban habitats increase cankerworm damage to non-host understory plants” in Urban Ecosystems tests the hypothesis that cankerworm damage to plants is greater in urban settings than in forests. Cankerworms often drop from host trees and land on understory plants or the ground. We found that in urban settings where plant communities and habitat were simple (just shrubs and mulch in landscape beds) the shrubs below cankerworm infested trees were
Native dogwood damaged by cankerworms in an urban landscape. Photo: SD Frank
defoliated more than the same species of shrubs in forests where plant communities were more complex (shrubs, ground cover, leaf litter, etc). There is a caveat though: cankerworms damage native plant species more than exotic, ornamental species. As cankerworm outbreaks become more frequent and severe in urban areas they will damage more than just their primary hosts but damage may be reduced by diversifying the plants and structure of urban landscapes. This work was funded in part by the Southeast Climate Science Center.
These papers address our goals of understanding the ecology of urban ecosystems, why pest damage is often more severe in urban landscapes, and developing management tools to protect urban trees.