Box tree moth

Features - Pest Control

The industry must stay vigilant to keep this destructive pest out of the United States.

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Box tree moth caterpillars are about a 1/2-inch long, dark green on top with dark stripes down the sides of the body.

The box tree moth, Cydalima perspectalis, is native to China, Korea and Japan, and was discovered in Europe in 2007. The insect has spread profusely and is now present in over 30 countries. How did this insect get to Europe from China? It has been suggested that the movement of infested boxwood plants from China through the nursery trade may be responsible for the introduction of the box tree moth into Europe. In 2018, the box tree moth was detected in Ontario, Canada, which is the first detection of this insect in North America. Again, the movement of infested boxwood plants may be how the insect arrived in North America.

The box tree moth is known to feed exclusively on boxwoods, but the insect will feed on many boxwood species and cultivars. Therefore, because boxwoods are widely grown in nurseries and incorporated into landscapes throughout the United States, the potential economic impact of this insect could be substantial.

During a trip to the Netherlands in May 2019, I was able to observe, first-hand, the destructive nature of this insect pest feeding on the common boxwood, Buxus sempervirens. It was striking the extent of the damage in localized areas—with complete defoliation. Consequently, due to the potential for the box tree moth to ruin the aesthetic value of boxwoods in landscapes; people may start using plastic boxwoods.

Box tree moth caterpillars will feed on leaves and bark of boxwood.
Box tree moth caterpillars can completely defoliate boxwood.

Biology and damage

Mature larvae are about a 1/2-inch long, dark green on top, with dark stripes that extend down the sides of the body. The larvae have black heads, hairs protruding from the sides of the body and two black spots on each abdominal segment. They may be difficult to see because they hide during the day within the plant canopy. Young larvae feed on the lower leaf surfaces whereas older larvae feed inside loose strands of webbing and skeletonized leaves with only the mid-ribs remaining, which causes leaves to turn brown. The extensive webbing is generally filled with frass and cast skins and is very apparent on infested plants.

In addition to feeding on leaves, larvae will also feed on the bark, which can kill a boxwood plant. The larvae undergo five to seven instars and then pupate within the canopy of a boxwood plant. Adult moths emerge from pupae and live approximately two weeks. Box tree moth overwinters as a larva in a cocoon between leaves that are tightly bound by silk. There may be two to four generations per year in Europe.

The extensive webbing is generally filled with frass and cast skins and is very apparent on infested plants.

Management

There are no known natural enemies (e.g. parasitoids and predators), and even birds and animals will not feed on box tree moth caterpillars because they harbor an alkaloid toxin that protects them from predation.

Insecticides such as pyrethroids, spinosad, chlorantraniliprole and Bacillus thuringiensis subsp. kurstaki may be effective against the box tree moth. However, timing of application is important, as well as thorough coverage of all plant parts. Physical removal by hand picking the larvae has been suggested as an option to reduce damage from the box tree moth; however, this can be time consuming and expensive.

It is important that we do the best we can, from a regulatory standpoint, to prevent the box tree moth from entering the United States. If not, then we will be dealing with another invasive insect pest on a plant that is extensively grown in nurseries and planted in landscapes throughout North America.

About the author: Raymond A. Cloyd is a professor and extension specialist in Horticultural Entomology/Plant Protection with the Department of Entomology at Kansas State University. rcloyd@ksu.edu