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The Box Tree Moth (Cydalima perspectalis)

The Box Tree Moth (Cydalima perspectalis). Photo: SINP Archives

The Box Tree Moth (Cydalima perspectalis). Photo: SINP Archives

If you have noticed that yours Boxwood (Buxus sempervirens) is losing leafs and is covered in webbing, there is great probability that it was attacked by the Box Tree Moth. This invasive alien species originates from Asia (China, Japan and Korea) and in Europe it was first recorded in Germany in 2006. The Box Tree Moth was probably imported with the Boxwood plants from China and has rapidly spread throughout Europe, and recently is recorded in 18 European countries. It causes heavy defoliation and consequently dying of the plants. Main dispersal path is via trade of infected plant materials since the Boxwood is one of the most popular ornamental plants but it also spreads by flying of adult moths. Since the Boxwood is a very frequent plant in Croatian private and public gardens and parks, the Box Tree Moth could completely destroy visual identity of historic parks, which have been there for centuries.

The Boxwood attacked by the Box Tree Moth (Cydalima perspectalis). Photo: SINP Archives

The Boxwood attacked by the Box Tree Moth (Cydalima perspectalis). Photo: SINP Archives

In Croatia, the Box Tree Moth was first registered 2012 in Istria. During the next two yeras it was spread throughout whole country from the northern to the southern border (observations of Dinka Matošević, dr.sc. from Croatian Forest Research Institute).

The Box Tree Moth (Cydalima perspectalis) is a moth from the family Crambidae. It feeds on leaves of Buxus spp. (B. sempervirens, B. microphylla, B. sinica and B. colchica), Ilex purpurea, Euonymus japonicus, Pachysandra terminalis and Murraya paniculata. The caterpillars are very voracious. During its development one caterpillar can eat up to 45 leaves and more than hundred caterpillars could feed on a single bush! The Box Tree Moth can easily be identified by the complete Boxwood defoliation as well as silk threads on the bush. It overwinters as juvenile cocooned larva so it starts to feed on leaves in the early spring (from March) which continues till October. During one season there are two or three generations with adults. The wingspan of an adult form is 4 cm.

The adult moth of Cydalima perspectalis. Source: Wikipedia

The adult moth of Cydalima perspectalis. Source: Wikipedia

There are no efficient control methods for the Box Tree Moth. Ecologically, the most acceptable method is mechanical removal of sprouts in which caterpillars hibernate over the winter, as well as the caterpillars and pupae. It is recommended to collect and burn them in order to prevent the development of a new generation in the spring and minimize the damage. If the infected Boxwood plants are trimmed, the plant material should be burned rather than composted to prevent further spread of infection. “Washing” the shrubs with pressure cleaner is proven to be a very efficient removal method but it is a short-term solution. Chemically, the Box Tree Moths can be insecticide-treated. It is advised to cover and wrap the plants a day or two after using insecticides to destroy as many caterpillars as possible. All these methods effectively reduce number of caterpillars, but unfortunately if there are infected plants in the neighborhood; it is almost certain that uninfected plants will be infected again.