Box tree moth
The moth of the boxwood borer reaches a wingspan of 25-30 mm and shows a very characteristic wing pattern. The forewings are colored white and have a broad black-brown band on the anterior margin and border. In the center field a small brown bulge and a crescent-shaped white spot is visible. The white hind wings also have a brown fringe. There are also completely brown colored moths with a white spot.
The caterpillars grow up to 5 cm long, are yellow-green in color and have black and white longitudinal stripes, black spots, white bristles and a black head capsule.
The boxwood borer Cydalima perspectalis (synonym: Diaphania perspectalis) belongs to the weevil family (Crambidae).
The moths fly from June and lay their shield-shaped yellowish eggs in small groups on the undersides of leaves. The hatching caterpillars live in loose webs and pass through six larval stages, finally reaching a size of up to 5 cm. They pupate in a cocoon on their host plants. After a short period of dormancy, a finished moth hatches from the cocoon. The boxwood borer goes through its development cycle three times in each year - one speaks of three generations.
Hibernation takes place as a caterpillar in a web on the host plants. After overwintering, the caterpillars begin feeding from mid-March to early April.
The caterpillars live in loose webs and feed on leaves - initially they cause a scraping feeding on the leaves in the inner or lower part of the plant, which is why they are often overlooked at the beginning of the season. They are capable of completely defoliating their host plant, causing it to die. When food is scarce, they then also feed on the green parts of the bark.
The caterpillars' droppings, which collect in the webs and on the leaves, are also conspicuous.
The boxwood borer originates from Japan and was first discovered in Europe in 2007 in Germany. From there, it has spread steadily. In Austria, the first occurrence of the boxwood borer was reported in Vorarlberg in 2009. Later, it was also found in Styria and Lower Austria. The pest is now widespread throughout Austria.
Prevention and control
- No purchase/exposure of already infested young plants
- Do not move infested plants to areas free of infestation
- Take special care in the vicinity of cemeteries, where experience has shown that infested plants are often abandoned.
- Regular infestation checks of the inner and lower areas of the box trees from March to October
- Checking of the moth flight by means of pheromone traps
- Mechanical cutting out of the webs and collection of the larvae with subsequent destruction
- Pruning of infested box trees preferably after the moth has laid its eggs
- Planting of replacement plants such as barberry(Berberis spp.), holly(Ilex spp.) or honeysuckle(Lonicera spp.)
- Spray treatment with an approved agent for the control of biting pests and free-feeding butterfly caterpillars in ornamental horticulture (see list of plant protection products approved in Austria).
- The beneficial bacterium Bacillus thuringiensis subsp. kurstaki can be used as a biological plant protection agent against young caterpillars
- Apply spray broth under high pressure (blower sprayer) and wet all plant parts well
- Encourage natural enemies (e.g. birds). No parasites have been found on boxwood borers to date. Since they store the toxins of the boxwood in their bodies, they are also toxic or unattractive to potential predators. However, native songbirds (such as sparrows, titmice, ...) have already been observed feeding their young with box elder caterpillars.
Last updated: 17.11.2021