Box tree caterpillar

Box tree caterpillar Cydalima perspectalis (syn. Diaphania perspectalis)

The boxwood moth (Cydalima perspectalis) is a species from the grass moth family (Crambidae) which was first described by Francis Walker in 1859. This species occurs naturally in East Asia and is an invasive exotic in Europe, first observed on the border Germany/Switzerland in 2006.

Description

The wings of the boxwood moth are white with a dark edge and have a wingspan of about 4 cm. There is also a rare, all-brown version. Young caterpillars are yellowish and only a few millimetres in size but they quickly grow into bright green specimens with a black head. They can grow up to 4 cm long and are then almost a month old. After the caterpillar stage they pupate in the left behind web for a period of about 14 days. The butterflies have a short lifespan of about 8 days but each moth can lay as much as 500 eggs. In Belgium and the Netherlands 2 generations occur. This exotic hibernates as a spun-in caterpillar between the boxwood plants.

Prevention

The boxwood moth is found in East Asia (Japan, South Korea, China) and was introduced in Europe in 2006 via natural stone packaging wood from Asia, according to a study by the University of Basel. Afterwards, the distribution went quickly from Germany/Switzerland to the rest of Europe. The first reports in the Netherlands date from 2007, but at that time they were still very local. Due to the invasive nature of this species, in 2018 the whole of Europe is infected with this alien moth.Since we're dealing with an invasive exotic, alertness is certainly an issue. In the country of origin boxwood as well as other plants are affected. In Europe the boxwood moth seems to have a predilection for our native Buxus sempervirens, which does not occur in Asia. Other plants could also be affected.

Damage

The young caterpillars eat parts of the foliage but it is mainly the older caterpillars that cause a lot of damage. Adult caterpillars can defoliate an entire plant in a short time. Only spider mites remain on the affected plants. Although the plant looks desolate at that moment, the boxwood will sprout fresh green again after 8 weeks, due to its strong recuperation capacity. However, it is important not to let the plant get eaten again. There are 2 periods with a lot of eating: April and July.

Control

The caterpillars of the boxwood moth are easy to control both chemically and biologically. Products based on spinosad (Conserve Garden), permitted in organic farming, have a long persistence and appear to be as efficient as chemical agents. Products based on Bacillus thuriengensis (not permitted for private individuals in Belgium and the Netherlands, but it is in the rest of Europe) work especially well on young caterpillars. Chemical agents based on lambda-cyhalothrin (Karate Garden) or deltamethrin (Decis) also work well. Professional garden contractors, holders of a phytolic license, have a broader range of products.

Important infromation

  • Treatment at an early stage results in much less damage. Follow our warning messages.

  • Preferably treat your plants with biological agents.

  • Eaten plants will recuperate and do not need to be removed.

  • Pheromone traps can be used for monitoring. They are useless for control purposes because only a small proportion of the males are caught.

  • Natural enemies are beginning to discover this invasive exotic and birds in particular love the caterpillars. The caterpillars themselves are poisonous (buxine) but birds don't seem to be bothered by this. Bird mortality as a result of treatment with crop protection has not been proven and the summary research conducted on this subject does not show that caterpillars are adversely affected.