Cydalima perspectalis (Walker) – (Box tree moth) – Fact sheet
Native to Asia, Cydalima perspectalis (Walker), box tree moth, is an invasive pest currently causing severe damage to boxwood, Buxus spp., in Europe. It was detected in Germany and the Netherlands around 2006 and is believed to have arrived in Europe with a shipment of Buxus plants from Asia.
Since arriving, it has continued to spread into new areas and is now found in up to 30 European countries. This spread has been aided by the free market for live plants in the European Union and by the fact that there are two species of boxwood, B. sempervirens and B. balearica that are native to Europe, and are found in the natural environment.
Boxwoods are planted as ornamentals and typically used for edging, as hedges, and/or clipped into different shapes to make topiaries (Figure 1). However when infested, the plants are disfigured by the loss of leaves, by webbing spun by the larvae, as well as larval excrements (Figure 2). Larvae feed principally on leaves of the host but may also attack the bark.
Box tree moth was detected in Toronto in August 2018 by a citizen scientist as reported in an online publication (see iNaturalist.org's Blog). In November 2018, the Canadian Food Inspection Agency (CFIA) confirmed the presence of box tree moth in an urban neighbourhood in Toronto. This is the first confirmed report of this pest in North America.
Cydalima perspectalis is primarily a pest of Buxus plant species (Family Buxaceae). In Europe, Buxus spp. recorded as hosts of this moth are:
- Buxus balearica (Balearic boxwood)
- Buxus bodinieri
- Buxus harlandii (Harland boxwood)
- Buxus megistophylla
- Buxus microphylla (Little-leaf box)
- Buxus rugulosa
- Buxus sempervirens (Common boxwood)
- Buxus sinica (Chinese box)
In Asia, C. perspectalis is also a pest of Buxus spp. However, plant species other than Buxus have also been recorded as hosts. The plant species listed below are hosts of C. perspectalis in Asia in addition to the species listed above:
- Euonymus alata (Winged spindle) and E. japonicus (Japanese spindle tree) – (Family Celastraceae)
- Ilex purpurea (Purple-leaved holly) – (Family Aquifoliaceae)
- Murraya paniculata (Orange jasmine) – (Family Rutaceae)
One species of boxwood, B. vahlii, is native to North America. A small population is found in Puerto Rico and the United States Virgin Islands. There are no native boxwoods in Canada. Currently, Canadian nurseries source most of their boxwoods from domestic stocks or import them from the US. Boxwoods were originally brought to North America as nursery stock from Europe and Asia, bred, and sold to homeowners. Thus, they are found in urban areas only, planted around houses and in small gardens. There are no natural stands of boxwood in Canada unlike the situation in Europe.
Asia: China, India, Iran, Japan, South Korea.
Europe: Austria, Belgium, Bosnia-Hercegovina, Bulgaria, Croatia, Czech Republic, Denmark, France, Georgia, Germany, Greece, Hungary, Ireland, Italy, Liechtenstein, Luxembourg, Montenegro, Netherlands, Poland, Romania, Russia, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey, United Kingdom, Ukraine.
Canada: Box tree moth was detected in an urban neighbourhood in Toronto, Ontario, in August 2018. The source of this introduction is unknown.
Geographical location, larval food source, as well as temperature have significant impacts on the biology of C. perspectalis with respect to adult longevity and fecundity, larval developmental time, diapause, number of generations in a year, etc. Adult moths live about 14 days and are good flyers, with the potential to disperse 7-10 km per year. During the day, they can be found resting on host plants or on other surrounding plants.
Eggs are laid on the underside of host leaves, usually in a cluster of about 10-20 eggs. The eggs hatch after about 3 days and young larvae feed on the underside of the leaves, webbing the leaves, one of the most obvious signs of an infestation. Depending on temperature and larval food source, there may be up to 7 larval instars. It takes about 14 days for the larvae to mature and pupate. Pupae live about 14 days before becoming adults.
Cydalima perspectalis has 1 to 5 generations a year depending on geographical location. There is an obligatory diapause of 6 to 8 weeks induced by a day length of about 13.5 h, but may vary depending on the geographic location and the development temperature. Cold stress during diapause is not a critical factor for larval survival because C. perspectalis can survive in areas where the minimum winter temperature is about -30°C. It overwinters in the larval stage in a silken cocoon spun between host leaves. The overwintering stage varies from the second to fifth instars, depending on geographical location. In central Europe, it is the third instar that overwinters. Temperature threshold for the development of eggs, larvae, and pupae vary between 8°C and 12°C.
Detection and identification
Damage to boxwood plants is caused by the larvae feeding primarily on leaves and sometimes on the bark. Infested plants are disfigured by the loss of leaves and by the webbing spun by the larvae. Younger larvae feed by eating the lower surfaces of the leaves only, leaving the upper epidermis intact. Older larvae feed inside the webbing and skeletonize the leaves, leaving only the midribs, and occasionally the outer margin intact. Presence of webbing, frass (excrement), and moulted black head capsules may also be apparent in and around infested plants. The defoliation and dieback are unsightly, and reduce the value of the plants.
Eggs, which are laid in clusters, are greenish yellow in colour when first laid (Figure 3). Black dots start to show as the larval head capsule is forming. Eggs hatch in about 3 days.
On hatching, larvae are greenish yellow in colour with a shiny black head. As they mature, they become more greenish and develop a striking pattern of thick black and thin white stripes along the length of the body (Figure 4). Mature larvae may be up to 4 cm long.
Mature larvae pupate in a cocoon of white webbing spun among the leaves and twigs of the host. Pupae are on average 1.5 to 2.0 cm long. They are always hidden and rarely visible in the field (Figure 5).
Adults are described as medium-sized moths with a wing span of about 4 cm. Two colour variants have been recognized. The more common variant has white coloured wings with thick dark brown border trimmings. The ‘melanic' variant is less common and has brown wings with small white streak on the forewing (Figure 6).
Prevention and control
At this time, raising public awareness on the risk of moving infested boxwood material is essential to help control and limit the spread of C. perspectalis in Canada. Boxwood plants can be infested with all life stages of the box tree moth. In Europe, chemical treatments and biopesticides are available for use on boxwood; however many of these compounds may not currently be registered for use on boxwood or available in Canada.
To help determine the extent of its distribution, the CFIA is encouraging all stakeholders to submit samples of any pests they observe on boxwood plants to their local CFIA office. Suspect sightings can also be reported online. This information will assist in evaluating the threat and will help direct the next steps for Canada.
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