A new ambrosia beetle, Xylosandrus crassiusculus, detected in Italy: addition to the EPPO Alert List
Dr Minuto (CERSAA, IT) attracted the attention of the EPPO Secretariat to the first record of an Asian ambrosia beetle, Xylosandrus crassiusculus (Coleoptera: Scolytidae) in Italy and in Europe. The insect was first trapped in Toscana (near Pisa) in a mixed forest dominated by Pinus pinaster and Quercus cerris (Pennacchio et al., 2003). As no recent information has been published, it is not known whether the pest has been able to establish in Toscana and which tree species were attacked. In 2007 and 2008, damage caused by X. crassiusculus was observed on Ceratonia siliqua (carob tree) in private and public gardens in Alassio (Liguria). The extent of the infestation of the pest in Liguria is not known. Because X. crassiusculus is a very polyphagous pest of woody plants and has the potential to cause damage in areas where it has been introduced (i.e. in the USA), the EPPO Secretariat decided to add it to the Alert List.
Xylosandrus crassiusculus (Coleoptera: Scolytidae – Asian ambrosia beetle, granulate ambrosia beetle)
Why: Xylosandrus crassiusculus is a highly polyphagous pest of woody plants which has recently been reported from Italy. It originates from Asia and has been introduced to other parts of the world, most probably with trade of plants and wood. In particular, it has been introduced into the USA in the 1970s where it has become a pest of fruit tree orchards and ornamental tree nurseries. As this pest might present a risk to many woody plants in nurseries, plantations, orchards, parks and gardens, the EPPO Secretariat decided to add it to the EPPO Alert List.
Where: It is considered that X. crassiusculus originates from Asia, and that it was introduced into Africa hundreds of years ago by early traders. More recently, it has been introduced into the Americas (detected in the USA in the 1970s; in Costa Rica and Panama in the 1990s).
EPPO region: Italy (Liguria, Toscana). For the moment, it is not known whether the pest is established or not.
Asia: Bhutan, China (Fujian, Hong Kong, Hunan, Sichuan, Xizhang, Yunnan), India (Andaman and Nicobar Islands, Assam, Himachal Pradesh, Karnataka, Madhya Pradesh, Maharashtra, Tamil Nadu, Uttar Pradesh, West Bengal), Indonesia (Irian Jaya, Java, Kalimantan, Maluku, Nusa Tenggara, Sulawesi, Sumatra), Japan (Hokkaido, Honshu (including Ogasawara Islands), Kyushu, Shikoku), Korea Democratic Peoples’ Republic, Korea Republic, Malaysia (Sabah, Sarawak, West Malaysia), Myanmar, Nepal, Pakistan, Philippines, Sri Lanka, Taiwan, Thailand, Vietnam.
Africa: Cameroon, Congo Democratic Republic, Côte d’Ivoire, Equatorial Guinea, Ghana, Kenya, Madagascar, Mauritania, Mauritius, Nigeria, Seychelles, Sierra Leone, Tanzania.
North America: USA (Alabama, Arkansas, Delaware, Florida, Georgia, Hawaii, Indiana, Louisiana, Maryland, Mississippi, New Jersey, North Carolina, Ohio, Oklahoma, Oregon, South Carolina, Tennessee, Texas, Virginia, Washington). X. crassiusculus was first recorded in May 1974 in South Carolina on a dying graft of Liquidambar styraciflua. It is now well established in South-Eastern USA.
Central America: Costa Rica, Panama. In these countries where it is now considered established, X. crassiusculus has been found in primary tropical forests on many tree species. However, in these natural forests, it is not known if it can kill healthy trees.
Oceania: New Caledonia, Palau, Papua New Guinea, Samoa.
On which plants: X. crassiusculus is a highly polyphagous pest which can feed on many tree and shrub species (only Coniferae are apparently not attacked by this pest). In tropical areas, it has been reported on economically important crops (e.g. Camellia sinensis, Carica papaya, Cocus nucifera, Coffea arabica, Mangifera indica, Theobroma cacao) or forest tree species (e.g. Aucoumea kleineana, Tectona grandis). In more temperate areas, it has been reported on many fruit and nut crops (e.g. Carya illinoinensis (pecan), Ceratonia siliqua (carob), Diospyros kaki, Ficus carica (fig), Malus domestica (apple), Prunus avium (cherry), P. domestica (plum), P. persica (peach)); as well as on many forest and ornamental woody species (e.g. Acacia, Alnus, Azalea, Cornus, Eucalyptus, Hibiscus, Koelreuteria, Lagerstroemia, Liquidambar, Magnolia, Prunus, Quercus, Populus, Salix, Ulmus).
Damage: Adults and larvae bore into twigs, branches or small trunks of woody host plants and introduce a symbiotic ambrosia fungus (Ambrosiella sp.) on which they feed. The insect usually bores galleries within stems of a rather small diameter (2.5-8 cm) but larger logs can be attacked (e.g. up to 30 cm diameter).Unlike other ambrosia beetles which normally attack only stressed or damaged plants, X. crassiusculus is apparently able to attack healthy plants. Infested plants can show wilting, branch dieback, shoot breakage and general decline. Newly planted seedlings are often attacked at the root collar and the resulting girdling can stunt or kill the young tree. When boring galleries, frass is pushed out in the form of a compact cylinder which may reach 3 to 4 cm long before it breaks off (resembling a ‘toothpick’). On Prunus species, abundant gummosis is also produced. In the USA, it is considered that X. crassiusculus has become an important pest of ornamental and fruit trees, more particularly in nurseries and trees used in landscaping. Although no figures are given, it is stated that X. crassiusculus has caused moderate to heavy losses in US nurseries (e.g. on potted Quercus shumardii and Ulmus parviflora), on chestnut, peach and pecan orchards. In other parts of the world, tree mortality has been reported on Mangifera indica in Pakistan, Aucoumea klaineana and Khaya ivorensis plantations in Ghana.
Adults are small dark reddish brown scolytids (female: 2-3 mm long, males: 1.5 mm). Larvae are white, legless, C-shaped with a well developed capsule, and cannot be easily distinguished from other scolytids. Populations essentially contain females (1:10 male-female ratio). Adult males do not fly and remain inside the galleries. X. crassiusculus is an inbreeding species (females mate with their brothers). When females emerge, they leave infested plants and fly to new hosts. They start to bore a tunnel (round entrance hole of 2 mm diameter) with a brood chamber and one or more branches into the sapwood (and sometimes the heartwood). Eggs are laid in the brood chamber. Larvae hatch and feed on the symbiotic fungus growing inside the galleries. In the tropics, breeding is continuous throughout the year with overlapping generations. In South-Eastern USA, beetles are active from March to the autumn, and the life cycle takes about 55 days, with usually two generations per year.
Pictures can be viewed on the Internet:
Dissemination: Flight of adult females is the main means of movement and dispersal to new plant and new areas over short distances. The is no data on the distances they can fly but data obtained from flight traps in Panama suggested that X. crassiusculus normally flies at heights under 10 m above the ground. Over long distances, trade of infested plants, wood, and packing wood material can transport X. crassiusculus.
Pathway: Plants for planting, cut branches, wood, packing wood material from countries where X. crassiusculus occurs.
Possible risks: Many woody plants attacked by X. crassiusculus are important fruit crops, forest trees or woody ornamentals in the EPPO region. Although Scolytine beetles are usually considered as secondary pests in their native forests, it seems that X. crassiusculus can occasionally become a significant and aggressive pest in its introduced range. Although data is lacking on its economic impact, it seems that it has the potential to be a pest in nurseries, orchards and plantations. Data is lacking on its potential impact in forests and wood production. Pest control and detection is difficult due to its concealed mode of life. In the USA, it is recommended to removed and destroy infested plants. Repeated insecticide treatments may help to reduce pest populations. Lindgren funnel traps baited with ethanol lures can be used to monitor flight periods and evaluate the importance of pest populations. In New Zealand, X. crassiusculus is included in the ‘List of regulated pests potentially associated with woodware’. Considering the areas where X. crassiusculus has been introduced and the damage it may cause, it seems that this species has the potential to establish and cause damage to a large number woody plants in Europe, cultivated for fruit production, forest and ornamental purposes.
EPPO RS 2009/053
Panel review date: -
Entry date 2009-03
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Personal communication with Dr Andea Minuto, CERSAA, Albenga (IT), 2008-10.