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Resin bleeds from oviposition holes and larval tunnels in the bark. Larval activity is recognized by the presence of galleries under the bark and, later, tunnels in the wood. Masses of wood shavings extruding from round exit holes are also signs that adults have emerged from infested wood. Piles of wood shavings also collect at the base of infested trees.
In China, control measures include the direct application of insecticides (Chen et al., 1990; Liang et al., 1997), trap trees combined with insecticide treatments (Sun et al., 1990) or the use of insect-pathogenic nematodes (providing up to 94% mortality; Liu et al., 1992). As certain poplar hybrids are relatively resistant (Qin et al., 1996), the planting of such hybrids is now preferred, and the use of very susceptible hybrids is avoided. Control strategies in China have recently been reviewed by Luo et al. (2003).
In the USA (Haack, 2003; Lance, 2003), control measures aim to contain and eradicate the outbreaks in urban areas. However, the cryptic life style and tendency of the beetle to lay small numbers of eggs on several trees combine to make it difficult to define the limits of the outbreak and thus eradicate the beetle without destroying large numbers of trees. In most situations, wholesale felling of infested trees is unlikely to be a viable option, unless the infestation is very localized.
In the USA and in Europe, strong measures have been taken for wood packing materials from China. This includes packing cases and dunnage. Unger (2003) has reviewed the measures needed to exclude the pest from Germany. The case of A. glabripennis has been the main stimulus for the development by the FAO Interim Commission on Phytosanitary Measures of an international standard 'Guidelines for regulating wood packaging material in international trade' (ICPM, 2002). Such packaging should be treated by methods recognized to have adequate efficacy against all wood pests. These currently include heat treatment (to an internal temperature of 56°C for 30 min). Once treated, packing wood is unlikely to be re-infested, so such wood (especially crates and pallets) can continue to be used in trade. An internationally recognized mark is stamped to the treated wood. The international standard was approved in 2002 and is now progressively being implemented worldwide.
Over the past 30-40 years (i.e. since the 1960s), there has been a policy in China to plant hybrid poplars in plantations, along roads, around farm buildings, etc. This started in Henan and Shandong provinces, but was eventually applied in most of the country. Initially, rather few hybrids were used, on a vast scale. Some of these hybrids were imported from other continents, whereas others were bred in China. Certain of them, but not all, proved to be very susceptible to A. glabripennis and suffered serious damage. A. glabripennis has proliferated on these susceptible hosts, becoming a common pest in many parts of China, also attacking a range of other hardwood hosts, especially Salix spp. These hosts appear to be mainly fruit, ornamental and amenity trees. Since the 1980s, hybrids resistant to the pest have been used for new plantations of poplar, and there has been a corresponding decline in the importance of A. glabripennis. There is no indication that A. glabripennis is a pest of natural forests in China. Recently (Taketani, 2001), a project to plant a vast forest shelter belt (the 'Great Green Wall') across north-west China to protect from incoming sandstorms is said to be threatened by A. glabripennis.
Poplar wood damaged by A. glabripennis larvae can be downgraded and lose value by up to 46% (Gao et al., 1993). Severe damage is caused between 21° and 43°N and 100° and 127°E in China (Yan, 1985). The boring larvae damage the phloem and xylem vessels, resulting in heavy sap flow from wounds which are then liable to attack by secondary pests and infection. Infested trees lose turgor pressure, and leaves become yellow and droop. Structural weakening of trees by the larvae in urban regions poses a danger to pedestrians and vehicles from falling branches. The adults can also cause damage by feeding on leaves, petioles and bark. Damage to the fruiting shoots of fruit trees results in particular economic loss.
In the USA, suppressing a 1996 infestation in New York State cost more than 4 million USD (USDA, 1998). Nowak et al. (2001) have estimated that the maximum potential national urban impact of A. glabripennis would be a loss of 34.9% of total canopy cover, 30.3% tree mortality (1.2 billion trees) and value loss of 669 billion USD.