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Attacked trees have delayed growth. Whole trees or part of trees start to wilt and often perish within a short time (especially young fruit trees).
In April/May small, round entry holes (about 2 mm in diameter) become visible in the bark of trunks and larger branches. Fine, white frass trickles out from such holes. In plants still in good health, plant sap or gum (especially in Prunus) flows out of the holes.
In general, X. dispar attacks only stressed trees which are already damaged by frost, drought, wetness, transplanting, root feeders or diseases. The beetle may also attack trees before conspicuous external evidence appears to indicate the stressed condition of the tree. Attacks by X. dispar may be regarded as symptomatic of an altered physiological condition in the tree. However, Vasseur and Schvester (1948), Schvester (1954), Egger (1973), Postner (1974), Viggiani (1979), Schröder (1996) and Perny (1998) report that apparently healthy trees, especially apple, pear, apricot and hazel, may also be attacked. This occurs mainly when insect populations are high.
In most areas, X. dispar is considered to be a secondary pest (Schneider-Orelli, 1913; Linsley and MacLeod, 1942; Balachowsky, 1963; Postner, 1974; Zöggeler, 1987; Schick and Thines, 1988; Juillard-Condat and Perrau, 1989; Keimer, 1990; Mani et al., 1990, 1992; Schröder, 1996; but compare Bhagwandin, 1993; Perny, 1998; Kühnholz et al., 2003). Weakened trees are especially attractive to this beetle.
For this reason all cultural measures improving the health of trees must have priority. New plantations are at risk, particularly during the first and the second spring after planting. Avoid drying of roots before and after planting. Remove and destroy infected trees and branches immediately when attack is observed, or at the latest before the beetles of the new generation leave the galleries the following spring.
No method of biological control of X. dispar exists at present. The natural enemies listed do not provide effective control, and augmentation is not likely to produce much improvement. Canganella et al. (1994) suggest that the bacteria (Pseudomonas chlororaphis and Bacillus subtilis) they found on the insect and in the galleries may represent the starting point for future research.
Schvester (1954) observed that attacked trees often produce an odour of alcohol. He explained this by the interruption or slowing down of plant sap transport and by the fermentation of this sap. Roling and Kearby (1975) showed that oak trees injected with ethanol attracted ambrosia beetles. Ethanol is apparently a good signal for a suitable host plant, especially for an ambrosia beetle cultivating a fungus in wet plant tissue (Klimetzek et al., 1986). All these observations may explain why many ambrosia beetles are attracted by alcohol traps.
In forests, window flight traps baited with ethanol are used, often in combination with pheromones, to estimate the flight periods and flight pattern of bark and ambrosia beetles (Moeck, 1970; Roling and Kearby, 1975; Annila, 1977; Schroeder and Lindelöw, 1989; Markalas and Kalapanida, 1997).
The red wing trap, baited with ethanol (Rebell rosso), has been developed in Switzerland to attract X. dispar in orchards and vineyards. It has proved to be useful in monitoring and in control systems (Mani et al., 1986, 1988, 1990, 1992). This method has become accepted in several countries (Zöggeler, 1987; Juillard-Condat and Perrau, 1989; Schröder, 1996; Lagowska and Winiarska, 1997). For other designs of trap using ethanol as a bait, see, for example, Bambara et al. (2002), Oliver and Mannion (2001) and Grégoire et al. (2003).
For monitoring, one or two traps per hectare of orchard or vineyard have to be placed in spring, when maximum temperatures rise above 17°C. In favourable weather conditions, the lure (250 ml 50% ethanol denatured with 1% toluene) has to be replaced every 2-3 days. When catches reach 20 beetles per trap per day, the risk of attack of some importance is indicated.
For control of X. dispar in an endangered orchard or vineyard, eight traps per hectare need to be placed. Such a control system will reduce the beetle population and the damage considerably.
The red wing trap attracts a variety of other insect species (especially Diptera), but only a few honey bees and known natural enemies of insect pests.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
The economic damage caused by X. dispar is not easy to estimate. The beetle preferentially attacks stressed trees. Such trees might often have a chance of recovery without beetle attack.
In several countries of Europe and North America, X. dispar is sporadically a serious pest of fruit trees such as apple, apricot, peach, nectarine, pear, cherry and plum, and of hazel (Mathers, 1940; Linsley and MacLeod, 1942; Vasseur and Schvester, 1948; Schvester, 1954; Balachowsky, 1963; Postner, 1974; Viggiani, 1979; Mani and Schwaller, 1983; Hesjedal and Edland, 1988; Schick and Thines, 1988; Juillard-Condat and Perrau, 1989; Mani et al., 1990, 1992; Natali et al., 1994; Schröder, 1996; Lagowska and Winiarska, 1997; Saruhan and Tuncer, 2001). Less often, damage occurs in vineyards (Ioakimov, 1925; Russ, 1966; Mani et al., 1990, 1992). In the north-western states of America and western Canada, X. dispar is an important pest in chestnut (Castanea spp.) orchards (Bhagwandin, 1993; Kühnholz et al., 2003).
In most cases, only single trees or groups of trees are attacked and destroyed, but sometimes whole new plantings of young trees are severely damaged. This happens mostly in the second year after planting, to young plants in poor condition (Mani and Schwaller, 1983; Mani et al., 1992; Morone and Scortichini, 1998). In such cases, important economic losses can occur.
In European forests, losses due to X. dispar are sometimes important. Severe attack has been observed in young plantations of maple and oaks (Postner, 1974), of chestnut (Schvester, 1954; Bud, 1972), Chinese chestnut (Tsankov and Ganchev, 1988) and in some stands of birch, poplar and alder (Balachowsky, 1963). In Austria, sometimes massive attacks up to 4 m high have been observed both on fungus-infected and healthy trees of sycamore maple, ash, oak and cherry (Perny, 1998).