One or more of the features that are needed to show you the maps functionality are not available in the web browser that you are using.
Please consider upgrading your browser to the latest version or installing a new browser.
More information about modern web browsers can be found at http://browsehappy.com/
As both T. piniperda and T. minor are dependent on a continuous supply of suitable host material for their survival, silvicultural and logging practices may greatly affect the population density of these beetles both locally and regionally. The concept of forest hygiene, i.e. keeping the amounts of brood material available for bark beetles during their flight period as low as possible, has long been a key strategy in forest protection (Escherich, 1923; Speight and Wainhouse, 1989; Dajoz, 2000). This means that silvicultural operations should be carried out with a minimum of suitable host material left in the forests, that snow-breaks and wind-falls should be cleared up before beetle attack or at least before beetle emergence, and that the timber should be removed from the woods in due time. All this is easier said than done, and when beetle outbreaks occur, trap trees are the common method used to reduce the populations (e.g. Escherich, 1923; Hanson 1937, 1940).
A major change took place in forestry operations after World War II when the timber, which had until then mainly been debarked in the forests prior to transportation (often by floating), was instead stored unbarked along road sides until it was taken to the industry by trucks. In contrast to earlier practice, forest operations were also conducted all-year-round. This created a entirely new situation with huge amounts of unbarked timber stored in the forests during beetle flight, especially in Fennoscandia, where annual cuttings were large and roads often unaccessible during the thawing period in spring. Little has been written about this phenomenon, leading to constantly elevated bark beetle populations (Eidmann, 1985, 1992; Jääskelä et al., 1997; Day and Leather, 1997).
In Sweden, the huge storm-felling in 1969 when 20 million m³ blew down, resulted in bark beetle outbreaks of unprecedented magnitude (Nilsson, 1976) and a similar situation developed in Finland a few years later (Annila and Petäistö, 1978). These events eventually led to changes in the forestry legislation when forest protection became regulated by law (Eidmann 1985, 1992; Jääskelä et al., 1997). In principle, unbarked timber must not be stored during the flight and emergence of pine and spruce bark beetles, unless certain precautions are taken. In Sweden, up to 5 m³ of storm-felled trees per hectare can and should, according to the current debate about dead wood and biodiversity (Ehnström et al., 1995), be left without countermeasures being taken. Similar legislation exists in other European countries.
Thus, the main option to avoid bark beetle damage was, and still is, rapid transportation (i.e. before beetle flight in spring) of saw logs and pulpwood from the forest to the industry, where it is barked or submerged in water immediately, until processed. In Sweden, where timber storage and fallen Tomicus-attacked shoots were monitored nation-wide through the 1970s and 1980s, a substantial reduction in Tomicus populations was recorded with decreasing timber storage figures. Growth losses nowadays mainly occur around saw and paper mills with constant timber storage (e.g. Långström and Hellqvist, 1990; and many unpublished reports) for at least a decade.
If timely transportation is not feasible, the timber can be protected in different ways. The earlier barking at the felling site is now abandoned as being too expensive. Instead, the timber can be protected by spraying with insecticides, but this has to take place before beetle flight. In the 1980s, synthetic pyrethroids such as permethrin became the main option (Srot, 1968; Doom and Luitjes, 1970; Novak, 1972; Dowding, 1974; Dominik and Kinelski, 1979; Szmidt, 1983; Glowacha and Wajland, 1992). Due to increased environmental concerns, the use of insecticides for timber protection has decreased greatly, at least in Fennoscandia. Also, spraying against the early flying Tomicus species may be tricky under northern conditions, as snow may sometimes still cover part of the timber resulting in poor spray coverage.
Other ways of protecting log piles against bark beetles have been explored. Covering pulpwood stacks with plastic or other coatings has produced variable, but sometimes satisfactory, results, i.e. comparable to insecticide use, in Sweden and Finland (Dehlen and Nilsson, 1976; Heikkilä, 1978; Jääskelä et al., 1997). Partial debarking or removal of the upper layers in the pines also reduced beetle production substantially (Dehlen et al., 1982; Jääskelä et al., 1997) as did sprinkling with water (Regnander, 1976). A more modern approach is based on deterring the beetles from attacking by spraying log piles with verbenone or other substances with deterrent properties (Schlyter et al., 1988; Baader and Vité, 1990; Kohnle et al., 1992; McCullough et al., 1998). Non-host volatiles also show some promise for timber control (McCullough et al., 1998; Zhang, 2001) but none of these techniques has yet attained any wide use in practical forestry.
Baited traps containing host odours, especially alpha-pinene, attract large numbers of pine shoot beetles, and these are excellent for monitoring purposes but give little hope for beetle control. The recent detection of trans-verbenol, which may act as an aggregation pheromone in T. piniperda (Poland et al., 2003), may provide an even better monitoring tool but hardly a control option.
Another important approach to maintaining low beetle populations is related to the timing of silvicultural operations such as cleaning (i.e. precommercial thinning) and thinning of pine stands (Bykov, 1987). In general, late summer operations are preferred as the waste wood is neither attacked in the year of cutting (beetle flight terminated), nor in the following spring (waste wood unsuitable). In Fennoscandia, June to September are considered to be 'Tomicus-safe' months (Långström, 1979; Annila and Heikkilä, 1991), whereas Postner (1974) recommends August for central Europe. Cleanings should preferentially be made before DBH (diameter at 1.3 m stem height) exceeds 3 cm, i.e. before thick bark starts to form on the lower stem and the trees become suitable for T. piniperda (Butovitsch, 1954; Långström, 1979).
Some attempts at biological control of T. piniperda have been made using the entomopathogenic fungus Beauveria bassiana with variable results (Nuorteva and Salonen, 1968; Bychawska and Swiezynska, 1979). Lutyk and Swiezynska (1984) obtained satisfactory results when logs were covered with plastic after spraying with B. bassiana. The introduction of the clerid beetle T. formicarius to North America has been seriously considered (Haack and Poland, 2001) but this approach may now be redundant as the native and closely related clerid T. dubius seems to have adapted to the new prey (Kennedy and McCullough, 2002).
The economic impact caused by the pine shoot beetles is threefold: firstly, growth losses may be caused by extensive shoot-feeding in the pine crowns; secondly, stem attacks cause tree mortality; and thirdly, deterioration of timber quality may occur due to beetle-vectored blue-staining of saw logs and pulpwood.
In T. piniperda, the third type of damage is the least problem, mainly because the forest industry has developed routines to avoid timber damage by timber insects including pine shoot beetles. Compared to T. minor, the blue-staining caused by T. piniperda occurs less frequently in timber and is often more superficial, but it still poses a major problem, as indicated by a series of Finnish studies, because T. piniperda is so common (Löyttyniemi and Uusvaara, 1977; Uusvaara and Löyttyniemi, 1978). Recently, sap staining of Korean pine logs due to T. piniperda attack was reported as a timber storage problem in Korea (Kim et al., 2002). No estimates of the economic losses due to blue-staining caused by T. piniperda are available, but the presence of any blue-staining in conifer saw logs reduces the value to a fraction (ca 20%) of the price of prime timber on the timber market, hence, saw mills have developed timber handling practices that minimise insect damage. Although some blue-staining is acceptable in pulpwood, there is a cost connected to the processing of blue-stained timber, as more chemicals are needed for bleaching (Löyttyniemi et al., 1978).
In contrast to the spruce bark beetle (Ips typographus) and a few other aggressive bark beetles, T. piniperda cannot overwhelm and kill healthy pine trees, probably because it lacks aggregation pheromones. Thus, tree mortality due to pine shoot beetle attacks occurs only when trees are weakened by some other cause such as defoliation, fire damage, drought stress, flooding, etc. There are several European examples of defoliator outbreaks rendering pine trees susceptible to pine shoot beetle attacks (Saalas, 1929; Butovitsch, 1946; Lekander, 1953; Crooke, 1959; Habermann and Geibler, 2001; Långström et al., 2001; Cedervind et al., 2003), but tree mortality varies from a few to more than 50% of trees. In the worst case, 2 years of severe to total defoliation led to ca 50% pine mortality over a 5-year period, half of which was attributed to T. piniperda, whereas stands sprayed with Dimilin suffered 1 year of defoliation, no mortality and modest growth losses (Långström et al., 2001). In another case, beetles caused substantial tree mortality after 1 year of defoliation (Crooke, 1959), whereas normally such defoliation would result in only a few and mainly suppressed trees dying from subsequent beetle attack (Lekander, 1953; Cedervind et al., 2003). Each defoliation case is unique and difficult to generalise; however, in most cases studied, trees with less than 10% of the normal foliage left are in great danger of fatal beetle attacks, whereas trees with more than 30% foliage are safer.
Pine trees may also become susceptible to Tomicus attack by fungal diseases. There is one report from Denmark (Jörgensen and Bejer-Petersen, 1951) and from Poland (Sierpinski, 1969), and several from Russia (Bogdanova, 1988, 1998; Kolomiets and Bodganova, 1992) showing that the root rot fungus (Heterobasidion annosum) may predispose pine trees to fatal attacks by T. piniperda. Similarly, pine shoot beetle attacks have followed outbreaks of the fungal shoot disease (Gremmeniella abietina) in Fennoscandian pine forests (Kaitera and Jalkanen, 1994; Cedervind, 2003). Industrial pollution may also render pine trees susceptible to beetle attacks (Sierpinski, 1971; Krol, 1980; Duda, 1981; Oppermann, 1985; Heliövaara and Väisänen, 1991; Kolomiets and Bogdanova, 1998). Forest fires, which are an integral part of the boreal pine ecosystem, have often been found to render trees susceptible to pine shoot beetle attacks in both northern (Galaseva, 1976; Agafonov and Kuklin, 1979; Bogdanova, 1986; Ehnström et al., 1995; Luterek, 1996; Långström et al., 1999) and southern (Markalas, 1997; Fernandez and Costas, 1999) parts of the pest's distribution range.
Only in the Mediterranean region, does significant tree mortality occur on seemingly healthy or only slightly weakened trees of different pine species due to stem attacks by T. piniperda and/or T. destruens (Triggiani, 1983; Ben Jamaa et al., 2000). Drought stress probably caused a major outbreak of T. piniperda and other bark beetles in central France in the 1980s (Sauvard et al., 1988). Only at exceptional attack densities can beetles kill seemingly healthy pines in Scandinavia (Långström and Hellqvist, 1993).
The situation in China differs drastically from that in Europe, in that large-scale tree mortality attributed to T. piniperda has occurred in plantations of Yunnan pine (Pinus yunnanensis) during the past decade (Ye, 1991; Lieutier et al., 2003). Although these trees may suffer some drought stress from time to time, another more important explanation for these outbreaks is that intensive shoot damage may render the trees susceptible to further stem attacks, leading to a vicious self-perpetuating cycle (Lieutier et al., 2003). There are also signs of beetle aggregation during shoot feeding to certain tree individuals (Ye and Lieutier, 1997). There is now some evidence that this beetle, hitherto referred to as T. piniperda, may in fact be another Tomicus species (Lieutier et al., 2003).
In Europe, the growth losses following shoot feeding by pine shoot beetles constitute the main problem, and most of that is due to T. piniperda (Escherich, 1923; Hanson, 1937; Speight and Wainhouse, 1989). These growth losses have mainly been studied in Sweden (Mattson-Mårn, 1921; Andersson, 1973; Nilsson, 1974, 1976; Långström and Hellqvist, 1990, 1991) and Poland (Michalski and Witkowski, 1960; Borkowski, 2001). All of these studies demonstrate a reduction in growth with increasing damage levels, but growth reduction is easier to quantify than levels of damage. Nilsson (1974) claimed that high growth losses occurred at an estimated damage level of 100-150 lost shoots per tree (calculated from felled trees at the end of the study period); however, experiments with caged beetles or artificial shoot pruning did not verify this damage/loss relationship (Ericsson et al., 1985; Långström et al., 1990), implying that the damage levels were underestimated by Nilsson (1974). Later, Långström and Hellqvist (1991) established that 3 years of timber storage resulted in ca 1000 lost shoots, corresponding to more than half of the total needle biomass and a 75% loss in volume growth during the 3-year period (and 65% in basal area growth response during 6 years) on nearby trees. Damage levels and growth losses declined quickly with increasing distance to the timber yard, but could still be traced at a distance of 500 m. Borkowski (2001) found a similar pattern, with radial increment reduced to ca 50% within 300 m from the saw mill, and the number of fallen shoots more than five-fold in that area compared to more distant areas. A similar case was reported from New York State, USA (Czokajlo et al., 1997).
During the large bark beetle outbreaks in Sweden following the huge wind-throw in autumn 1969, when ca 20 million m³ of pine and spruce blew down, Nilsson (1976) estimated that pine shoot beetles caused growth losses in Sweden of several million cubic metres per year in the early 1970s. These figures were based on nation-wide surveys of fallen shoots, which were converted to growth losses, but these losses were overestimated as they were based on his damage/loss ratios (Nilsson, 1974) discussed above.
The number of fallen shoots can be used to estimate the size of the local population of pine shoot beetles. It has been said that one shoot roughly corresponds to one beetle, at least under Swedish conditions. The fallen shoots are best counted in early spring and are often expressed per square metre of soil surface, and knowing the stem density, the attack level per tree can be derived. In well-managed Swedish pine forests with only occasional suppressed trees dying in the stands, the baseline level seems to be around 0.2 shoots per m² and year corresponding to ca 2000 beetles per hectare and a few beetles per tree, with a stem density ranging from ca 2000 in pole-sized stands to ca 500 in mature pine stands (Långström and Hellqvist, 1990; Ehnström et al., 1995). In a Polish study, the baseline figure was around 0.5 shoots/m² (Borkowski, 2001). In central France, the corresponding figure ranged from 0.2 to 0.4 shoots/m², but the presence of any kind of brood material was directly reflected in elevated numbers of shoots and beetles (Sauvard et al., 1987).
In early thinnings or precommercial cleanings, the stumps produced a few tens of beetles per stump increasing linearly with stump diameter (range 5-15 cm), while the corresponding cut stem produced up to 200 beetles (no T. minor, only T. piniperda) per tree (Långström, 1979). Maximum shoot numbers were ca 20 shoots/m² corresponding to population levels of ca 200,000 beetles per ha, and ca 200 lost shoots per tree. The expected volume growth loss after this 1-year attack should have been ca 10% during a 5-year period (cf. Elfving and Långström, 1984; Ericsson et al., 1985). In older thinning stands, the logs are removed and hence only the stumps and the slash are available for the beetles to breed in. Consequently, Doom and Luitjes (1971) found in The Netherlands that beetle levels were low in thinnings when the stems were removed, and that leaving the stems caused severe shoot damage, ca 20 foliage losses.
In clear cuts in Sweden, mature pine stumps produced, on average, ca 150 pine shoot beetles (T. piniperda only) per stump (Hellqvist, 1984). The logging waste, i.e. the cut tree tops, produced no beetles of T. piniperda (bark too thin), whereas a highly variable number of T. minor beetles could be produced in the tops. In one case, the number of egg galleries increased from zero to more than a thousand when the diameter (measured at the base of the cut top) increased from 5 to 15 cm, and ca 400,000 beetles were estimated to have emerged per hectare from 250 tops (Lekander, 1974).
Compared to these cases, storm-felled trees as well as snow-breaks may produce substantially more bark beetles, due to the fact that the whole tree may be colonized by pine shoot beetles when both T. piniperda and T. minor are present in the area. Such trees may produce tens of thousands of beetles (mainly T. minor) when they are fully colonized (Långström, 1984), but the occurrence of T. minor is highly variable and unpredictable, even in areas where it should be present (Annila and Petäistö, 1978; Führer and Kerck, 1978a, b; Långström, 1984). In cases of large storm fellings, many trees may escape beetle attack in the first year for two reasons. Firstly, there may not be enough beetles to colonize all the brood material that is suddenly available, and secondly, some of the trees may display residual resistance due to live root contacts fending off the attacking beetles (Annila and Petäistö, 1978; Führer and Kerck, 1978a; Långström, 1984; Saarenmaa, 1987). The abundance in brood material often leads to high brood production in the first year, and in the second year the remaining trees are heavily attacked, and brood production goes down due to intraspecific competition (Annila and Petäistö, 1978; Långström, 1984).
During the 1970s, the main concern regarding pine shoot beetles was related to the widespread storage of unbarked pulp wood in the forests during the swarming and emergence periods of the beetles, which supported high and stable population levels and subsequent common shoot-feeding damage in pine stands, at least in northern Europe (Nilsson, 1976; Speight and Wainhouse, 1989). The colonization of pulpwood stacks by pine shoot beetles (only T. piniperda as T. minor was seldom found below the top layer) varied with latitude, exposure (shading) and type of wood stored (i.e. the proportion of timber with rough bark). More beetles emerged from exposed stacks than from shaded ones in central Sweden (Långström et al., 1984), and in northern Fennoscandia few beetles emerged at all from the inner parts of the stacks (Juutinen, 1978; Saarenmaa, 1985). The mean beetle production per cubic metre of stored timber is therefore very difficult to estimate: Juutinen (1978) gives a figure of 4400 for the upper log layers, but Långström et al. (1984) considered 2000 as a more realistic mean value for this kind of breeding material. A truck load of pulpwood would then produce tens of thousands of beetles that fly to nearby pine stands for shoot feeding and subsequent growth losses. Recognition of this situation and knowing the huge amounts of timber cut annually, for example, in Finland and Sweden, has led to changes in the forest protection legislation in these and other countries, resulting in a drastic reduction in the storage of unbarked timber (see Control).
Poor forest protection practice with common timber storage along forest roads has not only caused shoot damage and growth losses, but has also maintained high beetle populations that can erupt when storm-fellings or snow-breaks suddenly make huge amounts of brood material available locally or on a regional scale, such as occurred in Sweden after the storm in November 1969 when 20 million m³ blew down and started the outbreak of T. piniperda and Ips typographus (Nilsson, 1976). Similar scenarios have occurred in many parts of Europe during the twentieth century (Escherich, 1923; Niemeyer and Thalenhorst, 1974; Luitjes, 1976, 1977; Annila and Petäistö, 1978; Führer and Kerck, 1978a, b; Bychawska, 1983; Winter and Evans, 1990). The economic consequences of these beetle outbreaks have seldom been established.