Tomicus Piniperda Research Articles

Effects of pruning young Scots pines on host vigour and susceptibility to Leptographium wingfieldii and Ophiostoma minus, two blue‐stain fungi associated with Tomicus piniperda

AbstractIn a field experiment in central Sweden, the vigour of 25‐yr‐old Scots pines was manipulated by pruning, prior to inoculation with Leptographium wingfieldii and Ophiostoma minus, two blue‐stain fungi associated with Tomicus piniperda. Our main purpose was to correlate fungus invasion and host defence reactions with host vigour. Both fungi invaded the inner bark and the sapwood at the points of inoculation. L. wingfieldii caused larger lesions in the bark, but O. minus tended to grow faster in the sapwood. The flow of primary resin was related to tree vigour, whereas carbohydrates present in needles and stem phloem were not. Lesion formation and the content or composition of resin acids in lesions did not differ between fungi or pruning treatments.

A statistical method for evaluating the abundance and colonization density of the pine beetle (Tomicus piniperda L.) on trap trees in Poland

The paper presents a statistical method for evaluating the abundance and colonization density of the pine beetle on trap trees. There was found a distinct linear correlation between the number of pine beetle galleries on 10% of the trap length from a butt and the number of galleries and colonization density over the whole trap.

Induced and spontaneous attacks by pine shoot beetles on young Scots pine trees: tree mortality and beetle performance

AbstractOvipositional attacks by the pine shoot beetles, Tomicus piniperda (L.) und T. minor (Hart.) (Col., Scolytidae) were induced on 72 young Scots pine trees (Pinus sylvestris L.) by baiting the trees with split pine bolts. Despite high attack densities of T. piniperda and reduced tree vigour due to repeated shoot‐feeding prior to attack, only eight trees died as a result of the induced attack. In the next year, spontaneous beetle attacks resulting in hundreds of dead trees occurred along a new stand edge. Ca 80 % of 106 dead trees grew within 2 m of the new stand edge. Twentyfive of the dead trees were felled together with adjacent living counterparts of the same size, and carefully inspected for beetle attack. All felled trees had been heavily attacked by T. piniperda. T. minor occurred in low numbers on some of the baited as well as spontaneously attacked trees. Killed trees of both categories were significantly more attacked by T. piniperda. Among baited trees, crown length, diameter and radial growth were larger for surviving trees than for killed ones. This was not the case for the pairs of spontaneously attacked trees. In both batches of trees, the critical attack density was ca 300 egg galleries per m2 on the lower stem. The high attack density required to overcome the resistance of the trees resulted in short galleries and a brood production below unity in all but three trees. Thus, both Tomicus‐species are dependent on dead or dying host material for their reproduction, and outbreaks on living trees cannot become selfperpetuating, not even in severely weakened stands.ZusammenfassungInduzierter und spontaner Befall junger Kiefernbäume durch den Großen und Kleinen Waldgärtner: Baumsterblichkeit und KäferentwicklungBei 72 jungen Pinus sylvestris aus 3 Bestandsreihen wurden Eiablage‐Angriffe von Tomicus piniperda und T. minor durch Anlockung mit frischem Kiefern‐Schnittholz induziert. Trotz hoher Angriffsdichte von T. piniperda und verminderter Baumvitalität durch Triebfraß der Käfer, starben von den manipulierten Bäumen nur 8 Stück durch die Käferangriffe ab. Im folgenden Jahr traten spontane Käferangriffe in durch Fällungen freigestellten Kiefern in der Nähe des Versuchsortes auf, die zum Teil zum Tod der Bäume führten. Von den abgestorbenen Bäumen wurden 25 Stück zusammen mit gleich vielen und gleich konstitutionierten, noch lebenden Bäumen gefällt und auf Käferangriffe hin beobachtet. Alle gefällten Bäume zeigten starke T. piniperda‐Angriffe. T. minor trat nur in geringer Anzahl sowohl an einigen manipulierten als auch an spontan befallenen Bäumen auf. Getötete Bäume beider Kategorien wurden von T. piniperda signifikant stärker angegriffen. Unter den manipulierten Bäumen waren Kronenlänge, Stammdurchmesser und Dickenwachstum bei den überlebenden Bäumen größer als bei den getöteten. Dies galt nicht für die spontan befallenen Bäume. In beiden Serien von Bäumen betrug die kritische Befallsdichte ca. 300 Muttergänge pro m2 am unteren Stamm. Die hohe Befallsdichte zur Überwindung der Resistenz der Bäume drückte sich in verkürzten Muttergängen der Käfer und einer Verringerung ihrer Brutgröße (mit Ausnahme von 3 Bäumen) aus. Somit sind beide Tomicus‐Arten von totem oder absterbendem Wirtsmaterial für ihre Reproduktion abhängig. Sie können an lebenden Bäumen nicht zur Massenvermehrung gelangen, selbst nicht in geschwächten Beständen.

Attacks of bark‐ and wood‐boring coleoptera on snow‐broken conifers over a two‐year period

The attacks of bark‐ and wood‐boring Coleoptera on broken conifer stems after severe snow‐breakage in early 1988 were studied in autumn 1988 and 1989. The study included twelve stands in the county of Värmland in central Sweden differing in age and edaphic conditions. The tops on the ground as well as the remaining rooted stem stumps of 94 Picea abies and 61 Pinus sylvestris were inspected. The presence of living branches on the stumps strongly influenced the incidence of insect attack. All stumps without branches were attacked during the two‐year period, whereas only a few spruce stumps with more than ten branches and no pine stumps with more than five branches were attacked. On spruce stumps, the most frequently encountered Coleoptera were all scolytids, i.e. the species Pityogenes chalcographus, Hylurgops palliatus, and the genera Polygraphus, Dryocoetes, and Trypodendron. On pine stumps, Tomicus piniperda was the most common species. Most of the spruce tops and virtually all pine tops were attacked during the two‐year period, and most of these attacks occurred during the first summer. P. chalcographus, Dryocoetes, and weevils of the genus Pissodes were the most frequent Coleoptera on spruce tops. On pine tops, the dominant insects belonged to the genera Pissodes and Pityogenes.

Attraction of bark beetles,Tomicus piniperda,Hylurgops palliatus, andTrypodendron domesticum and other insects to short-chain alcohols and monoterpenes

Several Scandinavian forest insects,Hylurgops palliatus, Tomicus piniperda, andTrypodendron domesticum (Coleoptera: Scolytidae),Rhizophagus ferrugineus (Coleoptera: Rhizophagidae) andPollenia spp. (Diptera: Calliphoridae) were attracted to window traps baited with ethanol and placed on Scots pine trees (Pinus sylvestris) in May-June, 1986. Release of ethanol at increasing relative rates of 0, 0.01, 0.1 and 1.0 (800 mg/day) from the window traps on trees in 1987 causedH. palliatus, T. domesticum, andR. ferrugineus to be increasingly attracted, whileT. piniperda was equally attracted at both 0.1 and 1.0 rates. The attraction ofT. piniperda to ethanol was weak compared to attraction to a monoterpene mix, (±)-α-pinene, (+)-3-carene, terpinolene. The terpene mix plus ethanol was significantly more attractive toH. palliatus than ethanol alone, but terpenes significantly reduced the attraction ofT. domesticum to ethanol. Baiting of pipe traps with a series of short-chain alcohols (methanol to hexanol) each alone showed that ethanol was greatly preferred byH. palliatus, T. domesticum, andR. ferrugineus over alcohols of one more or one less carbon, while longer-chain alcohols were not attractive. However,Glischrochilus hortensis (Col.: Nitidulidae) was attracted only to propanol. A series of 10-fold increasing release rates of ethanol (0.0001-1.0, where 1.0=800 mg/day) with either a "low" or "high" release of the terpene mix had various effects on the sexes during their attraction to pipe traps and subsequent entering of holes. Release of (-)-verbenone at 0.25 mg/day had no significant effect onH. palliatus orR. ferrugineus attraction to ethanol, but the response ofT. domesticum to ethanol was reduced. Several theories on olfactory mechanisms of host selection byT. piniperda are integrated and placed in ecological perspective.

Bark beetle attack on host logs reduced by spraying with repellents

AbstractColonization densities of the pine shoot beetle, Tomicus piniperda, and the ash bark beetle, Leperisinus varius, respectively, on bolts cut from Scots pine (Pinus sylvestris), and ash (Fraxinus excelsior) were significantly reduced after spraying the bolts with emulsion of synthetic verbenone or a plant oil containing predominately ipsdienone. In both bark beetle species, host odours play an important role in triggering aggregation behaviour while pheromones are of minor importance, if at all. In contrast, Ips spp. primarily aggregate in response to aggregation pheromones and spraying with verbenone or the plant oil, respectively, affected colonization of pine trap trees by Ips sexdentatus less strongly. While the plant oil had no effect, verbenone reduced the colonization to some extent.ZusammenfassungUntersuchungen zum Einsatz von Ablenkstoffen im Polterschutz gegen BorkenkäferDurch Zusatz eines Emulgators konnten hydrophobe Borkenkäfer‐Ablenkstoffe mit Wasser versetzt und analog Insektizidbrühen auf Holzpolter gespritzt werden. Als Ablenkstoffe kamen das synthetische Terpenketon Verbenon zur Verwendung sowie ein Pflanzenöl, das große Mengen des Terpenketons Ipsdienon enthielt. Die Behandlung von Kleinpoltern aus Kiefer (Pinus sylvestris) bzw. Esche (Fraxinus excelsior) reduzierte den Befall durch den Waldgärtner (Tomicus piniperda) bzw. den Eschenbastkäfer (Leperisinus varius) signifikant, während unbehandelte Vergleichspolter starken Käferbefall aufwiesen. Beide Borkenkäferarten sind Frühschwärmer, und die Aggregation wird im wesentlichen durch Wirtsduftstoffe ausgelöst; käfereigene Aggregationspheromone spielen keine bzw. nur eine untergeordnete Rolle. Im Gegensatz dazu schwärmt der Große Kiefernborkenkäfer (Ips sexdentatus) erst bei länger anhaltenden hohen Lufttemperaturen, und die Käfer lösen die Aggregation durch Pheromone aus. Bei I. sexdentatus ergab die Behandlung von Fangbäumen mit den Ablenkstoff‐Emulsionen weniger klare Befunde als bei T. piniperda oder L. varius. Während das Pflanzenöl offenbar überhaupt keinen Einfluß auf den Befall der Fangbäume hatte, verringerte das Verbenon den I. sexdentatus‐Befall geringfügig. Auch die punktförmige Applikation eines Ablenkstoffes in Polyethylenbeuteln hatte keinen Einfluß auf die Besiedlung von Lärchen‐Fangbäumen (Lanx decidua) durch den Lärchenborkenkafer (I. cembrae).

Height growth recovery and crown development in top‐damaged Pinus sylvestris trees

Leader shoot damage was imposed on young Scots pines (3 m high) in four ways: by caging the uppermost whorl including the leader shoot with 10 pine shoot beetles; by caging the two uppermost whorls with 20 beetles; by topping the tree below the 1984 whorl; by topping the trees as above and removing all current shoots in whorl 1983. Six years later, top‐damaged trees were still significantly shorter than undamaged controls, although the annual height growth rate had recovered to the pre‐damage level within 3 years. Recovery occurred in two ways: lateral branches from the nearest intact whorl took dominance over the damaged leader or secondary branches developed from interfascicular buds on the damaged leader shoot. Approximately one and two years of height growth were lost in the former and latter case, respectively. Only 5 of the 34 top‐damaged trees escaped technical defects (crooks and/or vertical branches). Stem diameter and crown development were slightly affected.

Leptographium and Graphium species associated with pineinfesting bark beetles in England

Isolations for blue-stain fungi were made from Hylastes ater, H. opacus, Hylurgops palliatus and Tomicus piniperda trapped in Pinus sylvestris billets. Five Leptographium spp. including one of unknown identity and two apparently undescribed Graphium spp. were isolated. One of the Leptographium spp. identified as L. truncatum is thought to be synonymous with L. lundbergii. This is the first record of Leptographium procerum, L. serpens and L. wingfieldii from the United Kingdom. Leptographium lundbergii has previously been found in the country.

Simulation of the mate-finding behaviour of pine shoot beetles, Tomicus piniperda

An algorithm for animal searching behaviour was constructed that allows independent variation at random of movement parameters such as speed, duration, step size, and maximum right or left turn angle. The area, radius of the object searched for, and number of objects and searchers can also be varied. A capture algorithm is presented that can determine whether a searching animal intercepts a circle (object) irrespective of the step size. These two algorithms were incorporated into a computer simulation model of mate finding for walking male bark beetles, Tomicus piniperda, in search of females that remained stationary when boring into the bark of Scots pine, Pinus sylvestris. The model showed that, for realistically chosen parameters, males were able to find ‘females’ at apparently natural rates without the need to enlarge the radius of the ‘female’ beyond the size of an actual female. This indicates that there may be little, if any, advantage in the evolution of a long-range pheromone, for which no chemical and behavioural evidence has yet been found.

Application of deltamethrin for spraying or dipping to protect Scots pine seedlings against Hylobius abietis L and logs against Tomicus piniperda L

Summary — The authors compared the efficiency of protecting Scots pine trees against Hylobius abietis L, the large pine weevil, using deltamethrin (Decis 2.5 EC) by dipping seedlings before planting and by spraying after planting. Assessment of damage caused by the beetles and the rate of degradation of the insecticide on the plants proved that dipped seedlings were less frequently damaged and were protected by 10 times the quantity of active insecticide ingredient than sprayed plants. Experiments were also carried out to analyse the application of deltamethrin in the protection of wood before bark stripping against Tomicus piniperda L, the pine-shoot beetle. Treatments were carried out after the last frosts in the early spring and during the first days of swarming. Analysis of infested wood and the degradation of the deltamethrin in the bark showed a high degree of insecticide persistence and thus the possibility of efficient protective treatment 2-3 wk before the swarming period.

The Pine Shoot Beetle Tomicus piniperda as a Vector of Blue Stain Fungi to Windblown Pine

The Pine Shoot Beetle <i>Tomicus piniperda</i> as a Vector of Blue Stain Fungi to Windblown Pine

Breeding efficiency in Tomicus piniperda and shoot damage after late autumn thinning of young Pinus sylvestris stands

The breeding of the pine shoot beetle (Tomicus piniperda) after thinning of young Scots pine stands in late autumn, and subsequent shoot damage, were studied in southern, central and northern Finland during three successive years (1977–79). No distinct increase in the attack density or beetle population was observed on the felled trees during the study period. Shoot damage on the standing trees remained low, and was not considered to have any marked negative effect on tree growth or further development of the pine stand. No noticeable difference was found between the different parts of the country. The economic importance of beetle damage resulting from late autumn thinnings was estimated to be low.

Monoterpene composition of the preformed and induced resins of Scots pine, and their effect on bark beetles and associated fungi

AbstractInoculations of fungi or introductions of insects were performed on Scots pines. The monoterpene composition of the induced resin differed from that of preformed resin, but did not depend on the nature of the aggression on a same tree. There were variations in the composition of induced resin according to tree. Mycelial growth was strongly limited, more by the increase in resin quantity and total monoterpene quantity than by the qualitative changes of the monoterpene composition. Monoterpenes appeared very toxic for Tomicus piniperda, but not for Ips sexdentatus.

Colonization pattern in the pine shoot beetle, Tomicus piniperda: Effects of host declination, structure and presence of conspecifics

AbstractA survey of 100 Scots pine trees (Pinus sylvestris) showed that those windthrown with a declination &gt; 50° from vertical were preferentially colonized by the larger pine shoot beetle, Tomicus piniperda (L.) (Coleoptera: Scolytidae). A factorial experiment was done with logs of 0°, 45° and 90° declination, and different diameters and spacing to test hypotheses, involving olfactory, visual and tactile mechanisms. In the experiment, the attack rates depended strongly on log diameter with a preference being shown for larger diameter logs having a rough bark structure. In contrast to the field survey, experimental declination did not increase attack densities. The spacing between neighbouring attack sites in the bark was regular rather than random, which could be due both to spacing between conspecifics and regularities in bark structure. The contrary data from survey and experiment is explained by release of odours from wind damaged trees, and host odour and bark roughness stimuli are suggested to operate in different steps in the behavioural sequence of host location and colonization.RésuméConditions de la colonisation des pins par Tomicus piniperda: effets de l'inclinaison, de la structure de l'hôte et de la présence de congénèresL'observation de 100 individus de Pinus sylvestris a montré que les arbres inclinés de plus de 50° par le vent sont colonisés de préférence par T. piniperda L., Scolytidae. Des expériences avec des branches de différents diamètres, plus ou moins espacées et inclinées de 0°, 45° et 90°, ont permis d'examiner les influences de l'olfaction, de la vision et du tact. Les attaques ont montré une préférence marquée pour les diamètres les plus grands et pour la structure la plus rugueuse. Contrairement aux observations dans la nature, l'inclinaison n'a pas augmenté les attaques.L'analyse sur l'écorce de la distance entre les points d'attaque montre une tendance à une distribution régulière plutôt qu'au hasard, tenant compte de la régularité structurale de l'écorce.Les résultats contradictoires entre les expériences et les observations peuvent s'expliquer par l'abondante émission d'odeurs par les arbres endommagés par le vent, paramètre non contrôlé dans les observations. Les stimuli dus à la rugosité et à l'odeur de l'arbre devraient opérer à différentes étapes de la découverte et de la colonisation de l'hôte.

Duct resin flow in Scots pine in relation to the attack of the bark beetle Tomicus piniperda (L.) (Col., Scolytidae)

AbstractThe spring onset of the duct resin flow in Scots pine, Pinus sylvestris L., was studied in relation to the start of the flight period of the pine shoot beetle, Tomicus piniperda (L.), during four years. Plastic tubes fitted into holes cut into the cambium of the trees were used to measure the resin flow. In one experiment the resin flow in low and high vigor trees was measured and related to the outcome of induced T. piniperda attacks.In all four years the duct resin flow had started in most of the experimental trees by the onset of the flight period of T. piniperda. There was large variation in the amount of resin exuded from different places on the same tree. Despite this variation it was possible to rank the trees with regard to the mean amount of exuded resin. The ranking thus obtained was consistent for two sets of measurements.The resin flow did not physically prevent beetles from establishing galleries in resistant trees. No “pitching out” of beetles was observed, and a relatively long time passed before the beetles started to leave the unsuccessful galleries. Induced attacks were successful only in two of fifteen low vigor trees. Although these two trees were characterized by a low resin flow some of the high vigor trees also exuded equally low amounts.ZusammenfassungHarzfluß der Kiefer in Beziehung zum Befall des großen Waldgärtners, Tomicus piniperda (L.) (Col., Scolytidae)Es wurde 4 Jahre lang der Beginn des Harzflusses im Frühjahr bei Pinus sylvestris in Beziehung zu Start und Flugzeit von T. piniperda untersucht. Zur Messung des Harzflusses wurden Plastikröhrchen in die Rinde der Bäume bis zum Kambium eingesetzt. In einem Experiment wurde der Harzfluß bei Bäumen unterschiedlicher Vitalität gemessen und zum Befallserfolg von T. piniperda in Beziehung gesetzt. In alien 4 Jahren hatte der Harzfluß bereits begonnen, als die Flugperiode des Borkenkäfers einsetzte. Die Harzmenge variierte an verschiedenen Stellen desselben Baumes erheblich. Trotzdem war es möglich, die Bäume nach der mittleren Menge ihrer Harzausscheidung zu ordnen. Die ermittelte Rangordnung war in zwei Meßserien die gleiche. Der Harzfluß hinderte die Käfer nicht daran, in widerstandsfähigen Bäumen Brutgänge anzulegen. Die Käfer wurden nicht durch den Harzfluß ausgetrieben oder getötet, und es dauerte relativ lange, ehe die Käfer die ungeeigneten Brutgänge verließen. Der Befall war nur in 2 von 15 Bäumen geringer Vitalität erfolgreich. Obwohl diese Bäume geringen Harzfluß aufwiesen, zeigten auch einige Bäume höherer Vitalität geringen Harzfluß.

Spatial distribution of crown damage and growth losses caused by recurrent attacks of pine shoot beetles in pine stands surrounding a pulp mill in southern Sweden

AbstractCrown damage and growth losses caused by the shoot‐feeding of Tomicus piniperda (L.) and T. minor (Hart.) (Col., Scolytidae) were studied in pine forests surrounding a timber yard established in 1977 at a pulp mill in southern Sweden. During 1978–1982, the level of beetle attack was monitored by counting beetle‐pruned shoots on sample plots along survey lines extending 1800 m away from the timber yard. In 1983, increment cores were taken from a total of 324 pine and 63 spruce trees growing on the same sample plots.The spatial distribution of fallen shoots indicated very high attack levels (occasionally exceeding 100 shoots per m2 on the ground) within 500 m, modest attacks up to 1000–1500 m and low attack levels at the end of survey lines. In general, the number of fallen shoots decreased after the first year, especially close to the timber yard, but a tendency towards increasing damage at further distances was observed.All age classes of pine stands within 500 m from the timber yard displayed reduced radial growth soon after 1977 as compared to pine stands beyond 1000 m. Using pre‐damage growth as a reference, the relative basal area during the period of damage (1978–1982) was reduced by nearly 50%, 30% and 20% within 200, from 200 to 500 and from 1000 to 1500 m from the timber yard, respectively, whereas the pines beyond that distance and all spruces displayed no change in relative basal area growth.Thus, the similarity in damage and growth patterns strongly indicates that the observed growth losses do emanate from beetle‐infested pulp wood at the timber yard.ZusammenfassungRäumliche Verteilung der von wiederholtem Waldgärtner‐Befall verursachten Kronenschäden und Zuwachsverluste in Kiefernbeständen in der Umgebung eines Holzlagerplatzes in SüdschwedenDie räumliche Verbreitung von Kronenschäden und Zuwachsverluste, die von dem wiederholten Triebfraß der Waldgärtner [Tomicus piniperda (L.) und Tomicus minor (Hart.), (Col., Scolytidae)] verursacht worden sind, wurden in Kiefernbeständen in der Umgebung einer Papierfabrik in Südschweden untersucht. Ein neuer Holzlagerplatz wurde im Jahre 1977 in Betrieb genommen. Die vom Waldgärtner befallenen und herabgefallenen Triebe wurden zwischen 1977 und 1982 auf Probeflächen entlang 1800 m langen Taxierungslinien gezählt. Im Jahre 1983 wurden auf den Probeflächen Zuwachsraten von 324 Kiefern und 63 Fichten mit dem Zuwachsbohrer entnommen.In einer Entfernung von 500 m vom Holzlagerplatz deutete die räumliche Verteilung von herabgefallenen Trieben sehr starken Waldgärtner‐Befall an (in einigen Fällen mehr als 100 Triebe pro m2 auf dem Boden). Der Bereich zwischen 1000 und 1500 m Entfernung zeigte mittleren Befall und in größerer Entfernung waren die Schäden gering. Im allgemeinen sank die Anzahl der Triebabbrüche nach dem ersten Jahr des Befalls, besonders in der Nähe des Holzlagerplatzes. Bei größerer Distanz zeigten die Schäden aber eine zunehmende Tendenz.Alle Altersstufen der Kiefernbestände innerhalb von 500 m vom Holzlagerplatz entfernt zeigten im Vergleich mit Beständen in mehr als 1000 m Entfernung schon kurz nach dem Beginn der Lagerung einen reduzierten Zuwachs. Im Vergleich mit dem Zuwachs vor dem Befall war der relative Grundflächenzuwachs der Befallsperiode (1978–1982) mit 50% innerhalb von 200 m, 30% zwischen 200 und 500 m und 20% zwischen 1000 und 1500 m Abstand vom Lagerplatz reduziert. Kiefernbestände in noch größerem Abstand erlitten keine Reduzierung des Grundflächenzuwachses. Fichtenbestände zeigten keine Zuwachsverluste, unabhängig von der Entfernung zum Holzlagerplatz.Die Verteilung der Triebschäden und der Zuwachsverluste folgten dem gleichen Muster. Demnach waren die Zuwachsverluste mit großer Wahrscheinlichkeit von Waldgärtnern verursacht und die Schäden durch Käfer aus befallenem Kiefernholz des Holzlagerplatzes hervorgerufen.

Plant constituents as signals for aggregation and attack of pest insects

Abstract

Cinétique de croissance des champignons associés à lps sexdentatus Boern et Tomicus piniperda L (Coleoptera : Scolytidae) et des réactions de défense des pins sylvestres (Pinus sylvestris L) inoculés

Summary — Kinetics of growth of fungi associated with lps sexdentatus and Tomicus piniperda (Coleoptera: Scolytidae) and of the defence reaction of the inoculated scots pines. At 3 different seasons in the year, 5 species of fungi associated with I sexdentatus and T piniperda were inoculated into scots pine trees. Logs were also inoculated once during the year in the lab. The reactions were estimated by their length and by the quantity of resin (both total and concentration). The percentage of sieve cells filled with resin was appreciated by histological sections made in each reaction, at 10 and 30 mm from the point of inoculation and in the middle between this point and the end of the reaction. The kinetics of growth of the fungi and of the defence reactions (length, resin, histology) were followed for 60 days. The temperature and defence reactions were not sufficient to explain the differences in the kinetics of growth between fungi and between seasons (figs 1 and 7). Factors related to intrinsic characteristics of the fungi and to physiological state of the tree may play a role. The possible role of each fungus is discussed according to the induction of the reaction and to tree death when attacked by bark beetle populations. The wound periderm does not seem to be directly responsible for stopping the fungal growth. In return, the considerable slowing down of this growth, followed by a slowing down of the development of the reaction length (fig 3) may give sufficient time for the wound periderm to be built, to insulate the wounded tissues completely and to contain the aggressors. The parallel between the kinetics of growth of the fungi and the kinetics of resin accumulation suggests that the quantity of resin would depend upon the quantity of elicitor produced during the fungal growth. The reaction length in the phloem would depend on the diffusion ability of the elicitor. The end of the resin accumulation at a given place would not depend upon tissue saturation, but rather on the end of the elicitation at this place (compare figs 3, 5 and table III). After the end of the reaction growth, an homogenization process of the resin distribution may take place inside the reaction, by a diffusion of the resin from the highly concentrated zones to the less concentrated zones and, in some cases, by a continuation of the resin synthesis. A definition of 3 parameters representative for the defence reaction is proposed: speed, intensity, efficiency.

A model for the timing of swarming of Tomicus piniperda (Coleoptera: Scolytidae)

Tomicus piniperda is the first bark beetle to swarm in the spring in Fennoscandia. The intensity of swarming is directly related to air temperature above a certain threshold and reaches 100% asymptotically. While temperature sums above the threshold accumulate, swarming rate slows down. A non‐linear model was built on these considerations. The model was calibrated to window trap material from northern Finland, and it was validated against published material mainly from Norway. The threshold temperatures in these materials were 10.8°C and 11.6°C, respectively. The predictions of the model were satisfactory, and the model will be tried as a part of an entire population dynamics model. The possibilities to predict not only timing, but also the frequency of attack are discussed.

Host tree unsuitability recognized by pine shoot beetles in flight

In spring, the landing rate of flying European pine shoot beetles,Tomicus piniperda L., on injured Scots pine diminishes as colonization continues. This is due to olfactory cues that indicate progressive host degradation. Verbenone was shown to play a role in the beetle's recognition of this unsuitability of a formerly suitable host, since the compound was increasingly released from colonized tree sections as they aged, but not from uninfested sections. Also, the release of verbenone at natural rates in the forest inhibited the attraction of beetles to host monoterpenes.