Susceptibility of Sitka spruce and grand fir trees to decay by Heterobasidion annosum

The susceptibility of Sitka spruce (Picea sitchensis) and grand fir (Abies grandis) to decay by Heterobasidion annosum was compared on a site with a previous history of serious disease. The incidence of decay 15–16 years after planting was 1.5% in grand fir, compared with 34.8% in Sitka spruce. These results are broadly similar to those reported from other trials. More information is required for older trees in Britain but the evidence so far available suggests that grand fir is more resistant to H. annosum than Sitka spruce. Planting grand fir on severely infested sites may therefore significantly reduce the serious losses that could be expected with Sitka spruce. In 14 out of 271 decayed Sitka spruce H. annosum was absent from the middle or base of the decay column but present at the top. Approximately 3% of infected spruce showed features suggesting some degree of resistance. Resin bleeding was observed at the base of 23.2% of the infected spruce, and the mean height of the decay column in these trees was significantly greater (0.96 m) than in those without this feature (0.66 m). The inoculum for infection was provided by stumps of the previous crop, and the genets of H. annosum that were present in some infected trees were also identified in stumps. The majority of infected trees contained only a single genet but three trees contained two genets. In this young crop individual genets were smaller than those found elsewhere; the largest extended to include six trees.     

Ants and birds reduce western spruce budworm feeding injury to small Douglas-fir and western larch in Montana

Western spruce budworm, Choristoneura occidentalis Freeman, larvae on small Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) and western larch (Larix occidentalis Nutt.) trees were protected from ant and bird predation during fourth instar to pupation. Significantly greater budworm densities were found on protected trees than on the controls at the end of the experiment, and significantly greater feeding injury was associated with increased budworm densities on fir. It is concluded that ants and birds remove budworm larvae feeding on small conifer trees and reduce injury up to 50%.     

Aerially applied methylcyclohexenone-releasing flakes protect Pseudotsuga menziesii stands from attack by Dendroctonus pseudotsugae

We tested methylcyclohexenone (MCH), an anti-aggregation pheromone for the Douglas-fir beetle (Dendroctonus pseudotsugae), for protection of Douglas-fir (Pseudotsuga menziesii) stands by applying MCH-releasing polymer flakes by helicopter twice during summer 2006 to five 4.05-ha plots in the State of Washington, USA. Five similar plots served as untreated controls. We assessed D. pseudotsugae flight into study plots using baited pheromone traps, and tallied D. pseudotsugae attack rates on all P. menziesii trees in 2005 and 2006. We also measured stand basal area and incorporated that as an explanatory variable in the analysis. Significantly fewer D. pseudotsugae were trapped in treated plots than in control plots, and significantly fewer P. menziesii trees were attacked in treated plots than in control plots. The attack rate in untreated stands was nearly 10 times that of treated plots, and stands with higher basal area were significantly more likely to be attacked by D. pseudotsugae than were stands of lower basal area. Attack rates in 2006 and 2005 were significantly correlated, regardless of treatment.     

Variation in the incidence and severity of drought crack in three conifer species in North East Scotland

The incidence of longitudinal drought cracks in coniferous trees may increase as a consequence of climate change. While larger diameter trees are more prone to splitting, it is unclear why only some of the larger trees within the same stand typically suffer damage. Matched pairs of trees of the same size with and without cracks were studied in two adjacent pole-stage mixed stands of Sitka spruce/grand fir (Picea sitchensis/Abies grandis) and Sitka spruce/noble fir (Picea sitchensis/Abies procera) located in North-East Scotland. A range of attributes were measured on 15 damaged and undamaged trees of each species. Length and position of cracks on stems were also recorded, and annual ring width and latewood percentage measured on cores. Noble fir had significantly longer cracks and these were located higher in the stem than the other species. Fewer cracks formed on east-facing side of stems in all species suggesting that prevailing westerly winds may place greater tensile forces on the damaged sides of stems. A higher proportion of latewood (associated with higher tangential shrinkage) was found in the firs and may explain the greater incidence of cracking on grand and noble fir stems (13% and 16%, respectively) in comparison with Sitka spruce (3%).     

Experimental release of a parasitoid, Doryctes yogoi Watanabe (Hymenoptera: Braconidae), onto Semanotus japonicus Lacordaire (Coleoptera: Cerambycidae) inoculated into live Japanese cedar trees (Cryptomeria japonica D.DON)

Release experiments of Doryctes yogoi Watanabe onto Semanotus japonicus Lacordaire larvae inoculated into Japanese cedar, Cryptomeria japonica D. Don, were conducted to clarify the role of the parasitoids in the mortality of S. japonicus and the efficiency of the parasitoid as a natural enemy of the beetle. S. japonicus larvae were inoculated into three types of samples: live trees, girdled trees, and logs, each of which was treated in three ways: D. yogoi was released into the sample, the sample was screened (excluding natural enemies), or the sample was used as a control. In live trees, more than 90% of the larvae were killed by resin flow, and the percentage of parasitism by D. yogoi was less than 6%. In girdled trees, most of the larvae were dead due to the resin in the trees, having survived inoculation as well as in live trees, but many larvae were parasitized by D. yogoi in dead trees like logs. The present study revealed three negative effects of resin flow on parasitism by D. yogoi in the live trees. First, most of the host larvae died before reaching a size suitable for parasitism. Second, parasitoid larvae were caught in the resin with their hosts and died. Third, the host-searching and oviposition of female D. yogoi were obstructed by resin flow on the surface of the trunk. The efficiency of D. yogoi as a natural enemy of S. japonicus is discussed.     

Effect of Betula pendula clone and leaf age on Melampsoridium betulinum rust infection in a field trial

Ten 5‐year‐old Betula pendula clones were studied for their rust resistance in the field. The trees were treated by inoculating 10 leaves on a shoot with Melampsoridium betulinum urediniospore suspension or spraying the control leaves with water. The birch clones differed significantly in their resistance to M. betulinum leaf rust fungus and the clones also varied in their responses to the local rust strain and the inoculated rust strains. However, natural rust infections and inoculation treatment were positively correlated. The older leaves had fewer infections than the younger ones on the tip of the shoot in the control trees, but in the inoculation treatment no significant correlation was found between the leaf ages and rust infection. The factors behind the different leaf susceptibilities are discussed.     

Effect of solid matrix priming during moist chilling on dormancy breakage and germination of seeds of four fir species

The ability of solid matrix priming (SMP) to overcome seed dormancy ofseeds of four fir species (Pacific silver fir, subalpine fir, grand fir andnoble fir), was examined. Seeds were subjected to treatments that combinedmoistchilling and SMP (SMP-chilling) and their germination compared to that elicitedby traditional moist chilling. For the SMP-chilling, six solid matrices withdifferent water holding capacities were tested (sphagnum, cat litter, peatmoss,Agro-Lig Greens Grade, Agro-Lig Micro Fine and sand). For each of the speciestested, germination performance was significantly improved by SMP-chilling; theresults were dependent on the type of solid matrix, the matrix water contentandthe treatment duration. SMP-chilling, using the best solid matrices for each ofthe species tested, resulted in germination percentages and rates that were24–35% and 8–21% higher, respectively, as compared with thatyieldedfrom control moist-chilling. High germination percentages (79% or greater) ofthree of the four species (Pacific silver fir, subalpine fir, and grand fir)were promoted after just four weeks (grand fir in sand) or eight weeks oftreatment (Pacific silver fir in peat moss and subalpine fir in Agro-Lig GreensGrade). The germination rate of grand fir seeds benefited from SMP-chillingperiods longer than four weeks, but this resulted in germination during thedormancy-breaking treatment. The water contents of the solid matrices that wereoptimal in terms of eliciting the best germination performance were 320% (w/w)for peat moss, 40% for Agro-Lig Greens Grade and 5–15% for sand.Conducting SMP at chilling temperatures (4 °C) is a practicalapproach to shorten the time required for effective dormancy termination ofAbies seeds; treatment times were shortened by 27 days forPacific silver fir and subalpine fir and more vigorous seedling growth wasexhibited by grand fir and noble fir.     

Oviposition preference and larval performance of Aeolesthes sarta (Coleoptera: Cerambycidae) in six hardwood tree species

Sarta longhorned beetle (SLB), Aeolesthes sarta Solsky, is an economically important pest of fruit and shade trees in central and east Asia. Choice, no-choice, and larval insertion experiments were conducted to determine SLB oviposition preference and larval host suitability on six hardwood tree species including Ulmus carpinifolia Borkh., Ulmus carpinifolia var. umbraculifera Rehd., Platanus orientalis L., Populus alba L., Salix alba L., and Fraxinus rotundifolia Miller subsp. persica (Boiss.), under laboratory conditions. In the choice and no-choice experiments, significantly greater numbers of eggs and living larvae, and greater mass of living larvae were found on U. carpinifolia and U. carpinifolia var. umbraculifera compared to those on the other tree species. In the choice experiment, oviposition did not occur on F. rotundifolia subsp. persica. There were a few eggs on P. alba but no living larvae. The mean mass of living larvae was lowest on P. orientalis. In addition, in the no-choice experiment significantly fewer numbers and mass of living larvae were found in P. alba and F. rotundifolia subsp. persica. In the larval insertion experiment, more larvae survived on U. carpinifolia and U. carpinifolia var. umbraculifera compared to the other trees. Larvae recovered from U. carpinifolia and U. carpinifolia var. umbraculifera weighed significantly more than larvae from the other trees. These results suggest that U. carpinifolia and U. carpinifolia var. umbraculifera are the most preferred and suitable hosts for SLB adults and larvae. Salix alba is an acceptable host for adult oviposition and a potentially suitable host for larval development. Platanus orientalis and P. alba are less suitable, and F. rotundifolia subsp. persica appeared to be unsuitable as a host for SLB.     

Tree spatial patterns of Abies alba and Fagus sylvatica in the Western Carpathians over 30 years

The decline of Abies alba (fir) in natural fir–beech forests in Europe has fascinated scientists for over a century. During this period, Fagus sylvatica (beech) became the dominant species in this forest type. We hypothesised that (1) the success of beech over fir is significantly connected with the fact that beech suffers less than fir from the presence of conspecific neighbours; that (2) shade tolerance is not a factor which favours beech over fir; and that (3) this is due to a significantly reduced proportion of litter treethrow mounds with suitable conditions for the successful regeneration of fir. We investigated these hypotheses by means of tree spatial pattern analysis. Eight rectangular plots (2–8 ha) were analysed in mountain fir–beech forests of the Outer Western Carpathians, Czech Republic. Various types of the pair correlation function and L function were used to describe the tree density variability of trees with DBH ≥10 cm. The analyses were carried out on datasets from the 1970s, 1990s and 2000s. Our results suggest that negative density dependence is not responsible for the current decline of fir. It seems that a higher shade tolerance of the advanced regeneration could be one of the factors which favour beech over fir. It is evident that fir trees have a markedly stronger positive association to mounds than beech trees.     

Effects of defoliation by Eucalyptus weevil, Gonipterus scutellatus, and chrysomelid beetles on growth of Eucalyptus globulus in southwestern Australia

Plantations of Eucalyptus globulus in southwestern Australia are defoliated by Eucalyptus weevil, Gonipterus scutellatus, and a complex of chrysomelid and scarab beetles, yet there is no information on the impact of beetle defoliation to tree growth in southwestern Australia. To address this shortcoming, we used insect exclusion trials, to compare growth of insecticide treated (and thus relatively undamaged) trees with untreated (and thus defoliated) trees to determine whether defoliation by G. scutellatus and other beetles reduced the growth and harvest volume of E. globulus trees. Our results showed some evidence of beetle defoliation reducing growth of E. globulus. Mean defoliation levels of the growing tip of untreated trees ranged from 18% to 33% across the duration of the study and were significantly greater than mean defoliation levels of 5–16% on insecticide treated trees. Seasonal peaks in defoliation of 30–80% to the growing tip of untreated trees were recorded between late spring and early autumn. The greatest impact of defoliation on tree growth was evident during the 2.5 year period of insect exclusion, when higher relative growth rates were recorded for insecticide treated trees, which were significantly different from relative growth rates of untreated trees at two of the four plantations. However, our results showed only a limited impact of beetle defoliation on the total volume at harvest. Initially small trees tended to suffer more severe defoliation than initially large trees. Effects of insect exclusion treatment on harvest volume were modified by the initial tree size and the relationship between the initial tree size and levels of defoliation.     

Lesion formation and host response to infection by Armillaria ostoyae in the roots of western larch and Douglas‐fir

The process of lesion formation and host response to natural infection by Armillaria ostoyae were studied in the roots of western larch (Larix occidentalis) and Douglas‐fir (Pseudotsuga menziesii ssp. glauca) trees in the three age classes, 6–8, 18–19 and 85–95 years. The characteristics of lesions on infected roots were recorded and bark samples were dissected from infection points and lesion margins in the field and stored in liquid nitrogen for macroscopic study in the laboratory. Infection in the roots of 6‐ to 8‐year‐old trees advanced freely, overcoming any host resistance, quickly girdling the root collar and killing the trees. In 18‐ and 19‐year‐old trees, however, 43% of infections on western larch and 27% of the infections on Douglas‐fir roots were confined to lesions bounded by necrophylactic periderms with multiple bands of phellem. Host response was similar in 85‐ to 95‐year‐old trees, but the percentage of confined lesions was higher than in younger trees. The results suggest that larch shows resistance to A. ostoyae at a younger age and with greater frequency than Douglas‐fir.     

Timber product output implications of a program of mechanical fuel treatments applied on public timberland in the Western United States

This study reports the results from a 5 year simulation of forest thinning intended to reduce fire hazard on publicly managed lands in the western United States. A state simulation model of interrelated timber markets was used to evaluate the timber product outputs. Approximately 84 million acres (34 million hectares), or 66% of total timberland in the western United States, is publicly managed; of this 78 million acres (31.6 million hectares) are managed by the federal agencies. We considered three budget scenarios using a least-expensive highest-hazard area first policy. Our intention with this simulation is not to definitively answer questions about where or how to conduct treatments to reduce fire hazard on public lands but rather to begin to develop tools that can be used to inform such a policy debate. Considerable development of this tool is still needed before it will be useful for that purpose. Our initial simulations nonetheless provide insight into what might happen if available funds were allocated to the least-expensive highest-hazard areas across the west. Using assumptions of (1) an annual “subsidy” (payments for treatments), (2) the treatment costs, (3) the priority ranking by forest type, (4) fire hazard level, and (5) the wildland–urban interface (WUI) status, the simulation suggests that lodgepole pine (Pinus contorta), ponderosa pine (Pinus ponderosa), spruce (Picea spp.)–fir (Abies spp.) and Douglas-fir (Pseudotsuga menziesii) are projected to be major forest types treated in the West. A combination of our treatment ranking assumptions and the low total treatable WUI acres on public timberland caused the model to concentrate almost exclusively on all the WUI stands and non-WUI ponderosa pine forest type at the budget of $150 million and $300 million. With the further increase of budget, a large proportion of treated acres are lodgepole pine and spruce–fir forest types using the thin-from-below approach. About 41% of the volume removals are sawtimber for all the public timberland treated under the low budget scenario ($150 million/year), 58 for moderate budget ($300 million/year), 50 for the high budget scenario ($1500 million/year). Under the moderate budget case ($300 million a year), about 19% of the total wood removed is projected to come from trees less than 5-inches (12.7 cm) in diameter at breast height (dbh), and another 16% of the biomass is expected from trees 20-inches (50.8 cm) dbh and above.     

Über kombinierte Wirkungen eines Juvenoids (Altosid) und eines Bacillus-thuringiensis-Präparats (Bactimos) auf Larven der Stechmücken Culex pipiens molestus Forsk. und Theobaldia longiareolata Macq. (Dipt., Culicidae)

Exposing second and fourth instar larvae ofCulex pipiens molestus for 24 h to Altosid increased their tolerance to Bactimos. The interaction was apparent in fourth instar larvae treatment especially at the higher concentrations. Exposure bactimos to Altosid for 72 hours decreased its efficacy against the fourth instar larvae ofCulex pipiens molestus. The LT₅₀ values were significantly lower in larvae treated with Bactimos only than that treated with Altosid and Bactimos. Altosid briquets increased significantly the tolerance ofTheobaldia longiareolata larvae toBacillus thuringiensis var.israelensis at all concentrations tested. Generally, pretreatment mosquito larvae with Altosid followed by Bactimos, increased the tolerance of larvae to the bacterium, this may be due to the toxic effect of Altosid on the bacterium or to the changes in the physiological status of the treated larvae to tolerate the effect of bacterium. On the light of these studies, Altosid exhibited detrimental effect on the efficacy ofB. thuringiensis var.israelensis againstC. pipiens molestus andT. longiareolata larvae. Therefore, interactions between Altosid and Bactimos could not fit the integrated control of mosquitoes.     

The effect of the game deterrent Wöbra on attacks by the poplar clearwing moth,Paranthrene tabaniformis Rott. (Lep., Sesiidae)

The game deterrent “Wöbra”, a copolymer containing quartz sand, is smeared on trees to deter mammals from damaging the bark. An experiment showed that Wöbra might act as a physical barrier against woodboring insects but it did not prevent infestations by larvae ofParanthrene tabaniformis (Lep.; Sesiidae) in one-year-old poplars. Wöbra had not adversely affected the annual height increment of the treated trees up to three years after application.     

The impact of forest fertilization on growth of mature Norway spruce affected by Sirococcus shoot blight

The effects of forest fertilization and Sirococcus shoot blight on growth of mature Norway spruce (Picea abies (L.) Karst.) were studied in a field experiment. The single tree fertilization experiment was established with 144 sample trees in the year 2000. These trees were selected among the dominant and co-dominant trees of the stand in a way that half of the trees exhibited symptoms of Sirococcus shoot blight and the other half did not. One-third of the sample trees were fertilized with dolomitic lime, one-third with kieserite and gypsum and one-third were left unfertilized as control. The treatments were randomly assigned to the sample trees. As the experimental design became unbalanced due to tree mortality caused by bark beetle infestation final analyses were performed with the volume growth data of 125 sample trees only. An analysis of covariance was used to evaluate the effect of fertilization and Sirococcus shoot blight on volume growth. The average volume increment of the period 1977–1980 was used as a covariate attribute, assuming that during this period growth was not yet affected by Sirococcus shoot blight. Indeed an effect of Sirococcus shoot blight on growth turned out to start after 1980 and the analysis revealed that over the whole period 1981–2006 trees with shoot blight symptoms had a significantly lower increment. The increment reduction of the nonfertilized trees by Sirococcus   was 7.46±2.90$7.46\pm 2.90$% in 1981 and was continuously increasing with time to 37±3.78$37\pm 3.78$% by the year 2000. A significant positive effect of fertilization was only found for the kieserite+gypsum$\text{kieserite}+\text{gypsum}$ variant from 2002 to 2006, with the highest surplus increment in 2004 with 31.6±15.2$31.6\pm 15.2$%, calculated as average over the diseased and healthy group. However, a mitigation of the Sirococcus-caused increment loss via fertilization with kieserite and gypsum was statistically significant only for the year 2003. A moderate relationship between basal area increment and disease severity was found, indicating decreasing basal area increment with increasing disease severity.     

Evaluation of nine strains ofBacillus thuringiensis Berliner against the giant looper,Boarmia (Ascotis) selenaria Schiffermüller (Lepidoptera,Geometridae)

Nine isolates ofBacillus thuringiensis Berliner belonging to var.kenyae, var.aizawai and var.entomocidus, were bioassayed against 1st instar larvae ofBoarmia (Ascotis) selenaria Schiffermüller and compared withB. thuringiensis var.kurstaki, HD-1-S-1980. None were found to have a higher potency than HD-1-S-1980, which is used for commercial control of young larvae of this pest in avocado plantations in Israel.     

Availability of standing trees for large cavity-nesting birds in the eastern boreal forest of Québec,Canada

Large cavity-nesting birds depend on large-diameter trees for suitable nest sites. The increased spatial extent of commercial timber harvesting is modifying forest structure across the land base and may thus compromise the availability of large trees at the landscape scale. In this study, our objectives were to (1) characterize the availability of large living and dead trees in old-growth stands dominated by different tree species and surficial deposits that encompass the range of natural cover types of eastern Québec's boreal forest; (2) analyze the distribution of trees among decay-classes; and (3) compare the availability of large trees in unharvested, remnant, and harvested stands for the entire range of decay-classes. A total of 116 line transects were distributed across unharvested forests, remnant linear forests, and cutblocks in cutover areas. Unharvested forest stands (black spruce [Picea mariana], balsam fir [Abies balsamea]–black spruce, balsam fir–white spruce [Picea glauca] and balsam fir) reflected a gradient of balsam fir dominance. The remnant forests selected were isolated for 5–15 years. Analyses were performed at two diameter cut-off values. Trees with DBH ≥20 cm were considered for availability of total trees whereas trees with DBH ≥30 cm were considered for availability of large trees. Forest stands comprised high proportions of standing dead trees (33% of all stems, 8% were large dead stems). Availability of total and large standing trees increased with the dominance of balsam fir in stands. Forest stands located on thick surficial deposits showed higher densities of large dead trees for every stand type suggesting a higher productivity on those sites. Availability of stems according to decay-classes showed a dome-shaped distribution with higher densities of snags in intermediate decay stages. However, for large stems, black spruce stands showed a significantly lower availability that was consistent across all decay-classes. In linear remnant forests, pure balsam fir stands were absent. Remnant stands thus showed a much lower availability in large trees when compared with unharvested balsam fir stands. Clearcuts had the lowest densities of dead trees across sampled stands. Current even-aged management practices clearly affect availability and recruitment of large trees, therefore forest-dwelling wildlife relying on these structures for breeding is likely to be affected by large-scale harvesting in coniferous boreal forests.     

Does tree seedling growth and survival require weeding of Himalayan balsam (Impatiens glandulifera)?

The effect of Himalayan balsam (Impatiens glandulifera) on survival and growth of naturally regenerated silver birch (Betula pendula) and planted Norway spruce (Picea abies) and silver fir (Abies alba) seedlings was studied in a weeding experiment over 3 years. Three different treatments were applied: control, mowing, and hand weeding by pulling out the entire plant. There were no consistent treatment effects on height and diameter of the tree seedlings. The coverage of Rubus fruticosus had a negative impact on diameter increment of Norway spruce and silver fir. As opposed to growth, treatment effects on seedling survival could be found for planted Norway spruce and silver fir. However, it is very likely that these effects, namely higher seedling survival after mowing, have to be attributed to the control of bramble (Rubus fruticosus) rather than to that of Himalayan balsam. It is concluded that Himalayan balsam is not able to seriously affect the growth of already established seedlings.     

Growth reduction in harvest-age,coniferous forests with residual trees in the western central Cascade Range of Oregon

To evaluate the relationship of overstory residual trees to the growth of unmanaged young-to-mature understory Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and western hemlock (Tsuga heterophylla (Raf.) Sarg.), the basal area and volume of 14 paired plots with and without residual trees were examined in the Willamette National Forest, Oregon. Residual trees were large survivors of the fires that initiated the understory between 55 and 121 yr ago. Understory stands were naturally regenerated and not managed in any way. High residual tree and understory densities were negatively associated with understory volume. The relation of density of residual trees to total understory and Douglas-fir basal areas and volumes was best described by a negative logarithmic function. The rate of decrease in total understory and Douglas-fir basal areas and volumes per individual residual tree became smaller with increasing residual-tree density. Predicted total understory volume reduction was 23% with five residual trees/ha and 47% with 50 residual trees/ha, averaging 4.6% and 0.9% per residual tree, respectively. After including the estimated volume growth of residual trees since initiation of the understory, stand volume was still 19% lower with five residual trees/ha and 41% lower with 50 residual trees/ha than in stands with no residual trees, averaging a reduction of 38% and 0.8% per residual tree, respectively. In mixed stands of Douglas fir and western hemlock, predicted Douglas-fir basal area and volume declined more rapidly than did total understory basal area and volume when residual-tree densities exceeded about 15 trees/ha. This difference was probably due to the relative shade-intolerance of Douglas fir. Predicted Douglas-fir volume reduction was 13% with five residual trees/ha and 75% with 50 residual trees/ha, averaging 2.6% and 1.5% per residual tree, respectively. The southern aspects had more than 150% the total understory basal area and volume and more than 200% the Douglas-fir volume and basal area of the northern aspects. Lower density and basal area of understory trees, particularly of dominant and codominant Douglas fir, were associated with increasing residual-tree densities. Given the same diameter at breast height (DBH), heights of Douglas fir were not related to residual trees. Regardless of understory age, understory volume was greatest in stands with the lowest understory densities. These results suggest that timber production in unthinned green-tree retention units may be reduced and may depend on the density of leave-trees. Thinning of understory trees is recommended to reduce growth loss from intraspecific competition.     

Protection of spruce from colonization by the bark beetle, Ips perturbatus, in Alaska

Field bioassays were conducted in south-central Alaska in a stand of Lutz spruce, Picea × lutzii, to determine whether a semiochemical interruptant (verbenone and trans-conophthorin) and/or a defense-inducing plant hormone (methyl jasmonate, MJ) could be used to protect individual standing trees from bark beetle attack. During two experiments (initiated in May 2004 and 2005, respectively), attacks by Ips perturbatus on standing trees were induced by using a three-component aggregation pheromone (ipsenol, cis-verbenol, and ipsdienol) and prevented by using the interruptant. In 2005, treatments from 2004 were repeated and additional treatments were evaluated by using MJ spray or injection with and without the interruptant. Aggregation began before 3 or 7 June, and attack density was monitored through 3 or 16 August. During both years, tree mortality caused by I. perturbatus was recorded twice (in August, and in May of the following year). In both experiments, attack density was greatest on trees baited with the three-component attractive pheromone, but was significantly reduced by addition of the semiochemical interruptant to trees baited with the attractant. There were no significant differences in attack density between attractant + interruptant-treated trees and unbaited trees. In 2004, mortality was highest among attractant-baited trees, whereas addition of the interruptant significantly reduced the level of initial (10 week post-treatment) and final (54 week post-treatment) mortality. In 2005, no significant reduction in attack density occurred on trees baited with the attractant when MJ was sprayed or injected. The highest initial (10.6 week post-treatment) and final (49.4 week post-treatment) mortality was observed among trees that had been injected with MJ and baited with the attractant. Mortality at the final assessment was significantly lower in all other treatment groups. As in 2004, addition of the interruptant to attractant-baited trees significantly reduced the level of final mortality compared to attractant-baited trees. MJ was not attractive or interruptive to I. perturbatus or associated bark beetles in a flight trapping study. However, MJ-treated trees (sprayed or injected) exuded copious amounts of resin on the bark surface. Anatomical analyses of felled trees from four treatment groups [Tween (solvent)-sprayed, MJ-sprayed, Tween-injected, and MJ-injected + attractant baited] showed that treatment with MJ increased the number and size of resin ducts produced following treatment. These analyses also revealed a reduction in radial growth in MJ-treated trees. Our results show that during both years, treatment with a simple, two-component interruptant system of verbenone and trans-conophthorin significantly reduced I. perturbatus attack density and tree mortality on attractant-baited trees and provided a full year of protection from bark beetle attack.