Pine Shoot Research Articles

Phylogeography of the Eurasian pine shoot beetle Tomicus piniperda (Coleoptera: Scolytidae)

Tomicus piniperda is a pest in pine stands in Eurasia and is also found in the USA, where it has caused a decline in the abundance of pine since 1992. Knowledge of the genetic structure of pine shoot beetle populations is important for understanding their phylogeographic history and for quarantine control. In this study, European, Asian and American T. piniperda populations were analyzed by sequencing a region of the mitochondrial COI gene. Twenty-five haplotypes (HT) were detected and over 70% of these HT were found in individual areas, e.g. 5 HT in China, 5 HT in France and 3 HT in Spain. Nested clade analysis revealed that most European and the American population was in a clade containing 9 HT connected by one to two mutational steps. A second clade contained HT from France (2 HT), Spain (2 HT), Sweden (1 HT), Russia (1 HT) and China (5 HT). In this clade, one to 13 mutational steps and 13 missing or theoretical HT were detected. The third clade had 5 HT from France, Russia, Poland, Finland and Switzerland; 1 to 7 mutational steps and 5 missing or theoretical HT were detected. Although only a few significant relationships were found in the nested clade analysis, the following conclusions can be drawn: (1) T. piniperda is a polymorphic species with numerous HT throughout Europe, and HT are likely to exist regarding the missing or theoretical HT; (2) It is likely there were refugial areas in Southern Europe and Western Russia; (3) The Pyrenees formed a barrier to migration after the last ice age; (4) Chinese and European populations have been separated for at least 0.6 MYA.

Root induction in radiata pine using Agrobacterium rhizogenes

Root induction using Agrobacterium rhizogenes was conducted in hypocotyl explants, intact seedlings, de-rooted seedling cuttings and adventitious shoots of radiata pine ( Pinus radiata D. Don). Use of two A. rhizogenes strains (A4T and LB9402), with or without application of IBA, can trigger root formation in different explants. Strain LBA9402 was more effective than A4T in increasing rooting percentage and root number. Addition of 4.4 uMIBA to the medium further enhanced rooting from the cultured hypocotyl segments inoculated with the two A. rhizogenes strains. Strain LBA9402+IBA induced in about 75% of the cultured hypocotyl segments to form roots. In contrast the controls failed to initiate roots on intact seedlings or cultured segments in presence or absence of IBA. Rooting of adventitious shoots from 3 year-old radiata pine was improved following inoculation with LBA9402, suggesting that this rooting treatment has potential to aid clonal propagation of radiata pine.

Root induction in radiata pine using Agrobacterium rhizogenes

Root induction using Agrobacterium rhizogenes was conducted in hypocotyl explants, intact seedlings, de-rooted seedling cuttings and adventitious shoots of radiata pine ( Pinus radiata D. Don). Use of two A. rhizogenes strains (A4T and LB9402), with or without application of IBA, can trigger root formation in different explants. Strain LBA9402 was more effective than A4T in increasing rooting percentage and root number. Addition of 4.4 uMIBA to the medium further enhanced rooting from the cultured hypocotyl segments inoculated with the two A. rhizogenes strains. Strain LBA9402+IBA induced in about 75% of the cultured hypocotyl segments to form roots. In contrast the controls failed to initiate roots on intact seedlings or cultured segments in presence or absence of IBA. Rooting of adventitious shoots from 3 year-old radiata pine was improved following inoculation with LBA9402, suggesting that this rooting treatment has potential to aid clonal propagation of radiata pine.

The Canadian Phytopathological Society Annual Meeting, Montréal, Quebec, 2003

The Canadian Phytopathological Society Annual Meeting, Montréal, Quebec, 2003

Detection of Latent Sphaeropsis sapinea Infections in Austrian Pine Tissues Using Nested-Polymerase Chain Reaction

ABSTRACT Sphaeropsis sapinea is the causal agent of Sphaeropsis tip blight disease of pines. Past surveys of diseased and symptomless Austrian and Scots pines revealed that latent infections of symptomless shoots by S. sapinea are common. The role of these latent infections in the tip blight disease is unknown. A sampling technique and nested-polymerase chain reaction (PCR) protocol were developed to detect latent S. sapinea in symptomless pine shoots. The sampling protocol was designed to be minimally destructive to the shoot so it could be preserved for further studies. The primers that were developed were specific for S. sapinea DNA and did not amplify DNA from any of 13 other endophytic fungal species that were commonly isolated from symptomless pine shoots. The PCR primers also amplified DNA of Botryosphaeria obtusa, which was, however, rare in symptomless Austrian pine tissues. The protocol detected as little as 0.93 pg of S. sapinea DNA in terminal bud samples and 10.4 pg of DNA in bark samples. Correlation (chi-square) analyses indicated that the nested-PCR protocol detected latent S. sapinea infections in both bud and bark samples with an efficiency that was statistically equivalent to isolating the fungus from the tissue. The nested-PCR protocol will make it possible to more quickly identify latent S. sapinea infections in symptomless pine shoots and should be useful in future studies of the latency phenomenon.

Colonization of Scots, red, and jack pine logs by Tomicus piniperda (Coleoptera: Scolytidae) in Michigan pine stands

We investigated host preference of the pine shoot beetle, Tomicus piniperda (L.) (Coleoptera: Scolytidae), in a large-scale field study in 1997 and 1998. This Eurasian pest, first discovered in North America in 1992, is capable of developing and shoot-feeding in many North American pines. We hypothesized, however, that T. piniperda would preferentially colonize Scots pine (Pinus sylvestris L.), a Eurasian species, more frequently than North American red pine (Pinus resinosa Ait.) and jack pine (Pinus banksiana Lamb.). We placed freshly cut Scots, red, and jack pine logs in Scots, red, and jack pine forest stands each year in southwestern Michigan, where T. piniperda populations have been established for several years, and in central and northern Michigan, where T. piniperda populations were low to rare. Following T. piniperda progeny emergence, logs were retrieved and debarked and T. piniperda attack density was determined for each log. Tomicus piniperda colonized 80%–90% of the pine logs in the southwestern Michigan stands compared with 2%–19% of logs in the central Michigan stands. No logs in the northern Michigan stands were colonized by T. piniperda in either year. In the southwestern pine stands, T. piniperda attack densities were significantly greater on Scots pine logs than on jack and red pine logs, regardless of stand species.

Development of an improved attractive lure for the pine shoot beetle, Tomicus piniperda (Coleoptera: Scolytidae)

Abstract 1 The pine shoot beetle, Tomicus piniperda (L.) (Coleoptera: Scolytidae), is an exotic pest of pine, Pinus spp., and was first discovered in North America in 1992.2 Although primary attraction to host volatiles has been clearly demonstrated for T. piniperda, the existence and role of secondary attraction to insect‐produced pheromones have been widely debated.3 Currently, commercial lures for T. piniperda include only the host volatiles α‐pinene in North America and α‐pinene, terpinolene and (+)‐3‐carene in Europe. Several potential pheromone candidates have been identified for T. piniperda.4 We tested various combinations of host volatiles and pheromone candidates in Michigan, U.S.A., and Ontario, Canada, to determine an optimal blend.5 Attraction of T. piniperda was significantly increased when trans‐verbenol (95% pure, 3.2%cis‐verbenol content) was added with or without myrtenol to α‐pinene or to blends of α‐pinene and other kairomones and pheromone candidates.6 Our results, together with other research demonstrating that trans‐verbenol is produced by T. piniperda, support the designation of trans‐verbenol as a pheromone for T. piniperda. A simple operational lure consisting of α‐pinene and trans‐verbenol is recommended for optimal attraction of T. piniperda.

Nantucket Pine Tip Moth Development and Population Dynamics: Influence of Nitrogen Fertilization and Vegetation Control

Abstract It is commonly believed that Nantucket pine tip moth (Rhyacionia frustrana [Comstock]) feeding damage on loblolly pine (Pinus taeda L.) increases in relation to the intensity of silvicultural practices. Some studies have produced contrary or inconclusive data regarding this issue. This study was designed to examine the relationships between tree growth rates and tip moth development by enhancing growth with nitrogen (N) fertilizer and herbicide applications. The four treatments were N fertilizer, herbicide, herbicide+fertilizer, and untreated control. These treatments were monitored for tip moth damage levels, tip moth pupal numbers per pine shoot, insect population dynamics, and tree growth. Pine growth was significantly greater in the herbicide treatments than in the other treatments. There was a significant increase in diameter related to the fertilizer treatments, but no differences in tree height or volume were detected. Pupal weight was significantly lower in the herbicide treatment in the second year. Tip moth population fluctuations were greater in the herbicide treated plots than in the untreated control, and there were significant linear relationships between these fluctuations in the treatments versus percent parasitism, pupal weight, and diameter growth. This study shows that tip moth populations are not necessarily increased or decreased by intensive management practices, but can be less stable due to these practices.

Infection of Tomicus piniperda (Col., Scolytidae) with Canningia tomici sp. n. (Microsporidia, Unikaryonidae)

Abstract Canningia tomici sp. n. (Microsporidia, Unikaryonidae) infects the midgut epithelium, the gut muscules, Malpighian tubules, connective tissues, adipose tissues and the gonads of the pine shoot beetle, Tomicus piniperda (L.) (Coleoptera, Scolytidae). The infection is present in populations of Tomicus piniperda in Europe and in the United States. Uninucleate oval single spores occur in two sizes: 2.8 ± 0.4 × 1.4 ± 0.4 μm and 3.8 ± 0.3 × 2.0 ± 0.2 μm. The polar filament of this microsporidium is fixed subapically in a flat anchoring disc. The thick posterior lamellae of the binary polaroplast are asymmetric due to the lateral fixation of the polar filament.

Seasonal variation in respiration of 1-year-old shoots of scots pine exposed to elevated carbon dioxide and temperature for 4 years.

Sixteen 20-year-old Scots pine (Pinus sylvestris L.) trees growing in the field were enclosed for 4 years in environment-controlled chambers that maintained: (1) ambient conditions (CON); (2) elevated atmospheric CO2 concentration (ambient + 350 micro mol mol-1; EC); (3) elevated temperature (ambient +2-6 degrees C; ET); or (4) elevated CO2 and elevated temperature (ECT). The dark respiration rates of 1-year-old shoots, from which needles had been partly removed, were measured over the growing season in the fourth year. In all treatments, the temperature coefficient of respiration, Q10, changed with season, being smaller during the growing season than at other times. Respiration rate varied diurnally and seasonally with temperature, being highest around mid-summer and declining gradually thereafter. When measurements were made at the temperature of the chamber, respiration rates were reduced by the EC treatment relative to CON, but were increased by ET and ECT treatments. However, respiration rates at a reference temperature of 15 degrees C were reduced by ET and ECT treatments, reflecting a decreased capacity for respiration at warmer temperatures (negative acclimation). The interaction between season and treatment was not significant. Growth respiration did not differ between treatments, but maintenance respiration did, and the differences in mean daily respiration rate between the treatments were attributable to the maintenance component. We conclude that maintenance respiration should be considered when modelling respiratory responses to elevated CO2 and elevated temperature, and that increased atmospheric temperature is more important than increasing CO2 when assessing the carbon budget of pine forests under conditions of climate change.

Attraction of Hylastes opacus (Coleoptera: Scolytidae) to nonanal

Hylastes opacus Erichson is a recently introduced bark beetle in North America (Bright and Skidmore 1997; Hoebeke 1994; Rabaglia and Cavey 1994; Wood 1992). It is widely distributed in the Palearctic region, where it usually breeds in stumps and roots of dead or dying pines (Pinus) and occasionally other conifers (Hoebeke 1994). Like many species of bark beetles, H. opacus uses host volatiles as cues to search for suitable host material for feeding and establishment of broods. Hoebeke (1994) reported the attraction of H. opacus to ethanol-baited logs of Scots pine (Pinus sylvestris L.) and red pine (Pinus resinosa Ait.) in New York, United States of America. In Sweden, Schroeder and Lindelöw (1989) observed H. opacus responding to (−)-α-pinene and to ethanol released separately, but a synergistic increase in response did not occur when these two compounds were released together. In later experiments, Lindelöw et al. (1993) found that traps baited with ethanol alone, ethanol + (−)-α-pinene, and spruce turpentine caught significantly more H. opacus than unbaited traps. In these experiments, (−)-α-pinene alone was not attractive, and when (−)-α-pinene was combined with spruce turpentine and ethanol, it reduced catches of H. opacus. In 2002, while investigating attractants for the pine shoot beetle, Tomicus piniperda (L.) (TM Poland, P de Groot, S Burke, D Wakarchuk, RA Haack, and RW Nott, unpublished data), we unexpectedly found significant numbers of H. opacus in one of our experiments. Here we report that H. opacus is strongly attracted to nonanal.

Association of Sphaeropsis sapinea with insect‐damaged red pine shoots and cones

SummaryThe association of the shoot blight and canker pathogen Sphaeropsis sapinea with red pine (Pinus resinosa) shoots and cones damaged by insects (especially Dioryctria sp.) was investigated. Samples from a single plantation approximately 35 years old, in Sauk Co., Wisconsin and also from three plantations, between approximately 40 and 50 years old, located in an area of pine shoot moth activity in the preceding year in Adams Co., Wisconsin were visually examined. Samples were arbitrarily collected from trees felled in the first plantation in May. Pycnidia of S. sapinea and insect damage were observed on 56 of 91 (62%) of closed cones and 17 of 165 (7%) of previous year's shoots. In the absence of insect damage, pycnidia of the pathogen were identified only on eight of 91 (9%) closed cones and never on previous year's shoots. In each of the other three plantations, 10 trees were located at intervals along transects in mid‐June; one branch from the lower half of the crown per tree was pruned off, and both current and previous year's shoots were examined. Insect damage and S. sapinea pycnidia were too rare on current year's shoots to draw any conclusions. Insect damage occurred on 20–40% of over 2000 previous year's shoots that were examined, but pycnidia of the pathogen were identified on only about 5%. Although infrequent, S. sapinea was identified in association with insect‐damaged previous year's shoots from these three plantations three times more frequently than those without insect damage. Random amplified polymorphic DNA (RAPD) markers from eight randomly selected isolates were consistent with the A group of S. sapinea, which can be aggressive on red pine. This ability to exploit insect‐damaged shoots may facilitate long‐term persistence of S. sapinea at low disease incidence and severity. The potential role of insect wounds as infection courts and insects as vectors of this important pathogen of pines deserves further study.

Effects of exogenous gibberellin and auxin on shoot elongation and vegetative bud development in seedlings of Pinus sylvestris and Picea glauca.

The hormonal control of stem unit (foliar appendage and axillary structure, if present, plus subtending internode) number and length was investigated in shoots of Scots pine (Pinus sylvestris L.) and white spruce (Picea glauca (Moench) Voss). Seedlings were treated with six gibberellins (GA1, GA3, GA4, GA5, GA9 and GA20) and two auxins (indole-3-acetic acid (IAA) and naphthaleneacetic acid (NAA)) when either neoformed growth was occurring or the terminal vegetative bud was developing. Hormones were applied by drenching the shoot tip, injecting the stem or spraying the foliage. Combined results for all three application methods indicated that shoot elongation in first-year seedlings (i.e., neoformed growth) was promoted in both species by GA1, GA3, GA4 and, less obviously, by GA9. This promotion was attributable to an increase in length, rather than number, of stem units. However, the number of stem units formed during terminal bud development, as reflected in the number of needles (white spruce) or cataphylls (Scots pine) present on the shoot resulting from the terminal bud, was stimulated by GA1, GA3 and GA4 in both species and by GA9 in Scots pine. The GA-induced increase in the number of preformed stem units was associated with increased bud width in white spruce and increased bud length and resulting shoot length in Scots pine. In contrast, application of IAA or NAA either did not affect or inhibited both neoformed growth and terminal bud stem unit number, depending on the application method and concentration. We conclude that, in the Pinaceae, (1) GA stimulates the activity of both the subapical meristem during neoformed growth and the apical meristem during vegetative bud development, and (2) the early non-hydroxylation pathway, via GA9, is the major route of GA biosynthesis. The role of auxin in the control of stem unit number and length remains to be resolved.

Annual pattern of photosynthesis in Scots pine in the boreal zone.

To detect seasonal changes in photosynthetic rate in the field, a set of 18,000 photosynthetic measurements made between April and October on three shoots of Scots pine growing near the northern timberline was studied. The measurements were analyzed in the framework of an optimal stomatal control model of photosynthesis, in which irradiance (photosynthetically active radiation, I), air humidity and ambient temperature are driving variables. All driving variables were monitored concomitantly with gas exchange measurements throughout the growing season. The model has nine parameters, of which six were assumed to be constant over the growing season and were fixed based on previous information. The three variable parameters were the initial slope (alpha) and saturation value (gamma) of the light-response curve of carboxylation efficiency in the intercellular cavity, and the cost of transpiration (lambda), in carbon units, regulating the degree of stomatal opening. These parameters could not be estimated independently, nor could their values be satisfactorily found by standard nonlinear regression techniques. A Monte Carlo based simulation procedure was devised to analyze the best-fit parameters and their mutual correlations near the minimum of the residual sum of squares. This was accomplished by replacing the saturation value of the light-response curve with a linearity parameter that determined the shape of the curve. In the best fit solutions, only alpha and lambda varied from day to day, whereas the shape of the curve was constant (i.e., gamma was proportional to alpha). Both alpha and lambda showed consistent patterns from spring to autumn, but the seasonal variation was considerably greater for alpha than for lambda. The optimal stomatal control model with the seven fixed and two daily parameter values gave a good overall fit for photosynthetic rate over the season (PEV > 95%).

Relations between Scots pine needle element concentrations and decreased needle longevity along pollution gradients

Scots pine ( Pinus sylvestris L.) shoots were sampled along transects near one urban pollution source and two smelters. Needle Mg, P and K concentrations decreased from the second to the fourth age class linearly with needle survival along the urban pollution gradient. Still, over 80% of the average concentration of these nutrients remained in the fourth needle age class. Decreased needle longevity was closely related to the increased heavy metal concentrations near the smelters. Near the urban pollution source, it was related to the increased annual needle mass and the increased needle nutrient concentrations. Decreased Mn accumulation along with needle age was detected near all pollution sources. Leaching of Mn from needles and especially from soil as a cause of decreased needle concentrations is discussed.

Xylem vulnerability to cavitation in Pseudotsuga menziesii and Pinus ponderosa from contrasting habitats.

In the Rocky Mountains, ponderosa pine (Pinus ponderosa (ssp.) ponderosa Dougl. ex P. Laws. & C. Laws) often co-occurs with Douglas-fir (Pseudotsuga menziesii var. glauca (Mayr) Franco). Despite previous reports showing higher shoot vulnerability to water-stress-induced cavitation in ponderosa pine, this species extends into drier habitats than Douglas-fir. We examined: (1) whether roots and shoots of ponderosa pine in riparian and slope habitats are more vulnerable to water-stress-induced cavitation than those of Douglas-fir; (2) whether species-specific differences in vulnerability translate into differences in specific conductivity in the field; and (3) whether the ability of ponderosa pine to extend into drier sites is a result of (a) greater plasticity in hydraulic properties or (b) functional or structural adjustments. Roots and shoots of ponderosa pine were significantly more vulnerable to water-stress-induced cavitation (overall mean cavitation pressure, Psi(50%) +/- SE = -3.11 +/- 0.32 MPa for shoots and -0.99 +/- 0.16 MPa for roots) than those of Douglas-fir (Psi(50%) +/- SE = -4.83 +/- 0.40 MPa for shoots and -2.12 +/- 0.35 MPa for roots). However, shoot specific conductivity did not differ between species in the field. For both species, roots were more vulnerable to cavitation than shoots. Overall, changes in vulnerability from riparian to slope habitats were small for both species. Greater declines in stomatal conductance as the summer proceeded, combined with higher allocation to sapwood and greater sapwood water storage, appeared to contribute to the ability of ponderosa pine to thrive in dry habitats despite relatively high vulnerability to water-stress-induced cavitation.

The shoot-feeding ecology of three Tomicus species in Yunnan Province, southwestern China.

Three Tomicus pine shoot beetles, T. yunnanensis (Kirkendall and Faccoli) (Coleoptera: Scolytidae), T. minor (Hartig), and T. brevipilosus (Wood and Bright), have been causing serious damage to Yunnan pine ( Pinus yunnanensis (Franchet) (Pinales: Pinaceae)) stands in Yunnan, southwestern China. However, their ability to coexist in the crowns of the same trees during the shoot-feeding phase has not been elucidated. In our study, we investigated and compared the shoot-feeding ecology of the three species of pine shoot beetle in P. yunnanensis in Anning County, Yunnan Province. Shoot-feeding by T. yunnanensis, T. minor, and T. brevipilosus initiated in April, May, and June, and ended in February, April, and May, respectively. Individual T. yunnanensis and T. minor adults fed in shoots for about seven months, and T. brevipilosus for nine months, before initiating reproduction. All three Tomicus species fed in the current-year shoots close to the apical bud. No specific overwintering behavior was observed prior to reproduction. The entrance hole of T. yunnanensis was furthest away from the apical bud, and T. minor was the closest to the apical bud. Differences in the spatial distribution of these shoot-feeding sites might reduce competition among the three beetle species. The long-lasting and overlapping shoot-feeding by the three Tomicus species may reduce the resistance of P. yunnanensis and facilitate the reproduction of these beetles in the trunks of living trees, and thus help explain the severe damage by Tomicus in P. yunnanensis.

Tomicus piniperda (Coleoptera: Scolytidae) initial flight and shoot departure along a north-south gradient.

The exotic pine shoot beetle, Tomicus piniperda (L.) (Coleoptera: Scolytidae), established in the north central and northeastern United States (U.S.) and adjacent regions in Canada, is regulated by a federal quarantine that restricts movement of pine material during specific times of the year based on the beetle's life history. Although climatic variation occurs across T. piniperda's range, a single set of dates is used for timing the movement of pine logs. We monitored T. piniperda spring flight, fall shoot departure, and air and internal tree temperatures at three sites along a 300-km north-south gradient in Michigan and Indiana. We also estimated dates for initial spring flight (12 degrees C threshold) and fall shoot departure (0 degrees C threshold) across an 850-km gradient using historical temperature records (1901 to 1999). Average daily temperatures in fall 1997 (8 October to 12 December) and spring 1998 (20 February to 21 April) were 1.8 to 2.4 degrees C colder, respectively, at the northern field site than at the southern field site. Fall shoot departure began at approximately the same time (day 289 to 290) at all three field sites, but complete shoot departure was extended by 3 wk at the southern site (day 336) compared with the northern site (day 317). T. piniperda adults were first captured in funnel traps on calendar day 86 at the northern site and on day 59 at the central and southern field sites. Peak flight occurred at approximately the same time (day 86) at all three sites. Within-shoot temperatures were very similar to air temperatures in the fall and aboveground inside-bark temperatures were similar to air temperatures in the spring. Average predicted dates based on historical temperature records varied by 31 d for initial shoot departure and 84 d for initial spring flight between northern Michigan and southern Indiana. Because considerable variation can occur in T. piniperda behavior across a broad geographic range, dates specified in the U.S. Federal quarantine should be adjusted according to local temperatures.

Phenological patterns of mature longleaf pine ( Pinus palustris Miller) under two different soil moisture regimes

Significant differences in above-ground net primary productivity (ANPP) have been identified along a soil moisture gradient in mature longleaf pine-wiregrass ecosystems [Can. J. For. Res. 29 (1999) 743]. To determine if differences in ANPP were apparent at the individual tree level, patterns of mature longleaf pine ( Pinus palustris Miller) shoot and needle phenology were characterized on xeric and wet/mesic sites in southwest Georgia. Towers provided access to the crowns of the mature trees. Needle abscission patterns were monitored over one growing season (1999); shoot and needle growth patterns were monitored over three growing seasons (1999–2001). Environmental variables, including soil moisture content, predawn needle water potential and gap fraction, as well as several crown structural characteristics, were also measured. Crowns at the two sites had similar average branch characteristics, with the exception of average branch angle, which was significantly greater at the wet/mesic site. The starting dates for shoot elongation and linear shoot growth were similar at the two sites during all 3 years; cessation of shoot growth occurred significantly earlier at the wet/mesic site in 1999. Duration of shoot elongation was longer at the xeric site; however, shoot growth rate was greater at the wet/mesic site. In contrast, during all 3 years, start of needle elongation and start of linear needle growth occurred significantly earlier at the wet/mesic site; cessation of needle growth occurred significantly earlier at the wet/mesic site in 2000. Duration of needle growth was similar at both sites, but needle growth rate was greater at the wet/mesic site in 2000 and 2001. No consistent differences in shoot and needle phenology with crown position were observed, except shoots were longer in the top crown third at the xeric site during 1999 and 2001. Average needle lifespan was determined to be 15 months. Mature longleaf pine exhibited a determinant pattern (one seasonal flush) of shoot and needle growth during the first two growing seasons, and an indeterminate pattern (multiple seasonal flushes) during the third growing season. Soil moisture content was not strongly correlated to patterns of needle abscission; however, predawn needle water potential explained 17% of the variation in early growing season needle demography.

Shoot feeding ecology of Tomicus piniperda and T. minor (Col., Scolytidae) in southern China

Abstract: The pine shoot beetle, Tomicus piniperda, is causing substantial tree mortality to Pinus yunnanensis in south‐western China, whereas the same species in Europe seldom kills Pinus sylvestris. In order to understand this difference in aggressiveness, we studied the shoot feeding ecology of the pine shoot beetles in Yunnan, and compared it with European results. We found many similarities in the shoot feeding behaviour of T. piniperda, and also that of Tomicus minor, which was common locally. In contrast to Europe, however, the pine shoot beetles in Yunnan seem to be able to predispose the host trees for stem attack by intensive shoot‐feeding. It has also been observed that beetles aggregate in certain trees during shoot feeding, but we could not verify that in our experiment.