Host resistance in defoliated pine: effects of single and mass inoculations using bark beetle-associated blue-stain fungi

1 In 1996, 7000 ha of pine forests were defoliated by the pine looper Bupalus piniaria in south‐western Sweden. 2 The susceptibility of trees of different defoliation classes (0, 30, 60, 90 and 100% defoliation) to beetle‐vectored blue‐stain fungi was tested in inoculation experiments. Forty and 120‐year‐old Scots pine trees were inoculated with ‘single’, i.e. a few inoculations of Leptographium wingfieldii and Ophiostoma minus, two blue‐stain fungi associated with the pine shoot beetle Tomicus piniperda. The young trees were also ‘mass’ inoculated with L. wingfieldii at a density of 400 inoculation points per m² over a 60 cm stem belt. 3 Host tree symptoms indicated that only trees with 90–100% defoliation were susceptible to the mass inoculation. 4 Single inoculations did not result in any consistent differences in fungal performance between trees of different defoliation classes, regardless of inoculated species or tree age class. 5 Leptographium wingfieldii produced larger reaction zones than O. minus, and both species produced larger lesions in old than in young trees. 6 As beetle‐induced tree mortality in the study area occurred only in totally defoliated stands, mass inoculations seem to mimic beetle‐attacks fairly well, and thus seem to be a useful tool for assessing host resistance. 7 As even severely defoliated pine trees were quite resistant, host defence reactions in Scots pine seem to be less dependent on carbon allocation than predicted by carbon‐based defence hypotheses.     

Induced defence reaction in Scots pine following stem attacks by Tomicus piniperda

The induced defence reaction of Scots pine Pinus sylvestris to stem attacks by the common pine shoot beetle, Tomicus piniperda (Col, Scolytidae), was studied by inducing natural attacks on young Scots pine trees of different vigour Pruned trees were more heavily attacked by T piniperda than unpruned ones Vigorous trees successfully contained the attacking beetles within resinous lesions, whereas less vigorous trees failed to defend themselves The content of resin acids increased dramatically in the lesions on all trees, and the resin acid composition differed somewhat between some treatments Starch accumulation in the inner bark of the main stem was lower in pruned trees than in unpruned ones, and starch reserves were depleted in the most heavily attacked trees All but one of the unpruned trees survived the attack, whereas most of the severely pruned ones died following attack by beetles at densities exceeding c 300 egg galleries m⁻²     

纵坑切梢小蠹携带云南半帚孢研究

云南半帚孢 (Leptogramphyunnanensis)是纵坑切梢小蠹Tomicuspiniperda重要的共生真菌 ,在纵坑切梢小蠹危害寄主树木过程中发挥着重要作用。研究揭示 ,纵坑切梢小蠹主要通过与受到感染云南半帚孢的韧皮组织的接触携带上云南半帚孢的。纵坑切梢小蠹卵、幼虫和蛹对云南半帚孢的带菌率较高 ,均大于 90 % ,而成虫的带菌率较低。纵坑切梢小蠹的体表和体内均携带有云南半帚孢 ,但体表带菌是纵坑切梢小蠹带菌的主要途径。通过对纵坑切梢小蠹成虫头、足、翅和腹部带菌率的研究发现 ,云南半帚孢在纵坑切梢小蠹各部位的分布大体相同 ,揭示纵坑切梢小蠹没有携带云南半帚孢的特化构造或器官。     

云南切梢小蠹对云南松树的蛀干危害及致死机理

蛀干危害是云南切梢小蠹致死云南松树的关键环节。通过控制云南切梢小蠹蛀干密度,对云南切梢小蠹在自然条件下蛀干行为与危害进行了首次探讨。结果表明,云南切梢小蠹蛀干密度与云南松存活率呈负相关,蛀干密度直接决定云南松死亡或存活。研究发现,蛀干密度115坑/m2是云南松树的最低致死密度阈值,云南松树在蛀干密度低于26.4坑/m2情况下存活,在26.4-115坑/m2有部分存活,超过115坑/m2以后将被害致死。云南切梢小蠹对树干攻击形成有卵和无卵两类坑道。形成无卵坑道的蛀干攻击可导致树势衰弱,形成有卵坑道的蛀干危害严重破坏了韧皮组织,是导致云南松死亡的直接原因。     

云南横坑切梢小蠹生物学研究

横坑切梢小蠹Tomicus minor (Hartig)是云南松Pinus yunnanensis Franchet的主要次期性害虫之一。1980年以来,该虫与纵坑切梢小蠹T. piniperda（L.）一起在中国西南部大量发生,导致数十万公顷云南松林受害。本文报道了横坑切梢小蠹在云南地区的生活史、生长、发育、繁殖等生物学特征。横坑切梢小蠹年生活史为一代,前后两代在冬春季有部分重叠。成虫羽化于4月下旬开始陆续,5 月下旬结束。成虫羽化后即飞到树冠上蛀食枝梢,直到11月发育成熟,开始繁殖。在此期间,每头成虫可以蛀食4～6个枝梢。横坑切梢小蠹在云南没有越冬习性。繁殖期从11月至次年3月。成虫主要在已经受到纵坑切梢小蠹危害的树木的中、下部产卵。繁殖期较纵坑切梢小蠹约迟1周。由于横坑切梢小蠹从枝梢到树干对云南松持续危害,对树木的危害性较在其它地区更为严重。横坑切梢小蠹利用受到纵坑切梢小蠹蛀害的树木繁殖产卵,加强了蠹虫对云南松树的危害,加速了受害树木的死亡进程。横坑切梢小蠹的上述生物生态学特征是该虫对云南松造成严重危害的重要原因。从横坑切梢小蠹虫体和虫坑中检测到伴生真菌云南半帚孢Leptographium yunnanensis。横坑切梢小蠹对该菌的带菌率在蛀梢期为11.5%;在蛀干中期约为10%～26%。     

Gradients and dynamics of inner bark and needle osmotic potentials in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst)

Preconditions of phloem transport in conifers are relatively unknown. We studied the variation of needle and inner bark axial osmotic gradients and xylem water potential in Scots pine and Norway spruce by measuring needle and inner bark osmolality in saplings and mature trees over several periods within a growing season. The needle and inner bark osmolality was strongly related to xylem water potential in all studied trees. Sugar concentrations were measured in Scots pine, and they had similar dynamics to inner bark osmolality. The sucrose quantity remained fairly constant over time and position, whereas the other sugars exhibited a larger change with time and position. A small osmotic gradient existed from branch to stem base under pre‐dawn conditions, and the osmotic gradient between upper stem and stem base was close to zero. The turgor in branches was significantly driven by xylem water potential, and the turgor loss point in branches was relatively close to daily minimum needle water potentials typically reported for Scots pine. Our results imply that xylem water potential considerably impacts the turgor pressure gradient driving phloem transport and that gravitation has a relatively large role in phloem transport in the stems of mature Scots pine trees.     

Oviposition behavior and reproductive success of the cerambycid Acanthocinus aedilis in the presence and absence of the bark beetle Tomicus piniperda

The influence of Tomicus piniperda (L.)(Col.:Scolytidae) attacks on Acanthocinus aedilis (L.)(Col.:Cerambycidae) (1) oviposition behavior, (2) breeding material preference and (3) reproductive success was investigated in caged pine bolts with and without egg galleries of T. piniperda. In addition, A. aedilis oviposition behavior was studied in the field. In the presence of T. piniperda attacks most A. aedilis eggs were laid through the entrance holes of the bark beetle egg galleries. In the absence of bark beetle attacks most A. aedilis eggs were laid at places where the outer bark had been damaged and the phloem was exposed. In cages, A. aedilis preferred to oviposit in bolts with bark beetle attacks. Thus, A. aedilis oviposited in all 17 of bark beetle attacked bolts but in only four of nine bolts without T. piniperda attacks. Neither the number of A. aedilis offspring nor the body size of emerging adults differed significantly between bolts attacked by bark beetles and unattacked bolts. Nor was there any significant relationship between the density of bark beetle egg galleries and the production of A. aedilis offspring.     

Suitability of some southern and western pines as hosts for the pine shoot beetle, Tomicus piniperda (Coleoptera: Scolytidae)

The pine shoot beetle, Tomicus piniperda (L.), is an exotic pest that has become established in North America. Discovered in Ohio in 1992, it has since been found in at least 13 states and parts of Canada. The beetle can cause significant growth loss in pines, and it represents a potential threat to trees in areas where it has not yet become established. To evaluate this threat to native pines, field and laboratory tests were conducted on several common and important southern and western species to determine whether they are acceptable hosts for T. piniperda. Comparisons with Pinus sylvestris L., Scots pine, a preferred natural host for the beetle, were made where possible. Measurements of beetle attack success on southern pine billets showed that Pinus taeda L., Pinus echinata Miller, Pinus elliottii var. elliottii Engelmann, Pinus palustris Miller, and Pinus virginiana Miller (loblolly, shortleaf, slash, longleaf, and Virginia pine, respectively) and two western pines, Pinus ponderosa Lawson and Pinus contorta Douglas (ponderosa and lodgepole pine, respectively), were acceptable for breeding material, but brood production was highly variable. Among the southern pines, P. taeda and P. echinata were susceptible to shoot feeding by T. piniperda, whereas P. elliottii was highly resistant and P. palustris seemed to be virtually immune. Shoot feeding tests on the western pines were conducted only in the laboratory, but there was moderate-to-good survival of adults feeding on both species. It seems that if T. piniperda is introduced into the south and west it will likely establish and may cause some damage to native pines. P. taeda may be affected more than other southern pines because it is the most abundant species, it is readily attacked for brood production, which can result in moderately large broods, and the beetle survives well during maturation feeding on P. taeda shoots.     

Phloem parenchyma cells are involved in local and distant defense responses to fungal inoculation or bark-beetle attack in Norway spruce (Pinaceae)

The anatomical response of Norway spruce bark polyphenolic parenchyma cells (PP cells) to inoculation with the phytopathogenic fungus Ceratocystis polonica and attack by its bark-beetle vector Ips typographus was examined. Fungal inoculation on the periderm surface had no effect, while inoculation just below the periderm or halfway into the phloem (mid-phloem) generated detectable responses within 3 wk. The responses included increase in PP cell size and in periodic acid-Schiff's staining of PP cell phenolics, wound periderm initiation from PP cells, and cambial zone traumatic resin duct formation. Fungi were not seen in samples 3 wk after subperiderm or mid-phloem inoculation, but were found in some samples 6 and 9 wk after mid-phloem inoculation. In contrast, inoculations into the cambium resulted in partial (3 wk) or complete (6 and 9 wk) fungal colonization and death of tissue in the infected area. This indicates that PP cells have defenses capable of inhibiting fungal growth. Samples taken near bark-beetle galleries had similar anatomical responses as inoculated samples, validating the inoculation approach to studying defense responses in spruce. These results show that PP cells represent not only a constitutive defense system, but are also involved in local and remote inducible defenses against fungal and beetle attack.     

Chemical factors affecting the brown-rot decay resistance of Scots pine heartwood

The cell wall chemistry (amount of hemicellulose, f-cellulose, and total lignin) and the concentration of extractives (total acetone-soluble extractives, resin acids, pinosylvins and the total phenolics quantified as tannin acid equivalents) were studied in brown-rot resistant and susceptible juvenile heartwood of Scots pine (Pinus sylvestris L.). The study material consisted of a total of 18 trees from two 34-year-old progeny trials at Korpilahti and Kerimäki. The trees were selected from among 783 trees whose decay rate had previously been screened in a laboratory test using a brown-rot fungus, Coniophora puteana. Samples from neither location showed any significant difference in the concentration (mg/cm³) of hemicellulose, f-cellulose and total lignin between the decay resistant and susceptible trees. At both locations only the concentration of total phenolics was higher in the decay-resistant heartwood than in the decay-susceptible heartwood. At Korpilahti, the amount of acetone-soluble extractives and the concentration of pinosylvin and its derivatives were higher in the resistant than in the susceptible trees.     

纵坑切梢小蠹对云南松蛀害研究

在昆明地区,纵坑切梢小蠹Tomicus piniperda L.表现出枝梢聚集、树干蛀害等重要的行为学特征,形成三种基本蛀害模式。横坑切梢小蠹、蓝色伴生真菌参与了纵坑切梢小蠹危害过程,并在其中发挥积极作用。上述因素的综合影响,加强了纵坑切梢小蠹对云南松Pinus yunnanensis寄主树木的危害能力。     

Laboratory study of conspecific avoidance by host-colonizingDendroctonus frontalis Zimm. (Coleoptera: Scolytidae)

Bark/phloem disk sandwiches (100 cm²) were colonized with one to six mating pairs of the southern pine beetle, Dendroctonus frontalis Zimm., to observe gallery construction and evaluate if avoidance behavior occurs between beetles. Frequencies of turn aways, touches, and crosses (three characteristics used to describe conspecific interaction) all increased significantly with beetle density. A threshold of three mating pairs within the 100- cm² phloem area was the density at which avoidance behavior became evident. At a threshold of five mating pairs the number of gallery crossings was significantly greater than at lower densities. Single and paired female beetles introduced into artificial galleries crossed empty neighboring galleries significantly more often than when neighboring galleries were occupied with other D. frontalis. The data suggest that D. frontalis females can regulate gallery spacing within the host through their ability to detect nearby beetles and their galleries. Possible spacing mechanisms are discussed.     

为害云南松的纵坑切梢小蠹 (Tomicus piniperda)经济阈值的研究(英文)

经过对纵坑切梢小蠹 (TomicuspiniperdaL .)种群密度和云南松 (PinusyunnanensisFranch .)生长状况的长期、仔细的调查 ,加上改进的回归分析方法 ,得出了为害云南松的纵坑切梢小蠹防治上的经济阈值 :当林木枯死率不超过 0 .5 2 %时 ,自然控制因子能控制纵坑切梢小蠹种群不向高密度方向发展 ,因而可以不必防治。当林木枯死率达到 0 .5 0 % ,对应的枯捎率为 0 .6 1 % ,以及对应的平均每株侵入孔数为 0 .6 6时 ,防治费用和挽回损失价值相当。所以 ,若既考虑到经济上的合理性 ,又考虑到控制其种群不向高密度方向发展 ,当林木枯死率超过 0 .5 % ,对应的枯梢率超过 0 .6 1 % ,以及对应的平均每株侵入孔数超过 0 .6 6时 ,就有了进行防治的必要。本文还给出了各云南松林区可以用来根据自己的具体情况计算出适合自己的经济阈值的公式。     

Effect of host tree seasonal phenology on substrate suitability for the pine engraver (Coleoptera: Scolytidae): implications for population dynamics and enemy free space

This study evaluated the effects of seasonal phenology on the substrate quality of susceptible hosts to the pine engraver, Ips pini (Say). We also determined the effects of the duration and method of storage on host quality for purposes of laboratory rearing. Live red pine trees were felled at various times during the season, and I. pini adults from a laboratory colony were established on the logs. Subsamples of logs were stored for various intervals, and then provided to beetles. Subsamples of stored logs were waxed at both ends to prevent water loss before being submitted to the same assays. Suitability of red pine phloem tissue in susceptible hosts declined for I. pini throughout the growing season. As the season progressed, the number of beetle progeny that emerged from colonized hosts dropped substantially. This decline was associated with simultaneous reductions in phloem moisture content. Reduction in host suitability may partially offset any advantage I. pini may gain from colonizing trees after the major predators have become less abundant. Bark beetle brood production decreased significantly with length of storage, regardless of the month of tree felling or the method of storing. Implications for bark beetle population dynamics and laboratory rearing systems are discussed.     

The influence of genetics,defensive chemistry and the fungal microbiome on disease outcome in whitebark pine trees

The invasive fungal pathogen Cronartium ribicola infects and kills whitebark pine (Pinus albicaulis) throughout western North America. Whitebark pine has been proposed for listing under the Endangered Species Act in the USA, and the loss of this species is predicted to have severe impacts on ecosystem composition and function in high‐elevation forests. Numerous fungal endophytes live inside whitebark pine tissues and may influence the severity of C. ribicola infection, either directly by inhibition of pathogen growth or indirectly by the induction of chemical defensive pathways in the tree. Terpenes, a form of chemical defence in pine trees, can also influence disease. In this study, we characterized fungal endophyte communities in whitebark pine seedlings before and after experimental inoculation with C. ribicola, monitored disease progression and compared fungal community composition in susceptible vs. resistant seedlings in a common garden. We analysed the terpene composition of these same seedlings. Seed family identity or maternal genetics influenced both terpenes and endophyte communities. Terpene and endophyte composition correlated with disease severity, and terpene concentrations differed in resistant vs. susceptible seedlings. These results suggest that the resistance to C. ribicola observed in natural whitebark pine populations is caused by the combined effects of genetics, endophytes and terpenes within needle tissue, in which initial interactions between microbes and hosts take place. Tree genotype, terpene and microbiome combinations associated with healthy trees could help to predict or reduce disease severity and improve outcomes of future tree breeding programmes.     

THE STUDY OF THE ECONOMIC THRESHOLD OF TOMICUS PINIPERDA (COLEOPTERA: SCOLYTIDEA) ON YUNNAN PINE

Abstract By careful and long period field investigation of the population density of Tomicus piniperda L. and the growth of Yunnan pine ( Pinus yunnanensis French.), and improved regression analysis, the economic threshold of Tomicus piniperda on Yunnan pine is determined: When the death rate of the trees is not more than 0.52%, the natural control factors can prevent the density of the bark beetle from increasing and no control measure is needed. When the death rate of the trees reaches 0.5%, the corresponding rate of shoots attacked is 0.61% and the mean of invading holes per tree 0.66, the cost for control is equal to the economic loss saved. So, considering both the economic justification and the prevention of the pest density from increasing, when the death rate of the trees is more than 0.5%, the corresponding rate of shoots attacked more than 0.61% and the mean of invading holes per tree more than 0.66, control measure should be taken. The paper also gives formulae for different Yunnan pine forest areas to calculate their own economic threshold according to their special situations.     

Occurrence of Bursaphelenchus mucronatus (Nematoda: Aphelenchoididae) and the microhabitat distribution of fungi in declining pine trees in a locale in Korea

A total of 33 pine trees with symptoms of decline were collected in Jeonnam Province, South Korea, and were examined for the presence of nematodes. About 20% of the trees sampled were positive with Bursaphelenchus species. All Bursaphelenchus species were found in recently dead or dying trees. Based on morphological observations, the nematode extracted from the declining pine trees was identified as B. mucronatus. The highly pathogenic pine wood nematode B. xylophilus was not found in any pine trees sampled. B. mucronatus was easily reared on fungus Botrytis cinerea. Twenty one fungal isolates were isolated from dead trees, fallen twigs, and healthy pine trees. The fungal isolates belonged to Trichoderma genus and were dominant in the wood of partially declining pines. The blue‐stain fungi transmitted by the Monochamus beetle were not detected. The B. mucronatus population decreased markedly on Auxarthron reticulatum DY‐2 isolated from soils. The number of nematodes also reduced on Verticillium saksenae A‐1, a nematophagous fungus, and Beauveria bassiana, an entomopathogenic fungus. This observation suggested the fungal production of nematicidal activity against B. mucronatus. When the fungal culture filtrates were also used for nematicidal activity on B. mucronatus, the culture filtrates of A‐1, DY‐2 and B. bassiana showed over 50% mortality within 48 h exposure. The fungi BC4, BC5 and BC6 isolated from declining pine trees inhibited the reproduction of B. mucronatus, and their culture filtrates also expressed nematicidal activity, indicating a possible interaction between the fungi in pine trees and nematodes at microhabitat level.     

Death of vigorous trees benefits bark beetles

Bark beetles (Coleoptera: Scolytidae) are commonly associated with live host trees that are stressed, a relationship that has been attributed to lower host defenses or greater nutritional quality of these trees. However, most bark beetle species commonly inhabit freshly dead trees where induced host defenses are absent. In this study, we investigate the role of tree vigor at the time of death for pine engraver bark beetles, Ips pini (Say), breeding in freshly dead jack pine, Pinus banksiana Lamb. As indices of tree vigor, we considered tree size, phloem thickness, and several measures of recent growth rate (last year's growth increment, mean annual increment and basal area increment in the past 5 and 10 years, and periodic growth ratio). We examined the relationship between these indices in three stands, aged 60, 77, and 126 years, and found that phloem thickness, previously shown to have a strong positive effect on bark beetle reproduction, was only weakly associated with tree growth rate and inconsistently related to tree size among the three stands. To examine the effects of tree vigor on pine engraver reproduction, we felled 20 trees of various sizes from the 77-year-old stand, and experimentally established breeding males and females in 25-cm-long sections. Offspring were collected and characteristics of breeding galleries were measured. Using stepwise regression, we consistently found that indices associated with tree growth rate best explained beetle reproductive performance, as they were positively related to parental male and female establishment on logs, female reproductive success, length of egg galleries, proportion of eggs resulting in emerged offspring, and negatively related to the length of the post-egg gallery. Surprisingly, phloem thickness had no unique effect on pine engraver reproduction, except for a weak negative effect on the establishment success of parental females. The strong effect of tree vigor observed in this study suggests that substantial mortality of vigorous trees, such as caused by windthrow, can contribute to significant increases in bark beetle populations that could trigger outbreaks in living trees. Received: 3 February 1999 / Accepted: 27 April 1999