Sudden death of cocoa in Papua New Guinea associated with Phytophthora palmivora cankers invaded by bark beetles

An extensive survey in 1976-82 indicated that sudden death of cocoa was widespread in Papua New Guinea with losses up to 1% per month in trees over 10-yr-old, especially in neglected plantations. Over 95% trees affected had large Phytophthora palmivora canker lesions and over 90% of the cankers were invaded by bark beetles. In an intensive single year survey of one plot 18-8% of 69 healthy trees died. Ambrosiella spp., P. palmivora and Fusarium solani were isolated from wood surrounding beetle tunnels but only the last two caused extensive lesions when inoculated into the xylem of healthy trees. The evidence obtained indicated that the sudden death syndrome is initiated by P. palmivora cankers on trunks and main branches but bark beetles are a major contributory factor and fungi associated with their tunnels may contribute to the problem. There is a risk of further outbreaks of the disease as cocoa cultivars susceptible to P. palmivora continue to be planted.     

Cork oak vulnerability to fire: the role of bark harvesting, tree characteristics and abiotic factors

Forest ecosystems where periodical tree bark harvesting is a major economic activity may be particularly vulnerable to disturbances such as fire, since debarking usually reduces tree vigour and protection against external agents. In this paper we asked how cork oak Quercus suber trees respond after wildfires and, in particular, how bark harvesting affects post-fire tree survival and resprouting. We gathered data from 22 wildfires (4585 trees) that occurred in three southern European countries (Portugal, Spain and France), covering a wide range of conditions characteristic of Q. suber ecosystems. Post-fire tree responses (tree mortality, stem mortality and crown resprouting) were examined in relation to management and ecological factors using generalized linear mixed-effects models. Results showed that bark thickness and bark harvesting are major factors affecting resistance of Q. suber to fire. Fire vulnerability was higher for trees with thin bark (young or recently debarked individuals) and decreased with increasing bark thickness until cork was 3-4 cm thick. This bark thickness corresponds to the moment when exploited trees are debarked again, meaning that exploited trees are vulnerable to fire during a longer period. Exploited trees were also more likely to be top-killed than unexploited trees, even for the same bark thickness. Additionally, vulnerability to fire increased with burn severity and with tree diameter, and was higher in trees burned in early summer or located in drier south-facing aspects. We provided tree response models useful to help estimating the impact of fire and to support management decisions. The results suggested that an appropriate management of surface fuels and changes in the bark harvesting regime (e.g. debarking coexisting trees in different years or increasing the harvesting cycle) would decrease vulnerability to fire and contribute to the conservation of cork oak ecosystems.     

Spatial and temporal dynamics of bark beetles in Chinese white pine in Qinling Mountains of Shaanxi Province, China

Spatial and temporal dynamics of bark beetles in single tree trunks of Pinus armandi were studied in Qinling Mountains, Shaanxi Province, China. Ten species of engraver bark beetles attacked from healthy to withered Chinese white pines, but seven species were commonly detected every year in Qinling forest ecosystem. Dendroctonus armandi and Hylurgops longipilis were common species at the lower of trunks, and Ips acuminatus, Polygraphus sinensis, and Pityogenes japonicus primary distributed in the middle of trunks, whereas population densities of Cryphalus lipingensis and C. chinlingensis centralized at the upper trunks and branches of Chinese white pines. On the time series, D. armandi, as a dominant species in Chinese white pines of Qinling forest ecosystem, mainly attacked healthy and weakened trees and cooperated with blue stain fungus that resulted in the declining abruptly resistance and triggered the secondary bark beetles to attack the infected or withered host trees. Attacking and colonizing phenology of bark beetles in Qinling forest ecosystem are caused by complex interactions among spatial and trophic competition and cooperation and exhibit particular spatial and temporal patterns. Our results support the view that competition and cooperation within bark beetles are a critical factor to influence bark beetles spatial and temporal distribution, and stability of bark beetles' ecosystem, D. armandi, I. acuminatus, P. japonicus, P. sinensis, C. lipingensis, C. chinlingensis, and H. longipilis in Chinese white pine of Qinling forest ecosystem.     

Brenneria alni,causal agent bark canker of Alnus subcordata

In 2014, bark cankers were observed on Caucasian alder (Alnus subcordata) trees in Iran. The disease was characterized by a dark watery liquid often exuding from longitudinal cankers in the bark of the tree trunks which stained the surface. Symptomatic tissue from A. subcordata was sampled from a number of sites in the Mazandaran province. Isolations were performed on nutrient agar supplemented with sucrose (SNA) and yielded bacterial colonies that were uniform, round and whitish. The bacterial strains isolated from alder trees in Iran were similar to Brenneria alni based on phenotypic and genotypic (nucleotide sequences of the 16S rRNA, and housekeeping genes gyrB, and infB) characteristics. The pathogenicity of the representative strains was determined by inoculating stem pieces of A. subcordata. All tested strains caused longitudinal necrotic lesions 30 days after inoculation and were re-isolated from this tissue. To our knowledge, this is the first report of the occurrence of B. alni in Iran, and on A. subcordata globally.     

Pinewood Nematode,Bursaphelenchus xylophilus,Associated with Red Pine, Pinus resinosa,in Western Maryland

Red pines Pinus resinosa in Garrett and Allegany counties, Maryland, were examined during 1982-84 to determine distribution of the pinewood nematode, Bursaphelenchus xylophilus, within and among trees. Approximately 25-year-old (younger) and 47-year-old (older) trees were subdivided into the following categories: 1) trees with mostly green needles; 2) trees with mostly reddish-brown needles; 3) trees lacking needles but with bark intact; 4) trees lacking both needles and bark; and 5) trees with chlorotic, bleached-green needles. Bursaphelenchus xylophilus was found infecting 68% of younger red pines and 77% of older red pines. Nematodes were not evenly distributed in trees within any given tree decadence category or in trees of the same age. Nematodes were recovered from 20% of wood samples from trunks and primary and secondary branches in younger pines and from 15 % of older red pines. On the basis of tree decadence category, the highest incidence of infection in younger trees (31%) was in bleached-green needled trees (category 5), whereas in older trees the highest infection (25%) occurred in green needled trees (category 1). At both sites trunks were infected more often than branches.     

The Late Triassic Araucarioxylon Arizonicum trees of the Petrified Forest National Park, Arizona, USA

Examination and measurement of many of the trunks attributed to Araucarioxylon arizonicum Knowlton eroded from the Late Triassic Chinle Formation in the Petrified Forest National Park, Arizona demonstrate that the living tree did not closely resemble any of the present-day Araucaria trees of the southern hemisphere as postulated in past reconstructions. The research indicates that it was a tall monopodial tree with branches occurring in a disordered manner on the trunk from the base to the crown. Calculations using the allometric method of Niklas indicate that the trees were of considerable size. The largest recorded trunk has a basal diameter of nearly 3 m and may represent a tree 59 m high, when living. The root system of the A. arizonicum tree consisted of a ring of four to six steeply inclined lateral roots and a massive, vertically directed tap root. Many of the trunks still have their root systems attached, a circumstance that indicates their felling by the cut-bank operations of the local river system. The massive roots of these trunks, particularly the large tap root, are consistent with growth in soft, deep, alluvial soil, and the thin scale bark is to be expected in a tropical climate free from frost.     

The detection of plum pox virus in Prunus species by enzyme-linked immunosorbent assay (ELISA)

Plum pox virus (PPV) was detected by ELISA throughout the year in extracts of root, bark, fruit, flowers and leaves of Prunus species; extracts from healthy plants gave negligible background reactions. In the summer, ELISA values obtained with extracts from infected leaves were variable but samples extracted at 1:50 (w/v) could have been diluted a further five to 110 times before reaching the limit of detection. Using a single antiserum the virus was detected in several hundred trees, suggesting that there was little antigenic variation. PPV was unevenly distributed in leaves and shoots and commonly occurred in only a few branches of an infected tree although it was frequently present in suckers growing from the roots. Virus was detected in the only three trees known to be infected in random leaf samples taken from 530 1-yr-old trees, but some infected trees were missed in samples taken from older trees and from a 7-yr-old rootstock hedge. The main practical use of ELISA for PPV is therefore as a sensitive and highly reliable confirmatory test which greatly facilitates control of the disease by the prompt destruction of infected trees.     

SEXUAL DIMORPHISM AND DIVERGENCE IN WINTER FORAGING BEHAVIOUR OF THREE-TOED WOODPECKERS PICOIDES TRIDACTYLUS

Measurements of 48 males and 45 females of Three-toed Woodpeckers shot in Norway revealed that the mean lengths of wing, tail, bill and tarsus of males were significantly greater than those of females. Sexual dimorphism was most marked for the bill and tarsus.
Feeding observations of the species from spruce-dominated mixed forests during the October-March period indicated an intersexual partitioning of the foraging niche. The males exhibited a stereotyped foraging pattern of bark scaling low down on the main trunks of dead spruce, whilst females used a more differentiated feeding technique and utilized a greater variety of trunk and branch sizes of dead, decaying and living trees of several different species. Significant intersexual differences were found in tree height preference and in the diameter of trunks and branches. The males foraged almost exclusively on the trunks of trees over 10 m high and over 15 cm in diameter, whilst females often frequented dead spruce, under 5 m high, and foraged on thinner trunks and branches. Foraging height was significantly lower for males than for females.
The relationship between the sexual dimorphism, the intersexual partitioning of the feeding niche and their biological significance, is briefly discussed.     

The lichen flora on Picea abies in a suboceanic spruce forest area in Central Norway with emphasis on the relationship to site and stand parameters

The lichen flora on 400 Picea abies trees (branches, trunks and trunk bases) in 100 patches of suboceanic spruce forest in Central Norway has been investigated. Relationships between occurrence of the species and a number of habitat and tree variables were analysed by detrended correspondence analysis (DCA). A total of 122 lichen species were recorded. Total species number was found to be about the same on branches and trunk bases (considerably lower on trunks), but with higher β-diversity on trunk bases. Most species could be classified as branch specialists, generalists, trunk or trunk base specialists. Among the measured habitat variables, stand age, altitude and vegetation type were found to be the most important for explaining the patterns of species distributions. Alectoria sarmentosa, Mycoblastus sanguinarius and several dry bark species on trunks, including Caliciales species, were more or less confined to old forests, while Usnea spp. were more abundant in young form. Trentepohlia-containing trunk base species like Arthonia vinosa, Dimerella pineti, Lecanactis abietina and Sclerophora coniophaea showed preference for vegetation types indicating nutrient-rich substrates. The number of branch species was highest on lower altitudes while the opposite was true for trunk species. Larger trees with rough bark in older stands had a more species-rich lichen flora, probably because of higher substratum area and availability of more diverse microsites.     

萧氏松茎象的生活史、产卵和取食习性

萧氏松茎象Hylobitelus xiaoi是严重蛀害国外松的新害虫。在江西赣南地区两年发生一代,以幼虫在蛀道、成虫在蛹室或土中越冬。卵和蛹的发育起点温度分别为8.4℃和7.5℃,有效积温分别为215.9和345.3日·度。各虫态历期：13～28℃间,卵为52.9～11.4天;13～30℃间,蛹为60.1～16.4天; 25℃恒温下,幼虫128.9天。成虫靠爬行活动,极少飞翔。成虫具夜出性活动节律：即傍晚上树行取食、交配和扩散等活动,早晨回到树干基部或土缝中。成虫需取食松枝作为补充营养,产卵前期46.3天,产卵期 105.3天,卵产于近表土的寄主树皮内,每雌产卵35.7粒。幼虫5～7龄,以幼树危害最烈。     

Thermal properties and fauna on the bark of trees in two different African ecosystems

Summary The thermal properties of 26 African tree species in two different ecosystems were studied using thermocouples. In a subtropical moist forest were three bark types of trees: species with thin and smooth bark types with low values of insulation across the bark; species with a more structured bark type and medium insulation values; and species with deep-fissured or scaly bark types and high insulation values. Only these latter trees are able to survive openings in the subtropical forest and stand alone on edges of forest gaps. In the savanna all tree species showed adaptations in the structure of their bark in different forms: many tree species shade their trunks. Some have low bark insulation and these are known to be sensitive to fires. Some tree species show high bark insulation and do not shade their trunks. Tree species with white bark avoid overheating of their surface by reflection of the radiation. The arthropod community living exclusively on the bark was investigated for the first time on South African trees, on ten tree species. In the two different ecosystems this habitat is occupied by different arthropod groups. In the subtropical forest Acari, Araneae, Opiliones, Isopoda, Myriopoda, Blattodea, Psocoptera, Heteroptera, Coleoptera, Formicidae, and Nematocera (Diptera) are the main arthropod groups living exclusively on the bark of trees. In the savanna Pseudoscorpiones, Araneae, Collembola, Blattodea, Psocoptera, Coleoptera, Neuroptera, Termites, Formicidae, Hymenoptera and Brachycera (Diptera) are the main arthropod groups living exclusively on the bark of trees. Within one ecosystem on one bark type the dominant species are similar; richly structured bark types have a richer fauna. In the forest, bark arthropod diversity is related to the bark structure of the constituent trees, and the arthropod communities on the bark would reflect changes in the structure of the forest. Forests comprising tree species with different bark types would have a richer total bark arthropod fauna. Specialists on richly structured bark types would die out if tree species composition were altered by man to give stands consisting only of tree species with smooth bark types. Bark arthropods in a subtropical moist forest have different proportions of herbivorous and fungivorous compared to carnivorous species than those on the bark of trees in a savanna.     

天然赤松个体生物量的研究

对延边地区不同密度天然赤松林中不同生长势的赤松个体地上部生物量进行了研究。结果表明,不同生长势赤松生物量变化受密度影响的顺序为：优势木〈平均木〈被压木;各器官生物量分配比例受密度影响的顺序为：干〉枝〉叶〉皮。不同生长势赤松的生物量垂直分布虽然各具特点,但都表现为：树干和树皮生物量主要分布在６ｍ树高范围内,树枝则集中在６～１０ｍ范围,针叶在上、中、下３层林冠中均分,上层林冠的枝叶量受密度影响最小。     

Host specificity of ambrosia and bark beetles (Col., Curculionidae: Scolytinae and Platypodinae) in a New Guinea rainforest

Abstract.  1. Bark and ambrosia beetles are crucial for woody biomass decomposition in tropical forests worldwide. Despite that, quantitative data on their host specificity are scarce.
2. Bark and ambrosia beetles (Scolytinae and Platypodinae) were reared from 13 species of tropical trees representing 11 families from all major lineages of dicotyledonous plants. Standardised samples of beetle-infested twigs, branches, trunks, and roots were taken from three individuals of each tree species growing in a lowland tropical rainforest in Papua New Guinea.
3. A total of 81 742 beetles from 74 species were reared, 67 of them identified. Local species richness of bark and ambrosia beetles was estimated at 80–92 species.
4. Ambrosia beetles were broad generalists as 95% of species did not show any preference for a particular host species or clade. Similarity of ambrosia beetle communities from different tree species was not correlated with phylogenetic distances between tree species. Similarity of ambrosia beetle communities from individual conspecific trees was not higher than that from heterospecific trees and different parts of the trees hosted similar ambrosia beetle communities, as only a few species preferred particular tree parts.
5. In contrast, phloeophagous bark beetles showed strict specificity to host plant genus or family. However, this guild was poor in species (12 species) and restricted to only three plant families (Moraceae, Myristicaceae, Sapindaceae).
6. Local diversity of both bark and ambrosia beetles is not driven by the local diversity of trees in tropical forests, since ambrosia beetles display no host specificity and bark beetles are species poor and restricted to a few plant families.     

Fusarium solani association with branch and trunk cankers on citrus weakened by cold weather in Florida

Injury or inoculation of apparently healthy citrus trunk bark and wood with Fusarium solani immediately prior to and after the December 1983 freeze resulted in cankers similar to natural branch and trunk cankers which formed on trees following the freeze. Fusarium solani was consistently isolated from active lesions of natural and induced cankered bark. Phytophora spp. were not isolated from cankered tissue. Earliest cankers appeared as a water-soaked area under the bark around the point of inoculation, later F. solani sporodochia formed on the bark surface. Older cankers became dry and cracked but produced no gum. Canker size ranged from 10–90 cm vertical diameter in spring 1984 inoculations but were only several cm diameter following late summer inoculations. Active cankers developed again after inoculation following the January 1985 freeze. Similar cankers were produced on Hamlin sweet orange stems inoculated with F. solani.     

Are tree trunks habitats or highways? A comparison of oribatid mite assemblages from hoop-pine bark and litter

Abstract Oribatid mites (Acari: Oribatida) are among the most diverse and abundant inhabitants of forest soil and litter, but also have species-rich assemblages on bark and in the canopies of trees. It is unclear whether the trunk of a tree acts simply as a 'highway' for movement of mites into and out of the canopy, or whether the trunk has a distinctive acarofauna. We compare oribatid assemblages from the trunk bark of hoop pine ( Araucaria cunninghamii ) with those from litter collected beneath the same trees. A 1.0 by 0.5 m area of bark was sampled from three trees at each of five sites using a knockdown insecticide. A 1-L sample of leaf litter was collected as close as possible to the base of each sampled tree. Mites were extracted using Tullgren funnels, identified to genus and morphospecies, and counted. Assemblages were almost 100% distinct, with only one oribatid morphospecies ( Pseudotocepheus sp.) collected from both litter and bark. Litter had a higher taxon richness than bark in total and per sample, but oribatids made up a greater percentage of the acarofauna in the bark samples. We had expected that the more consistent physical substrate of bark would be reflected in greater similarity of oribatid faunas on trunks than in litter; however, the opposite proved to be the case. We conclude that hoop-pine trunks are habitats rather than highways for oribatid mites. Based on the observed higher turnover among bark faunas, tree trunks may represent habitat islands whose colonisation by particular oribatid species is more stochastic than that of the more continuous 'sea' of litter.     

Can Norway spruce trees be ‘vaccinated’ against attack by Ips typographus?

1 A field experiment was carried out to test the hypothesis that treatment of Norway spruce trees with the Ips typographus-transmitted blue-stain fungus Ceratocystis polonica enhances tree resistance to later mass attack by this bark beetle. 2 Twenty-five mature trees were pretreated by inoculating a non-lethal dose of the fungus into the bark, while 18 trees served as untreated controls. Three and a half weeks after treatment a bark beetle attack was initiated by attaching dispensers with I. typographus pheromone to the tree trunks. 3 A significantly larger proportion (67%) of the control trees than of the pretreated trees (36%) were killed by the beetle attack. The result is discussed in relation to recent results regarding defence mechanisms in Norway spruce trees.     

Eastern filbert blight disease resistance from <Emphasis Type="Italic">Corylus americana</Emphasis> ‘Rush’ and selection ‘Yoder #5’ maps to linkage group 7

Eastern filbert blight (EFB), caused by the pyrenomycete Anisogramma anomala, is a serious threat to the hazelnut industry in the Pacific Northwest. EFB is endemic in eastern North America where it occasionally produces small cankers on the wild American hazelnut (Corylus americana). In contrast, most cultivars of European hazelnut (Corylus avellana) are susceptible. Genetic resistance is the most promising disease control method and is an objective of the Oregon State University hazelnut breeding program. ‘Gasaway’ resistance, which is governed by a dominant allele at a single locus, has been extensively used in the program. However, ‘Gasaway’ and some of its offspring have been infected by EFB isolates from New Jersey, Minnesota, and Michigan. Efforts to create new cultivars with durable EFB resistance include identifying and studying new resistance sources. In this study, resistant accessions C. americana ‘Rush’ and interspecific hybrid selection ‘Yoder #5’ were crossed with susceptible C. avellana selections and the resulting segregating seedling populations were inoculated by either exposure of potted trees under a structure topped with diseased branches or field exposure supplemented by tying diseased branches to each tree. Disease response was scored when cankers were visible 20 months after inoculation. Resistance from both sources segregated in a 1:1 ratio, indicating control by a single locus and a dominant allele for resistance. DNA extracted from the seedlings was amplified with previously mapped microsatellite markers. Resistance from both C. americana ‘Rush’ and ‘Yoder #5’ was placed on linkage group 7 in the same position as resistance from C. avellana ‘Ratoli.’ Linked microsatellite markers B753, GB372, and B509 will be useful for marker-assisted selection and the pyramiding of genes for durable EFB resistance. Assessing response to EFB is challenging, whether the plants are inoculated under a structure topped with diseased wood or in a humidity chamber in the greenhouse, or by exposure in the field. The pathogen has a 2-year life cycle, and there is a 15-month wait between inoculation and symptom expression. A small number of escapes is commonly encountered, and resistant plants occasionally develop small cankers. Our approach of studying segregation ratios and then mapping with microsatellite markers should be a useful approach for disease resistance studies in many tree crops.     

Exploring Regional Variation in Roost Selection by Bats: Evidence from a Meta-Analysis

Background and Aims

Tree diameter, tree height and canopy closure have been described by previous meta-analyses as being important characteristics in roost selection by cavity-roosting bats. However, size and direction of effects for these characteristics varied greatly among studies, also referred to as heterogeneity. Potential sources of heterogeneity have not been investigated in previous meta-analyses, which are explored by correlating additional covariates (moderator variables). We tested whether effect sizes from 34 studies were consistent enough to reject the null hypothesis that trees selected by bats did not significantly differ in their characteristics from randomly selected trees. We also examined whether heterogeneity in tree diameter effect sizes was correlated to moderator variables such as sex, bat species, habitat type, elevation and mean summer temperature.

Methods

We used Hedges’ g standardized mean difference as the effect size for the most common characteristics that were encountered in the literature. We estimated heterogeneity indices, potential publication bias, and spatial autocorrelation of our meta-data. We relied upon meta-regression and multi-model inference approaches to evaluate the effects of moderator variables on heterogeneity in tree diameter effect sizes.

Results

Tree diameter, tree height, snag density, elevation, and canopy closure were significant characteristics of roost selection by cavity-roosting bats. Size and direction of effects varied greatly among studies with respect to distance to water, tree density, slope, and bark remaining on trunks. Inclusion of mean summer temperature and sex in meta-regressions further explained heterogeneity in tree diameter effect sizes.

Conclusions

Regional differences in roost selection for tree diameter were related to mean summer temperature. Large diameter trees play a central role in roost selection by bats, especially in colder regions, where they are likely to provide a warm and stable microclimate for reproductive females. Records of summer temperature fluctuations inside and outside tree cavities that are used by bats should be included in future research.     

Linking increasing drought stress to Scots pine mortality and bark beetle infestations

In the dry Swiss Rhone Valley, Scots pine forests have experienced increased mortality in recent years. It has commonly been assumed that drought events and bark beetles fostered the decline, however, whether bark beetle outbreaks increased in recent years and whether they can be linked to drought stress or increasing temperature has never been studied. In our study, we correlated time series of drought indices from long-term climate stations, 11-year mortality trends from a long-term research plot, and mortality probabilities modeled from tree rings (as an indicator of tree vitality) with documented occurrences of various bark beetle species and a buprestid beetle, using regional Forest Service reports from 1902 to 2003 and advisory cases of the Swiss Forest Protection Service (SFPS) from 1984 to 2005. We compared the historical findings with measured beetle emergence from a 4-year tree felling and breeding chamber experiment. The documented beetle-related pine mortality cases increased dramatically in the 1990s, both in the forest reports and the advisory cases. The incidents of beetle-related pine mortality correlated positively with spring and summer temperature, and with the tree-ring based mortality index, but not with the drought index. The number of advisory cases, on the other hand, correlated slightly with summer drought index and temperature, but very highly with tree-ring-based mortality index. The tree-ring-based mortality index and observed tree mortality increased in years following drought. This was confirmed by the beetle emergences from felled trees. Following dry summers, more than twice as many trees were colonized by beetles than following wet summers. We conclude that increased temperatures in the Swiss Rhone Valley have likely weakened Scots pines and favored phloeophagous beetle population growth. Beetles contributed to the increased pine mortality following summer drought. Among the factors not addressed in this study, changed forest use may have also contributed to increased beetle populations and Scots pine mortality, whereas air pollution seems to be of lesser importance.     

Attraction of ambrosia and bark beetles to coast live oaks infected by Phytophthora ramorum

1 Sudden oak death is caused by the apparently introduced oomycete, Phytophthora ramorum. We investigated the role of bark and ambrosia beetles in disease progression in coast live oaks Quercus agrifolia. 2 In two Marin County, California sites, 80 trees were inoculated in July 2002 with P. ramorum and 40 were wounded without inoculation. Half of the trees in each group were sprayed with the insecticide permethrin [cyclopropanecarboxylic acid, 3‐(2,2‐dichloroethenyl)‐2,2‐dimethyl‐(3‐phenoxyphenyl) methyl ester] to prevent ambrosia and bark beetle attacks, and then were sprayed twice per year thereafter. After each treatment, sticky traps were placed on only the permethrin‐treated trees. Beetles were collected periodically in 2003. 3 Inoculated trees accounted for 95% of all beetles trapped. The ambrosia beetles Monarthrum scutellare and Xyleborinus saxeseni and the western oak bark beetle Pseudopityophthorus pubipennis were the most abundant of the seven species trapped. 4 Permethrin treatment delayed initiation of beetle attacks and significantly reduced the mean number of attacks per tree. Beetles did not attack any wounded or noncankered inoculated trees. 5 Trees with larger cankers trapped more beetles early in the disease. Once permethrin lost effectiveness, the number of beetle entrance tunnels was a more reliable predictor of subsequent trap catch than was canker size. 6 Beetles were initially attracted to P. ramorum cankers in response to kairomones generated in the host‐pathogen interaction. After beetles attacked the permethrin‐treated trees, aggregation pheromones most probably were the principal factor in beetle colonization behaviour.