Beetle Attack Research Articles

Potato virus Y infection hinders potato defence response and renders plants more vulnerable to Colorado potato beetle attack.

In the field, plants are challenged by more than one biotic stressor at the same time. In this study, the molecular interactions between potato (Solanum tuberosum L.), Colorado potato beetle (Leptinotarsa decemlineata Say; CPB) and Potato virus YNTN (PVYNTN) were investigated through analyses of gene expression in the potato leaves and the gut of the CPB larvae, and of the release of potato volatile compounds. CPB larval growth was enhanced when reared on secondary PVYNTN-infected plants, which was linked to decreased accumulation of transcripts associated with the antinutritional properties of potato. In PVYNTN-infected plants, ethylene signalling pathway induction and induction of auxin response transcription factors were attenuated, while no differences were observed in jasmonic acid (JA) signalling pathway. Similarly to rearing on virus-infected plants, CPB larvae gained more weight when reared on plants silenced in JA receptor gene (coi1). Although herbivore-induced defence mechanism is regulated predominantly by JA, response in coi1-silenced plants only partially corresponded to the one observed in PVYNTN-infected plants, confirming the role of other plant hormones in modulating this response. The release of β-barbatene and benzyl alcohol was different in healthy and PVYNTN-infected plants before CPB larvae infestation, implicating the importance of PVYNTN infection in plant communication with its environment. This was reflected in gene expression profiles of neighbouring plants showing different degree of defence response. This study thus contributes to our understanding of plant responses in agro-ecosystems.

A mixed severity disturbance regime in the primary Picea abies (L.) Karst. forests of the Ukrainian Carpathians

Natural disturbance regimes play key roles in shaping forest structure and development at stand and landscape levels. Disturbances are commonly complex and variable, such that classical dichotomous characterization of disturbance regimes as following large infrequent disturbances or patch dynamics is too simplistic, especially when the resulting damage is more severe than the baseline of a single tree patch dynamic, but not severe enough to represent large infrequent disturbance. Ongoing climate change affects mountain Picea abies forests in Central, East and Southeastern Europe by an increasing frequency of storms and bark beetle outbreaks. We present a unique study based on extensive dataset aimed to reveal the spatiotemporal pattern of the disturbance history and role of the mixed severity disturbances in primary spruce mountain forest landscapes in the Ukrainian Carpathians.We reconstructed canopy disturbance history and maximum disturbance severity using ca. 2396 tree cores in 96 sample plots. Neither large-scale stand-replacement nor fine scale dynamics was the prevailing disturbance over the last four centuries. Rather, we observed a complex spatiotemporal pattern of mixed severity disturbances. Canopy turnover time ranged between 50 and 300years and depended on the maximum severity of the disturbance event. Spatial analyses revealed no similarity in spatiotemporal pattern across disturbance histories or maximum disturbance severities. We observed evidence of a combination of variable severity disturbances that fails to fit the classical scheme of gap or patch dynamics with sharply defined sizes and borders, but is more consistent with a mixed severity disturbance regime across the landscape. Windstorms were likely the most important past disturbance agent. The probability of an epidemic bark beetle attack was low, although the possibility of small local outbreaks cannot be excluded. An additional, potentially overlooked, agent of disturbance could be historic periods of extreme cold.This reconstructed disturbance regime may challenge existing silvicultural systems in the Carpathians, calling for a more complex spatiotemporal forest management approach. However, mimicking a mixed severity disturbance regime can be done at the forest management level by applying a range of disturbance severities at the stand level.

Forest disturbance effects on snow and water yield in interior British Columbia

Long-term studies at Mayson Lake (ML) and Upper Penticton Creek (UPC) in British Columbia's southern interior quantify snow-dominated hydrologic response to natural disturbances and logging. Following natural disturbance at ML, changes in snow accumulation related directly to mountain pine beetle attack were measurable by the fifth year following attack, when canopy transmittance had increased 24% due to needlefall. In year 1, April 1 snow water equivalent (SWE) was 48% higher in the clearcut than in the pine forest. This difference was reduced to 23% by year 8. A 3-year lag in snow response was also observed in a nearby burned stand where SWE was on average 27 and 59% higher in the clearcut than in the burn and forest, respectively. At UPC, April 1 SWE averaged 12% more and 12% less in a low and high elevation clearcut than forest, respectively, and snow disappeared ∼10 days earlier in both clearcuts. Partially as a result of snowmelt synchronization from higher with lower elevations after 50% of the treatment watersheds had been clearcut, April water yield increased and June to July yield decreased. Research results improve evaluation of hydrologic response to forest disturbance, including retention of beetle-killed stands versus salvage logging.

First Report of Laurel Wilt Caused by Raffaelea lauricola on Bay Laurel (Laurus nobilis) in the United States

Bay laurel (Laurus nobilis L.) is an economically important evergreen tree of the family Lauraceae. It is native to Asia Minor and the Balkans and was introduced into the United States for its ornamental and culinary uses (4). In September 2013, a 6-m-tall bay laurel in Gainesville, FL, attracted our attention because it had wilted leaves, discolored sapwood, and ambrosia beetle entrance holes, all symptoms of laurel wilt. In addition, the tree was growing close to an avocado that succumbed to the disease months earlier. In an effort to determine whether the laurel wilt pathogen (Raffaelea lauricola T.C. Harr., Fraedrich & Agaveya) was, indeed, involved in the decline of the tree of current interest, discolored sapwood was sectioned into 5-mm2 pieces, surface disinfested for 30 s in a 4% sodium hypochlorite solution, and plated onto CSMA media (1,2). Within 7 to 14 days, cream-colored, adpressed fungal growth typical of R. lauricola grew from the sapwood pieces (2). DNA was extracted from an isolate of a single conidium (PL1634) and a portion of the 18S rRNA gene was PCR-amplified with primers NS1/NS4, resulting in a 1,021-bp amplicon (GenBank Accession No. KF913344.1), with a BLASTn search revealing 100% homology to several R. lauricola isolates (3). To confirm pathogenicity, six bay laurel seedlings (0.5 m) and a silk bay (0.65 m) (Persea humilis, susceptible control) were wounded twice with a 0.5-mm-diameter drill bit. Then, 30 μl of a spore suspension of PL1634 (1.38 × 105 condia/plant) were introduced into the xylem by pipette and the wounds were wrapped in Parafilm (1). Negative controls consisted of a mock-inoculated (water) and non-inoculated bay laurel plus a mock-inoculated silk bay. Plants were placed in a growth chamber set to a 16/8 h (25/22°C) diurnal light/temperature cycle. After 60 days, all fungal-inoculated plants were completely wilted with dead leaves and subsequent necrosis of stems, while mock- and non-inoculated controls remained asymptomatic. Sapwood dissection revealed xylem discoloration similar to the original infected tree, and fungi morphologically similar to PL1634 were recovered from all inoculated plants upon isolation on CSMA media. Mock- and non-inoculated controls lacked vascular discoloration and fungal growth on media. In order to determine if the redbay ambrosia beetle, Xyleborus glabratus Eichoff (laurel wilt vector) could successfully reproduce in this host, symptomatic branches (7 cm in diameter) of L. nobilis with external evidence of ambrosia beetle attack (frass "toothpicks") were placed in a plastic rearing box within a growth chamber (25°C). Within 4 weeks of incubation, dozens of immature and mature X. glabratus beetles emerged. This is the first record of Koch's postulates being completed for R. lauricola on L. nobilis and the ability of X. glabratus to infest and breed in its stems. This information may be of importance in the event of an introduction of X. glabratus and its fungal associate to Mediterranean areas where bay laurel is either growing wild or being cultivated as valuable commercial crop.

Xyleborus glabratus attacks and systemic colonization by Raffaelea lauricola associated with dieback of Cinnamomum camphora in the southeastern United States

SummaryLaurel wilt, caused by Raffaelea lauricola, is responsible for extensive mortality of redbay and other American members of the Lauraceae in the southeastern United States. Raffaelea lauricola is a mycangial symbiont of the redbay ambrosia beetle (Xyleborus glabratus), and the beetle and fungus were accidentally introduced from Asia. Branch dieback of camphortree (Cinnamomum camphora), an Asian member of the Lauraceae, has been occasionally observed in areas where laurel wilt has decimated redbay populations, and R. lauricola was isolated from such camphortrees. However, the role of X. glabratus and R. lauricola in this branch dieback remains unclear. Examination of camphortrees on Jekyll Island, Georgia showed that healthy‐appearing trees and those with branch dieback had been attacked by X. glabratus, but the trees with branch dieback had four times as many beetle attacks. Raffaelea lauricola was routinely isolated from discoloured xylem near beetle tunnels in healthy trees and those with dieback. Single‐point inoculations with R. lauricola on stems of mature, healthy camphortree trees failed to induce wilt‐like symptoms or branch dieback, although areas of discoloration were scattered throughout the xylem, and R. lauricola was reisolated irregularly at various heights in some inoculated trees. In growth chamber experiments, single‐point inoculations with R. lauricola resulted in systemic colonization but no wilt symptoms or branch dieback in camphortree saplings. In contrast, inoculations at multiple points along the stem (simulating multiple attacks by the vector) caused branch dieback and wilt‐like symptoms, including a brownish, diffuse discoloration of the xylem. Camphortree appears to be more resistant than American species of Lauraceae to the vascular wilt caused by R. lauricola. The fungus does colonize camphortrees systemically, however, and can apparently cause branch dieback. This suggests that the fungus may provide brood material for X. glabratus in Asia as it does in the southeastern United States.

Interactions among the Mountain Pine Beetle, Fires, and Fuels

Bark beetle outbreaks and wildfires are principal drivers of change in western North American forests, and both have increased in severity and extent in recent years. These two agents of disturbance interact in complex ways to shape forest structure and composition. For example, mountain pine beetle, Dendroctonus ponderosae Hopkins, epidemics alter forest fuels with consequences for the frequency and intensity of wildfires and, conversely, fire injury to trees can promote bark beetle attack and increase beetle populations. Given the great influence these processes have on forest ecosystems, a better understanding of how bark beetles and fires interact is needed to better manage forests and to predict and manage wildfires. Here we review current knowledge on how fire and bark beetles interact, focusing on the mountain pine beetle. We highlight research on how fuel reduction treatments and wildfires affect bark beetles and how bark beetles can affect wildfires by modifying the moisture content, chemistry, and structure of fuels. Last, we discuss the implications these findings have for fire management and firefighter safety.

Ethanol accumulation during severe drought may signal tree vulnerability to detection and attack by bark beetles

Tree mortality from temperature-driven drought is occurring in forests around the world, often in conjunction with bark beetle outbreaks when carbon allocation to tree defense declines. Physiological metrics for detecting stressed trees with enhanced vulnerability prior to bark beetle attacks remain elusive. Ethanol, water, monoterpene concentrations, and composition were examined in the phloem and sapwood of drought-stressed Aleppo pine (Pinus halepensis Mill.) freshly attacked by mature Mediterranean pine shoot beetles (Tomicus destruens (Wollaston, 1865)) and in neighboring unattacked trees. The attacked trees were more water-stressed and contained, on average, 2.1 and 2.4 times more ethanol in the phloem and sapwood, respectively, than the neighboring attack-free trees. This response is consistent with the known attraction of T. destruens to ethanol. Most monoterpene concentrations in the phloem, but not sapwood, were greater in tissues of attacked trees, whereas compositional differences were minor between the two tree groups for both tissues. Tissue water content explained much of the variation in phloem monoterpene concentrations, which increased as water in the phloem declined, suggesting that higher constitutive quantities existed in the more stressed trees prior to the attacks. Monoterpenes may have contributed to host tree selection by T. destruens, but their potential influence is considered less important than that of ethanol based on beetle responses to these compounds in previous trapping studies. This is the first report of elevated ethanol concentrations in tissues of trees experiencing natural drought stress and suggests that ethanol measurements in severely water-stressed trees may allow early detection of those most vulnerable to bark beetle attack.

On correcting the time-lag bias in aerial-surveyed bark beetle infestation data

Bark beetles are among the main biotic hazards affecting forests worldwide. Aerial surveys are an appropriate and commonly used tool for detecting and monitoring bark beetle infestations at the landscape scale. However, a considerable time-lag in the aerial-surveyed data limits its use, e.g. for analyses which include temporary factors.This temporal lag is caused by the gradual decay of the host tree following a bark beetle attack. A change in the spectral signature in aerial imagery indicates an attack with a delay of several weeks or even months. Thus, aerial-surveyed infestation data suffer a temporal shift, i.e. infestations detected for a specific time period cannot be directly assumed to have been initiated within that same period. The present study introduces an algorithm which assigns the most probable time of Ips typographus L. attack to infestations detected by aerial surveys. To calculate the infestations initiated within a certain year x the algorithm considers the potential attack period, the assumed time-lag, as well as the date of aerial surveys and the amount of detected infestation from the years x, x−1 and x+1. The deviation between infestations detected by aerial survey and those actually initiated (as calculated by the algorithm) quantifies the correction effect, i.e. the time-lag bias. The algorithm was then applied to a data set which covers a time series of 26 consecutive years, including both managed and non-managed infestations. To account for uncertainty in the input variables or to mimic varying environments the application considers three different scenarios. Over all three scenarios results indicate substantial deviations, which may be either positive or negative. Further, deviation is shown to be affected by the length of the time-lag and the attack period, as well as by variations in survey dates and infestation frequency of consecutive years. Finally, the time-corrected infestation data provides a threefold benefit: (i) The temporal pattern of oscillating population dynamics is truly reflected. (ii) Comprehensive correlation analyses which include dynamic environmental covariates, e.g. temperature, precipitation, or antagonists, are facilitated. (iii) Aerial-surveyed and ground-surveyed monitoring data can be easily related whether within a region or between regions. In conclusion, this study increases the value of aerial-surveyed infestation data for bark beetle monitoring and research.

Effect of natal and colonised host species on female host acceptance and male joining behaviour of the mountain pine beetle (Coleoptera: Curculionidae) using pine and spruce

AbstractThe mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), outbreak in British Columbia and Alberta, Canada, currently extends over 18.3 million ha of pine forest. The principal host of the insect is lodgepole pine, Pinus contorta var. latifolia Englemann (Pineaceae) although it is a generalist herbivore on pines. Mountain pine beetles do not typically colonise spruce. However, during the current outbreak, several instances of mountain pine beetle attack on interior hybrid spruce, Picea glauca (Moench) Voss×Picea engelmannii Parry ex. Engelmann (Pinaceae) have been noted in areas where severe lodgepole pine mortality has occurred. Occasionally, beetle reproduction within spruce has been successful. Reproductive behaviours of mountain pine beetles reared from pine and spruce, such as female host acceptance and male joining behaviour, were studied on bolts of pine and spruce in laboratory bioassays. Females more readily accepted spruce host material relative to pine. Females that developed in spruce had higher rates of host acceptance of both pine and spruce host material than females that had developed in pine. We interpret these latter results with caution, however, as inference is partially restricted by sourcing viable insects from one spruce in this study. Implications of these findings to the concepts of host adaptation and population dynamics of this eruptive herbivore are discussed.

Impact of Intercropping Sorghum and Okra on the Incidence of Flea Beetles of Okra <i>Podagrica</i> spp in Dalwa, Maiduguri Semi-Arid Zone of Nigeria

Field experiments were conducted at faculty of Agriculture teaching and research farm, university of Maiduguri in 2010 and 2011 rainy seasons. The aim was to investigate the impact of intercropping sorghum with okra on the incidence of flea beetle of okra (Podagrica spp) in the semi-Arid zone of Nigeria. The results showed that sole crop okra suffered flea beetle attack which affected its growth, fruit formation, fruit weights and fruit yield. Intercropping okra with sorghum significantly reduced the flea beetle populations, leaf damage caused by Podagrica spp (Coleoptera: Chrysomelidae). While increasing number of leaves for photosynthetic activities, plant height, fruit formation, fresh fruit weight and total fruit yield. The study concluded that okra intercropping at 1:1, 1:2 and 2:2 are the most efficient and productive intercrop systems in flea beetle management. Okra intercropping with cereal sorghum was found to be good for sustainable agriculture and organic farming in Nigeria due to its numerous advantages, particularly with respect to insect pests’ control.

A Host Creates an Enemy‐free Space for Mistletoes by Reducing Seed Predation Caused by a Woodboring Beetle: A Hypothesis

AbstractParasitic plants rely on host plants for nutrition. The number of host species varies largely between groups, from single species or genus to hundreds of species. Relative abundance of the host and evolutionary history are the main requisites for parasitic plants to develop specificity to abundant hosts. In the present study, we suggest a novel mechanism by which a hemiparasitic mistletoe can develop local specificity mediated by its host. First, we describe a novel interaction in which a woodboring beetle (Hypothenemus obscurus) preys on mistletoe seeds (Psittacanthus plagiophyllus) attached to tree branches. This beetle preys more frequently on seeds deposited on branches of non‐host species than on branches of its unique local host species (53 percent on average vs. 26 percent respectively). We hypothesize that local host specificity for this mistletoe could be partly mediated by beetle‐host incompatibility, since the host offers a predation‐free space in which mistletoes have better chances to grow. Furthermore, that the exceptional gum exudates produced by this unique host species minimize beetle attacks on branches, thus reducing predation of mistletoe seeds. This novel tritrophic interaction opens an avenue for research on macroscopic host‐specificity mechanisms that occur at the level of the host bark and that have been poorly studied by plant ecologists.

Fuel treatments and landform modify landscape patterns of burn severity in an extreme fire event.

Under a rapidly warming climate, a critical management issue in semiarid forests of western North America is how to increase forest resilience to wildfire. We evaluated relationships between fuel reduction treatments and burn severity in the 2006 Tripod Complex fires, which burned over 70,000 ha of mixed-conifer forests in the North Cascades range of Washington State and involved 387 past harvest and fuel treatment units. A secondary objective was to investigate other drivers of burn severity including landform, weather, vegetation characteristics, and a recent mountain pine beetle outbreak. We used sequential autoregression (SAR) to evaluate drivers of burn severity, represented by the relative differenced Normalized Burn Ratio index, in two study areas that are centered on early progressions of the wildfire complex. Significant predictor variables include treatment type, landform (elevation), fire weather (minimum relative humidity and maximum temperature), and vegetation characteristics, including canopy closure, cover type, and mountain pine beetle attack. Recent mountain pine beetle damage was a statistically significant predictor variable with red and mixed classes of beetle attack associated with higher burn severity. Treatment age and size were only weakly correlated with burn severity and may be partly explained by the lack of treatments older than 30 years and the low rates of fuel succession in these semiarid forests. Even during extreme weather, fuel conditions and landform strongly influenced patterns of burn severity. Fuel treatments that included recent prescribed burning of surface fuels were particularly effective at mitigating burn severity. Although surface and canopy fuel treatments are unlikely to substantially reduce the area burned in regional fire years, recent research, including this study, suggests that they can be an effective management strategy for increasing forest landscape resilience to wildfires.

Impact of Intercropping Sorghum and Okra on the Incidence of Flea Beetles of Okra <i>Podagrica</i> spp in Dalwa, Maiduguri Semi-Arid Zone of Nigeria

Field experiments were conducted at faculty of Agriculture teaching and research farm, university of Maiduguri in 2010 and 2011 rainy seasons. The aim was to investigate the impact of intercropping sorghum with okra on the incidence of flea beetle of okra (Podagrica spp) in the semi-Arid zone of Nigeria. The results showed that sole crop okra suffered flea beetle attack which affected its growth, fruit formation, fruit weights and fruit yield. Intercropping okra with sorghum significantly reduced the flea beetle populations, leaf damage caused by Podagrica spp (Coleoptera: Chrysomelidae). While increasing number of leaves for photosynthetic activities, plant height, fruit formation, fresh fruit weight and total fruit yield. The study concluded that okra intercropping at 1:1, 1:2 and 2:2 are the most efficient and productive intercrop systems in flea beetle management. Okra intercropping with cereal sorghum was found to be good for sustainable agriculture and organic farming in Nigeria due to its numerous advantages, particularly with respect to insect pests’ control.

Flavan-3-ols in Norway spruce: biosynthesis, accumulation, and function in response to attack by the bark beetle-associated fungus Ceratocystis polonica.

Proanthocyanidins (PAs) are common polyphenolic polymers of plants found in foliage, fruit, bark, roots, rhizomes, and seed coats that consist of flavan-3-ol units such as 2,3-trans-(+)-catechin and 2,3-cis-(-)-epicatechin. Although the biosynthesis of flavan-3-ols has been studied in angiosperms, little is known about their biosynthesis and ecological roles in gymnosperms. In this study, the genes encoding leucoanthocyanidin reductase, a branch point enzyme involved in the biosynthesis of 2,3-trans-(+)-flavan-3-ols, were identified and functionally characterized in Norway spruce (Picea abies), the most widespread and economically important conifer in Europe. In addition, the accumulation of flavan-3-ols and PAs was investigated in Norway spruce saplings after wounding or inoculation with the fungal pathogen Ceratocystis polonica, which is vectored by bark beetles (Ips typographus) and is usually present during fatal beetle attacks. Monomeric and dimeric flavan-3-ols were analyzed by reverse-phase high-pressure liquid chromatography, while the size and subunit composition of larger PAs were characterized using a novel acid hydrolysis method and normal phase chromatography. Only flavan-3-ol monomers with 2,3-trans stereochemistry were detected in spruce bark; dimeric and larger PAs contained flavan-3-ols with both 2,3-trans and 2,3-cis stereochemistry. Levels of monomers as well as PAs with a higher degree of polymerization increased dramatically in spruce bark after infection by C. polonica. In accordance with their role in the biosynthesis of 2,3-trans-(+)-flavan-3-ols, transcript abundance of Norway spruce LEUCOANTHOCYANIDIN REDUCTASE genes also increased significantly during fungal infection. Bioassays with C. polonica revealed that the levels of 2,3-trans-(+)-catechin and PAs that are produced in the tree in response to fungal infection inhibit C. polonica growth and can therefore be considered chemical defense compounds.

Crown fire potential in lodgepole pine forests during the red stage of mountain pine beetle attack

Mountain pine beetle (MPB) outbreaks within the previous 10–15 years have affected millions of hectares of lodgepole pine forests in western North America. Concerns about the influence of recent tree mortality on changes in fire behaviour amongst firefighters and fire managers have led researchers to attempt to quantify the effects on crown fire potential. In this paper we provide an up-to-date reviewand critiqueof research that has endeavoured toquantify the effect of recent MPB-caused tree mortality, during the red stage, on crown fire potential based upon quantitative descriptions of important crown and canopy fuel characteristics and simulation-based assessments of crown fire initiation and spread using operational and physics-based models. While significant progress has been made in characterizing the important variables affecting crown fire potential in recentlyattacked forests, we suggest that many of the conclusions drawn from simulation-based studies conducted to-date are suspect given the use of inappropriate and/or un-validated models. A systematic program of experimental burning, the monitoring and documentation of wildfires and prescribed fires, and better models of fuel moisture and fuel structure are urgently needed in order to properly assess crown fire potential in lodgepole pine forests recently attacked by the MPB.

Smooth bark surfaces can defend trees against insect attack: resurrecting a ‘slippery’ hypothesis

SummarySmooth bark on trees and shrubs was historically hypothesized to be an anatomical defence against epiphytic vegetation and phytophagous insects. This hypothesis has fallen from favour, yet no clear tests of bark texture as a defence against insects have been published.We tested the smooth bark defence hypothesis using bark beetles specialized in attacking pine trees as model insects, andPinus flexilis(limber pine) – a widespread tree that can have both smooth and rough bark surfaces on the same stem – as the model tree. We investigated the effects of bark texture on the locations of bark beetle attacks on trees with a combination of field surveys and experiments in the Colorado Rocky Mountains, USA.Bark beetle attacks were overwhelmingly located on rough bark surfaces and virtually absent from smooth bark. Increasing proportional coverage by smooth bark was negatively related to bark beetle attacks per square metre of bark surface. Experimental tests of bark beetles' ability to grip smooth versus rough bark revealed that bark beetles have difficulty gripping and quickly fell from smooth bark but not from rough bark.Smooth bark was negatively related to increasing tree size, but our models indicated that even partial coverage by smooth bark on a tree's trunk can significantly reduce total bark beetle attacks – this reduction likely improves tree fitness as bark beetles must aggregate to overcome tree defences.Synthesis. Our results indicate that smooth bark on trees can act as an anatomical defence against insects by reducing their ability to grip a tree's surface – even for insects specialized in attacking tree stems. Similar to other forms of anti‐insect defence (i.e. secondary chemistry, leaf toughness), smooth bark appears to be influenced by plant ontogeny whereby younger trees have greater defences than older trees. Understanding the adaptive significance of bark texture will require continued field and genetic study. Nevertheless, our results revealed that smooth bark texture increases tree resistance to phytophagous insects calling for the resurrection and vetting of the smooth bark defence hypothesis.

Composition and Elevation of Spruce Forests Affect Susceptibility to Bark Beetle Attacks: Implications for Forest Management

The spruce bark beetle, Ips typographus (L.) (Coleoptera: Curculionidae, Scolytinae), is one of the most destructive insects infesting spruce forests in Europe. Data concerning infestations of I. typographus occurring over the last 19 years (1994–2012) on the Southern Alps were analyzed in seven spruce forest types: (1) pure spruce plantations; (2) pure spruce reforestations; (3) pure spruce mountain forests; (4) pure spruce alpine forests; (5) spruce-conifer mixed forests; (6) spruce-broadleaf mixed forests; and (7) spruce-conifer-broadleaf mixed forests. The collected data included the amount of I. typographus damage and the location and composition of the infested forests. The results indicate that different forest types are differently susceptible to I. typographus. Plantations, reforestations and mountain spruce forests show mean damage and mean number of infestations higher than other forest types. Within pure spruce forests, alpine forests growing at high elevations (>1300 m) suffer low damage. Furthermore, the mean number of infestation spots recorded annually in the different spruce forest types is negatively correlated with a Naturality Index value. The results suggest that forest composition and elevation are the main factors driving the risk of I. typographus damage. A new management strategy for some spruce forest types is needed, with a progressive reduction of pure spruce forests at low altitude and an increase of broadleaf composition.

New geographical distribution and seasonality of Costalimaita ferruginea (Coleoptera: Chrysomelidae) on Eucalyptus urograndis in Guiricema, Minas Gerais, Brazil

Costalimaita ferruginea (Fabricius) (Coleoptera: Chrysomelidae) is a voracious defoliator, responsible for big losses associated to eucalyptus plantations. The attack of this pest can be characterized by the appearance of holes in the leaves and consequent fall, which reduces the photosynthetic potential, and thus slows the development of plants attacked. The objective of this research was to report the new occurrence and characterize the period of attack of beetle C. ferruginea in plantations of hybrid Eucalyptus grandis x Eucalyptus urophylla (= Eucalyptus urograndis) (Myrtaceae) in municipality of Guiricema, Minas Gerais State, Brazil. The period of monitoring started in December 2006 and extended until December 2012. The first attacks of C. ferruginea in this region started in the end of September, and showed a peak of population and greater intensity of damage from mid-October until the second week of November.

Association between resistance to an introduced invasive pathogen and phenolic compounds that may serve as biomarkers in native oaks

California coast live oaks (Quercus agrifolia Nee) have suffered large losses from sudden oak death, caused by the introduced oomycete Phytophthora ramorum. Infected mature coast live oaks exhibit cankers on the main stem that produce a viscous sap-derived exudate, referred to as bleeding. Subsequent attacks by ambrosia and bark beetles, followed by the activity of fungi introduced by these insects, have led to mortality levels greater than 50% since the mid-1990s. Despite an infection rate of 5% year−1, asymptomatic trees still persist in many heavily infected stands after more than 15years of exposure to the pathogen. We hypothesized that varying responses to P. ramorum, including apparent recovery from infections, reflected phenotypic differences in susceptibility. In this study we evaluated the relationship between the early development of symptoms in mature trees that were experimentally inoculated with P. ramorum and long-term survival. A logit model showed that external canker lengths measured 9months following inoculation predicted survival 7years later. We defined resistance to P. ramorum in the surviving trees as absence or cessation of bleeding after the 7years of the study and absence of beetle attacks on bleeding trees. Probability of resistance was also predicted by external canker length measured 9months after inoculation. Canker length distribution was consistent with quantitative resistance to P. ramorum. The role of plant chemistry in resistance was examined by quantifying soluble phenolics in phloem methanol extracts prepared from the surviving trees. A logistic regression model found that expression of resistance was associated with four phenolic compounds; ellagic acid and a partially characterized ellagic acid derivative, and two chromatographic peaks that represent two uncharacterized phenolic compounds. Ellagic acid and a crude methanol extract from coast live oak phloem (total phenolics) were fungistatic when assayed in vitro at physiologically relevant levels and total phenolics were fungicidal at the highest concentration tested. The association of certain phenolics with resistance may facilitate the use of biomarkers in minimally invasive assays to predict the response of trees to P. ramorum, thereby increasing the options for managing threatened forests.

The effect of stem density on the probability of attack by the ambrosia beetlePlatypus quercivorusvaries with spatial scale

The ambrosia beetle Platypus quercivorus uses fagaceous tree species as its hosts, and causes Japanese oak wilt by transporting and introducing the pathogenic fungus Raffaelea quercivora into the host tree. To protect fagaceous trees, it is necessary to understand the host selection process used by the beetle in heterogeneous forests. The occurrence of beetle attack on Quercus crispula and Castanea crenata was monitored from 2008 to 2011 in two 1-ha and one 0.5-ha plots established in a secondary forest. The stem and crown densities of each fagaceous tree species were calculated at 11 different spatial scales for each individual tree. Model application and selection were performed to clarify factors affecting the probability of attack by P. quercivorus. As shown in previous studies, a higher probability of attack was predicted for Q. crispula than for C. crenata, and the predicted probability of attack was lower for trees attacked in the previous year. The effect of stem density on the probability of attack was positive at a small (radius 5 m) spatial scale and negative at larger (radius 5–17.5 m) scales. We interpreted this to indicate that a dense distribution of fagaceous trees in a small area had a higher probability of attack, and that this probability decreased with an increasing density of fagaceous trees in a surrounding concentric area. A positive effect of crown density was detected, suggesting that P. quercivorus has a means of detecting host trees in areas with high crown densities of fagaceous species.