Attack Density Research Articles

Corrosion Behavior of Alloyed Cast Iron in Ethylene Glycol-Based Engine Coolants at Elevated Temperature

For enhanced engine performance, corrosivity of the engine coolants would play a significant role. In this work, corrosion investigation was performed on cast iron material in pre-mixed engine coolant environment to understand the threshold limits of contaminants. The pre-mixed coolant contained combination of organic additives viz. sebacate (SA), 2-ethylhexanoate (2-EH), and tolyltriazole (TTA) with varying concentrations of chloride contaminant. Constant immersion of cast iron samples in engine coolant with different chloride levels at 90 °C was followed by room temperature electrochemical tests. The potentiodynamic polarization tests showed no instability until 100 ppm chloride additions exposed up to 28 days. At lower frequencies in electrochemical impedance spectroscopy (EIS) spectra, inhibition layer characteristics changed from highly capacitive to highly resistive and concurrently a sharp decrease in charge transfer resistance was observed with time for samples exposed to >100 ppm chloride levels. In the longer duration corrosion tests, higher pit depths with increased number density of attacks were observed for cast iron samples exposed to engine coolants containing >100 ppm chloride. For elevated temperature exposures a threshold limit of <200 ppm chloride was established for cast iron samples.

Thick bark can protect trees from a severe ambrosia beetle attack.

Thick bark has been shown to protect trees from wildfires, but can it protect trees from an ambrosia beetle attack? We addressed this question by examining the distribution of holes of the invasive Kuroshio Shot Hole Borer (KSHB, Euwallacea kuroshio; Coleoptera: Scolytinae) in the bark of Goodding’s black willow (Salix gooddingii), one of the KSHB’s most-preferred hosts. The study was conducted in the Tijuana River Valley, California, in 2016–17, during the peak of the KSHB infestation there. Using detailed measurements of bark samples cut from 27 infested trees, we tested and found support for two related hypotheses: (1) bark thickness influences KSHB attack densities and attack locations, i.e., the KSHB bores abundantly through thin bark and avoids boring through thick bark; and (2) bark thickness influences KSHB impacts, i.e., the KSHB causes more damage to thinner-barked trees than to thicker-barked trees. Our results indicate that thick bark protects trees because it limits the density of KSHB entry points and thereby limits internal structural damage to low, survivable levels. This is the first study to identify bark thickness as a factor that influences the density of KSHB—or any ambrosia beetle—in its host tree, and the first to link bark thickness to rates of host tree mortality.

Distribution pattern of entry holes of the tree-killing bark beetle Polygraphus proximus.

Bark beetles attack their hosts at uniform intervals to avoid intraspecific competition in the phloem. Bark texture and phloem thickness also affect bark beetle attacks, and the bark characteristics are not spatially homogeneous; therefore, the distribution patterns of entry holes can demonstrate an aggregated distribution. Polygraphus proximus Blandford (Coleoptera: Scolytinae) is a non-aggressive phloephagous bark beetle that feeds on Far Eastern firs. They have caused mass mortality in Russia and Japan. However, the distribution pattern of entry holes of P. proximus and spatial relationships with bark characteristics have not been studied. Thus, we investigated the distribution pattern of entry holes of P. proximus. The distribution of entry holes was significantly uniform in most cases. As the attack density increased, an aggregated distribution pattern within a short distance (< 4.0 cm) was observed. The rough bark had a significantly higher number of entry holes than the remaining bark. The distribution pattern of entry holes demonstrated a significantly aggregated spatial association with rough bark. Finally, rough bark around knots had significantly thicker phloem than the remaining barks. These suggest that P. proximus may preferentially attack rough bark to reproduce in the thicker phloem under a rough bark surface.

Terrorism vulnerability assessment in Java Island: a spatial multi-criteria analysis approach

Terrorism is one of the Indonesia’s national security threat. The attack mostly happens in Java Island, attracted by the dense population, also because the island is a center for economic and governance. The spatial pattern of terrorism attack shows correlations with the spatial density of the targeted attack. Therefore, this study assesses the spatial vulnerability of Java Island using a spatial multi-criteria analysis (SMCA). The main attributes analyzed were the density of the past terrorist attack, arrested area, police/military facility, government facility, business center, densely populated area, and church, determine that in the case of a terrorist attack is strongly affected by the attraction of the area.

A flexible approach for predicting and mapping postfire wood borer attacks in black spruce and jack pine forests using the differenced normalized burn ratio (dNBR)

Postfire salvage logging is used to reduce economic losses; however, burned trees are rapidly colonized by wood-boring insects, which reduce the merchantable value of the wood. This study aims to predict wood borer (Monochamus Megerle in Dejean, 1821) attacks after wildfire as a function of rapidly available variables such as tree basal area, stem diameter, and burn severity using the differenced normalized burn ratio (dNBR). In 2011, we sampled 60 black spruce (Picea mariana (Mill.) Britton, Sterns &amp; Poggenb.) or jack pine (Pinus banksiana Lamb.) plots in five burns from 2010 in the Haute-Mauricie region of Quebec, Canada. A 50 cm bole section was debarked on seven trees in each plot to estimate wood borer attack density. Wood borer attacks were more abundant in black spruce than in jack pine. As a continuous variable, dNBR unveiled a quadratic effect of burn severity on attack density in black spruce, which was higher at moderate burn severity. In jack pine, the highest levels of attack density were found at high burn severity. Models produced in this article will help forest managers to better prioritize areas for salvage logging and thus reduce economic losses due to wood borer activity.

Susceptibility of Eurasian Scots pine, Pinus sylvestris L., to the aggressive North American mountain pine beetle, Dendroctonus ponderosae Hopkins

Introductions of alien forest insects can exert substantial ecological and economic impacts on natural forest systems. The mountain pine beetle, Dendroctonus ponderosae Hopkins, an aggressive bark beetle native to western North America, kills mature pines at outbreak levels and is currently expanding its geographic, altitudinal and host ranges across the continent. Its oligophagous feeding behavior and its ability to kill novel hosts in newly invaded areas of Alberta, Canada suggest that this insect could threaten pine forests in other regions of the world. Little is known of the susceptibility of Scots pine, Pinus sylvestris L., to mountain pine beetle. Scots pine is a potential novel host common to forests across Eurasia and introduced to North America. Laboratory studies indicate the insects can colonize and reproduce in harvested logs of the host. We measured outcomes of an outbreak by mountain pine beetle in mixed stands of mature Scots pine and ponderosa pine, P. ponderosa Dougl. ex. Laws. var. scopulorum Engelm., a historical host for the insect, in the Black Hills of South Dakota, U.S.A. We conducted a retrospective assessment of beetle attack and tree mortality of 165 trees (54 Scots pine and 111 ponderosa pine) of similar size and proximity that experienced high beetle pressure for three to four years ending in 2015. Our results show that mountain pine beetle can detect and attack live trees of Scots pine. Notably, we found that nearly 90% of Scots pines showed signs of attack, while no evidence of attack was found on the historical host in mixed stands. However, we found that Scots pines received half the attack density and demonstrated fifteen fold less likelihood of mortality in one year’s time relative to ponderosa pine in nearby stands. These results are important for assessing the potential for mountain pine beetle to kill trees in Eurasia and North America in Scots pine stands.

Site- and tree-related factors affecting colonization of cork oaks Quercus suber L. by ambrosia beetles in Tunisia

Ambrosia beetles are emerging globally as important agents of tree death and decline. In this work, we observed highly variable attack intensity by ambrosia beetles in cork oak stands in Tunisia. A correlation between the proportion of infested trees and average temperature was found. Tree diameter and tree phytosanitary variables further contribute to the attack densities of ambrosia beetles. Results can be relevant for preventive measures aiming to conserve this natural forest heritage. Cork oak woodlands comprise a unique Mediterranean ecosystem supporting rich biological diversity and providing multiple services. A decline of cork oak forests has been observed in several regions of the Mediterranean Basin in the last four decades, which can be related to climate change, novel biotic agents, and changes in management practices. The ambrosia beetles have been one of the major biotic agents associated with cork oak decline, mostly in the western Mediterranean. Assess the presence and attack densities of ambrosia beetles in cork oak Tunisian forests. A total of 15 sites located in North Western of Tunisia, comprising 729 sample trees were evaluated. Using generalized linear models, the presence and density of ambrosia beetles’ holes were related to tree and site variables. Variables related to climate, tree (dendrometric parameters, debarking intensity) and biotic agents were examined. The proportion of trees attacked per site varied from 0 to 100%; in four sites, it exceeded 50%. At the site level, the average temperature and tree diameter were the main variables explaining the proportion of attacked trees. Sites with warmer climates showed higher incidence of ambrosia beetles. At the tree level, the presence of attacks increased with tree diameter and concomitantly with intensity of debarking, as well as the presence of tree trunk cavities. The presence and density of insect attacks were related to tree diameter, area of debarking, and phytosanitary conditions. However, 19% of the trees attacked by ambrosia beetles had no signs of other biotic agents or decline. At the site level, attack rates increased with temperature and tree diameter. A warmer climate may change insect behavior from that of a non-aggressive pest to that of an aggressive bark beetle. Adaptive forest management practices are needed to reduce infestations.

Effect of Sirex noctilio (Hymenoptera: Siricidae) attack density on Pinus sylvestris (Pinaceae) survival

AbstractPopulation density is often a critical factor in colonisation of trees by bark and wood-boring insects and may determine whether an exotic species is likely to establish and spread. In a manipulative field study, we investigated whether density of the attacking population of an exotic invasive woodwasp, Sirex noctilio Fabricius (Hymenoptera: Siricidae), affected survival and time-to-death of a favoured host tree, Pinus sylvestris Linnaeus (Pinaceae). We introduced mating pairs of woodwasps to stressed P. sylvestris at either high (15 mating pairs, nine trees) or low (two mating pairs, nine trees) density. More trees died, and more quickly, when exposed to the high versus low density of S. noctilio (78% versus 33% of trees). In the high-density treatment, year of tree death was synonymous with production of a S. noctilio F1 cohort (one-year or two-year generation time); this pattern was not as consistent in the low-density treatment. Although sample size was limited, our results indicate that attack density affects S. noctilio colonisation of P. sylvestris.

Biological Aspects of Mountain Pine Beetle in Lodgepole Pine Stands of Different Densities in Colorado, USA

Research Highlights: The biology of mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins, in Colorado’s lodgepole pine forests exhibits similarities and differences to other parts of its range. Brood emergence was not influenced by stand density nor related to tree diameter. The probability of individual tree attack is influenced by stocking and tree size. Findings have implications for understanding MPB as a disturbance agent and for developing management strategies. Background and Objectives: MPB causes extensive tree mortality of lodgepole pine, Pinus contorta Douglas ex Loudon, across the western US and Canada and is probably the most studied bark beetle in North America. However, most of the current knowledge on the biology and ecology of MPB in lodgepole pine comes from the Intermountain Region of the US and western Canada. Little information is available from Colorado. This is the first study addressing effects of stand stocking levels on the biology of MPB and quantifying phloem consumption. In addition, although data are available on the conditions that foster stand infestation, this is the first study estimating the probability of individual tree attack among stands of known different stocking. Materials and Methods: Studies were conducted in managed lodgepole pine stands in Colorado. Unbaited traps were used to monitor MPB flight across stands of different densities. Cages were used to monitor emergence and bark samples to determine attack densities, and phloem consumption in trees growing under different stocking. Beetle collections were used to determine emergence across the growing season. Tree mortality data from plots of different densities were used to examine the probability of individual tree infestation. Results: More beetles were caught flying through higher density stands. More attacks were observed in lower stocking stands but there were no differences in the number of insects emerging nor phloem consumption. There was no relationship between tree size and beetle emergence. Peak flight occurred in early to mid-August and only one peak of beetle emergence occurred. The probability of tree attack was influenced by stand stocking and tree diameter. Conclusions: In general, aspects of the biology of MPB in Colorado exhibit similarities and differences with other regions. The data suggest the need to more closely examine how MPB functions in stands of different stocking and how the distribution of tree sizes influence the probability of infestation and extent of mortality in stands. Biological characteristics of MPB in Colorado need further examination, particularly as climate change continues to manifest. Baseline information will be critical to refine management approaches, and extend the understanding of how MPB contributes to shape forest composition and structure in Colorado.

A comparison of accelerated corrosion tests for the assessment of the intergranular corrosion susceptibility of bare 6000 aluminum sheets

Two highly accelerated lab tests, ISO 11846 Method B and PV1113, three cyclic tests, VDA621‐415 (also known as ISO11997 Cycle B), VDA233‐102, and ASTM G85 Annex 2 as well as an accelerated urban outdoor exposure were investigated and compared with respect to their suitability for the evaluation of the IGC susceptibility of bare 6000 aluminum alloys. AA6014 and AA6016, each tested in a low and a high Cu containing variant, suffered, predominantly, intergranular corrosion (IGC) when tested under ISO 11846 and PV1113 conditions. The results obtained by ISO11846 were systematically higher compared to those measured using PV1113. VDA621‐415 (ISO11997 Cycle B) and VDA233‐102 caused only slight localized corrosion, which occurred as IGC, too; however, the density of attack was low. ASTM G85 A2 was the only test that predominantly caused pitting corrosion to occur on all materials.

Gut Bacterial Communities of Dendroctonus valens and Monoterpenes and Carbohydrates of Pinus tabuliformis at Different Attack Densities to Host Pines.

Insects harbor a community of gut bacteria, ranging from pathogenic to obligate mutualistic organisms. Both biotic and abiotic factors can influence species composition and structure of the insect gut bacterial communities. Dendroctonus valens is a destructive forest pest in China. To overcome host pine defenses, beetles mass-attack the pine to a threshold density that can exhaust pine defenses. The intensity of pine chemical defenses and carbohydrate concentrations of pines can be influenced by beetle attack, both of which are known factors that modify beetle’s gut microbiota. However, little is known to what extent variation exists in the beetle’s gut communities, and host monoterpenes and carbohydrates at different attack densities. In this study, the gut bacterial microbiota of D. valens at low and high attack densities were analyzed, and monoterpenes and carbohydrates in host pine phloem were assayed in parallel. The results showed that no significant changes of gut bacterial communities of the beetles and concentrations of D-glucose, D-pinitol, and D-fructose in pine phloem were found between low and high attack densities. The concentrations of α-pinene, β-pinene, limonene at high attack densities were significantly higher than those at low attack densities. Our results suggested that different attack densities of D. valens influence monoterpenes concentration of host pines’ phloem but have no significant impact on gut bacterial community structures of D. valens and carbohydrate concentration of host trees’ phloem in early attack phase. Similar gut bacterial community structures of D. valens between low and high attack densities might be due to the quick adaptation of gut microbiota to high monoterpenes concentrations.

Experimental investigation of generic ice block trajectories under freestream conditions

An experimental database of trajectories featuring idealized, simplified artificial ice blocks under freestream conditions has been created. It includes a variation of key parameters such as the ice block geometry, density, freestream velocity and release angle of attack. The ice block’s position and attitude were optically tracked using a system of two high-speed cameras and a dedicated post-processing routine. The work performed in the scope of the EU co-funded research project STORM aims at the validation and further development of current simulation tools for ice release and ice block trajectories in terms of their ability to cope with the high complexity and randomness of this phenomenon. These tools of different level of fidelity are currently used during the aircraft certification process to estimate the threat of large ice pieces released from the aircraft’s surface impacting into downstream components. The major experimental findings are discussed in this article alongside first promising results from numerical trajectory simulations.

Development of Weeds Density Evaluation System Based on RGB Sensor

Weeds are plant competitors which potentially reduce the yields due to competition for sunlight, water and soil nutrients. Recently, for chemical-based weed control, site-specific weed management that accommodates spatial and temporal diversity of weeds attack in determining the appropriate dose of herbicide based on Variable Rate Technology (VRT) is preferable than traditional approach with single dose herbicide application. In such application, determination of the level of weed density is an important task. Several methods have been studied to evaluate the density of weed attack. The objective of this study is to develop a system that is able to evaluate weed density based on RGB (Red, Green, and Blue) sensors. RGB sensor was used to acquire the RGB values of the surface of the field. An artificial neural network (ANN) model was then used for determining the weed density. In this study the ANN model was trained with 280 training data (70%), 60 validation data (15%), and 60 testing data (15%). Based on the field test, using the proposed method the weed density could be evaluated with an accuracy of 83.75%.

Attack rates of Sirex noctilio and patterns of pine tree defenses and mortality in northern Patagonia.

Accidental and intentional global movement of species has increased the frequency of novel plant-insect interactions. In Patagonia, the European woodwasp, Sirex noctilio, has invaded commercial plantations of North American pines. We compared the patterns of resin defenses and S. noctilio-caused mortality at two mixed-species forests near San Carlos de Bariloche, Argentina. We observed lower levels of resin flow and higher levels of mortality in Pinus contorta compared with Pinus ponderosa. In general, S. noctilio attacked trees with lower resin compared with neighboring trees. Resin production in P. ponderosa was not related to growth rates, but for P. contorta, slower growing trees produced less resin than faster growing conspecifics. For all infested trees, attack density and number of drills (ovipositor probes) per attack did not vary with resin production. Most attacks resulted in one or two drills. Attack rates and drills/attack were basically uniform across the bole of the tree except for a decrease in both drills/attack and attack density in the upper portion of the crown, and an increase in the attack density for the bottom 10% of the tree. Planted pines in Patagonia grow faster than their counterparts in North America, and produce less resin, consistent with the growth-differentiation balance hypothesis. Limited resin defenses may help to explain the high susceptibility of P. contorta to woodwasps in Patagonia.

Semi-natural habitats boost Drosophila suzukii populations and crop damage in sweet cherry

Although increasing landscape complexity is often advocated as a key intervention to sustain pest biocontrol, little is known on how increasing semi-natural habitats surrounding the crop can directly affect the density and damage of generalist pests. Our aim was to test how semi-natural habitats in the landscape influences the density and the impact of spotted wing drosophila (SWD) on sweet cherry. SWD is invasive pest native of South-East Asia that causes severe yield losses in several crops worldwide. We selected 32 conventional cherry orchards in NE Italy surrounded by landscapes with different proportions of forest and we quantified both pest density and crop damage using sentinel fruits. We observed a larger attack density in orchards surrounded by higher forest cover. The same trend was observed for female adult density. Forest habitats may provide ideal microclimatic conditions and alternative host plants that can promote population growth. The effect size of forest cover on both adult density and crop damage, despite the very large tested forest gradient (0–60%), suggests that a reduction of forest cover does not seem to be a viable option for controlling SWD. Indeed, semi-natural habitats can deliver multiple fundamental ecosystem services to the crops (e.g. biocontrol). However, current integrated pest management should take into account landscape composition and interventions should be particularly timely in forested landscapes where SWD can quickly attack the crop at higher density.

Colonization of weakened trees by mass-attacking bark beetles: no penalty for pioneers, scattered initial distributions and final regular patterns.

Bark beetles use aggregation pheromones to promote group foraging, thus increasing the chances of an individual to find a host and, when relevant, to overwhelm the defences of healthy trees. When a male beetle finds a suitable host, it releases pheromones that attract potential mates as well as other ‘spying’ males, which result in aggregations on the new host. To date, most studies have been concerned with the use of aggregation pheromones by bark beetles to overcome the defences of living, well-protected trees. How insects behave when facing undefended or poorly defended hosts remains largely unknown. The spatio-temporal pattern of resource colonization by the European eight-toothed spruce bark beetle, Ips typographus, was quantified when weakly defended hosts (fallen trees) were attacked. In many of the replicates, colonization began with the insects rapidly scattering over the available surface and then randomly filling the gaps until a regular distribution was established, which resulted in a constant decrease in nearest-neighbour distances to a minimum below which attacks were not initiated. The scattered distribution of the first attacks suggested that the trees were only weakly defended. A minimal theoretical distance of 2.5 cm to the earlier settlers (corresponding to a density of 3.13 attacks dm−2) was calculated, but the attack density always remained lower, between 0.4 and 1.2 holes dm−2, according to our observations.

Investigating the Effects of Attack Detection for In-Vehicle Networks Based on Clock Drift of ECUs

As external interfaces of vehicles multiply, information security of an automobile network system has become increasingly troubling. Mounting attacks have raised the attention of researchers to seek optimal solutions. Therefore, they set forth attack detection to demonstrate the vulnerability of in-vehicle networks, yet most of them focus on packet information directly. This paper comprehensively analyzes the vulnerability of in-vehicle networks and investigates a unique detection method based on clock drift of electronic control units. To investigate the applications of the proposed method further, we take attack time and attack density into consideration and present different patterns of two typical attack scenarios, i.e., injecting attack and suspension attack. In addition, we develop a prototype for data acquisition in a controller area network and undertake substantial vehicle experiments. The results show that the attack detection method has advantages in both recognition accuracy and application range compared with the method based on information entropy theory. This research work is expected to contribute to the further development of attacks detection system applied in vehicular networks.

Performance of the tree‐killing bark beetles Ips typographus and Pityogenes chalcographus in non‐indigenous lodgepole pine and their historical host Norway spruce

Abstract The North American lodgepole pine Pinus contorta has been planted on 660 000 ha in Sweden. We compared the performance of Ips typographus and Pityogenes chalcographus in storm‐felled and standing pheromone‐baited trees of the historical host species Norway spruce (Picea abies) and lodgepole pine. In the first summer after a storm, I. typographus colonized 0.2% and P. chalcographus colonized 2.4% of the storm‐felled lodgepole pines compared with 31% and 25%, respectively, of the storm‐felled Norway spruces. In the second summer 1.6% and 41.5% of the lodgepole pines were colonized by I. typographus and P. chalcographus, respectively. The reproductive success of I. typographus was five‐fold higher in Norway spruce than in lodgepole pine. Other species colonizing lodgepole pine were Ips duplicatus, Orthotomicus proximus, Orthotomicus laricis, Monochamus sutor and Pissodes pini. The male attack densities of both bark beetle species required to overcome defences of standing pheromone‐baited trees were much higher in lodgepole pine than in Norway spruce. The reproductive success of I. typographus and P. chalcographus was approximately five‐ and 14‐fold higher, respectively, in Norway spruce than in lodgepole pine. Larvae of the most important groups of bark beetle enemies were present in both storm‐felled and standing pheromone‐baited lodgepole pines colonized by I. typographus and P. chalcographus. In the standing trees, the densities of enemy larvae were lower in lodgepole pine than in Norway spruce, whereas the opposite was true for storm‐felled trees.

The colonisation of Scots pine (Pinus sylvestris L.) by Tomicus minor Hartig in southern Poland: modelling and monitoring

Tomicus minor Hartig (Col., Curculionidae, Scolytinae), occurring on Pinus sylvestris L., is a species which demonstrates high reproductive capability on weakened stands, accelerating the process of forest death. In protected areas, T. minor is regarded as a sensitive bioindicator that reacts to decline in the health and vitality of forests. Although there have been many publications concerning T. minor, no precise method has yet been given for estimating its population so as to enable the monitoring of forest vitality and assessment of the role played by T. minor in the forest ecosystem. The aim of the present work is to develop a statistical method for estimating populations of T. minor, requiring minimum work and interference with the forest ecosystem and permitting the computation of estimation errors. Research was carried out in the years 1992–2011 in pine stands aged over 80 years, growing in a variety of habitats and situated at varying distances from sawmill timber yards. Attack density of T. minor was measured on trap logs made from uninfested living trees. The population of T. minor on the trap logs was described using a multiple linear regression model with two explanatory variables. Among the features investigated, the T. minor population was found to depend significantly on the number of egg galleries on the fifth metre of the trap log counted from the thinner end (p < 0.001) and on the diameter of the trap log in bark at the thinner end (p < 0.05). The model explains approximately 85% (R 2 = 0.8564) of the variation in the total number of T. minor egg galleries on the trap logs. The numbering of units beginning from the thinner end of the log enabled increased precision in determining the model parameter resulting from the concentration of egg galleries on certain units of the log. In all validated plots, the mean real and model values for the number of T. minor egg galleries on the trap logs are similar (p > 0.5), confirming the high accuracy of the developed model.

Pyrrhic victory for bark beetles: Successful standing tree colonization triggers strong intraspecific competition for offspring of Ips sexdentatus

Most bark beetles living on standing trees must overcome the natural resistance of their host to succeed in colonization. For this they perform mass attacks to reach a critical threshold of attack density (CTAD) above which host defences are exhausted. However, this strategy can result in an intense intraspecific competition during larval development. Consequently, the ability of a bark beetle species to sustain outbreaks on standing trees would be conditioned by three key factors: the value of CTAD; the ability of attacking beetles to stop accumulating after CTAD has been reached; and the ability of offspring to tolerate intraspecific competition. To test these hypotheses, we assessed attack and colonization densities of Ips sexdentatus during an outbreak, and estimated CTAD, using a stand-scale approach, in nine maritime pine stands. We also estimated the effect of intraspecific competition on the productivity and fitness of I. sexdentatus offspring, testing increasing rearing densities in the laboratory. The overall CTAD of I. sexdentatus on standing maritime pines was 142 attacks/m2. CTAD varied among stands and ranged from 53 to 177attacks/m2. In several stands, attack densities raised much above local CTAD. Ips sexdentatus exhibited a low tolerance to intraspecific competition. The number of offspring per female and the fitness of emerging adults decreased exponentially with increasing rearing density. Excessive attack densities and negative feedback on offspring quantity and quality are likely to trigger rapid collapse of outbreaks. This supports the prediction that I. sexdentatus is an opportunistically aggressive species.