Beetle Population Dynamics Research Articles

Gene genealogies reveal cryptic species and host preferences for the pine fungal pathogenGrosmannia clavigera

Grosmannia clavigera is a fungal pathogen of pine forests in western North America and a symbiotic associate of two sister bark beetles: Dendroctonus ponderosae and D.jeffreyi. This fungus and its beetle associate D.ponderosae are expanding in large epidemics in western North America. Using the fungal genome sequence and gene annotations, we assessed whether fungal isolates from the two beetles inhabiting different species of pine in epidemic regions of western Canada and the USA, as well as in localized populations outside of the current epidemic, represent different genetic lineages. We characterized nucleotide variations in 67 genomic regions and selected 15 for the phylogenetic analysis. Using concordance of gene genealogies and distinct ecological characteristics, we identified two sibling phylogenetic species: Gc and Gs. Where the closely related Pinus ponderosa and P.jeffreyi are infested by localized populations of their respective beetles, Gc is present. In contrast, Gs is an exclusive associate of D.ponderosae mainly present on its primary host-tree P.contorta; however, in the current epidemic areas, it is also found in other pine species. These results suggest that the host-tree species and the beetle population dynamics may be important factors associated with the genetic divergence and diversity of fungal partners in the beetle-tree ecosystems. Gc represents the original G.clavigera holotype, and Gs should be described as a new species.

Population size and dispersal ofSulcophanaeus leander(Coleoptera: Scarabaeidae) on riverine beaches in the Amazonian region

Dung beetles are a well-defined guild within the family Scarabaeidae, with distinctive morphological, ecological and behavioural characteristics (Halffter & Matthews 1966). Although this group has been extensively studied (Hanski & Cambefort 1991) due in part to the important role they fulfil in ecosystems (Nicholset al. 2008), little information exists regarding population size and the scale of their dispersal abilities, especially in the Neotropical region. Moreover, few studies have been devoted to exploring the population dynamics of dung beetles (Roslin 1999, 2000).

Bark beetles in the Tatra Mountains. International research 1998– 2005 – an overview

This paper is a review of fundamental information on bark beetles and their interactions with several predisposing factors (air pollution, drought/temperature interactions, windthrows, management activities) that are thought to contribute to the outbreaks in the High Tatra Mountains. The findings of many research projects indicate that the impact of air pollution on bark beetle populations is indirect and complex and that the disturbances in the physiology and natural resistance of trees may be of crucial importance to bark beetle population dynamics. An active forest protection approach is needed to be applied to the secondary Norway spruce forests affected in the past by human activity. Bark beetle populations in natural and near-natural forests (mainly in the upper montane zone) are regulated by natural mechanisms; bark beetles are therefore a natural factor contributing to forest development, including the transition of future generations of spruce.

Lethal and sub‐lethal effects of ivermectin on north temperate dung beetles,Aphodius aterandAphodius rufipes(Coleoptera: Scarabaeidae)

Abstract. 1. Ivermectin is an anthelmintic veterinary medicine, and is excreted in the dung of treated livestock in a mainly unmetabolised form. Ivermectin is known to have toxic effects on dung beetles, but most studies to date have been conducted on tropical and sub‐tropical species. Relatively few laboratory studies have focused on the specific effects of ivermectin on survival and development of north temperate dung beetles.2. In this study, we experimentally investigated the effect of ivermectin concentration on various life stages of twoAphodiusdung beetle species. Dung was collected from cattle groups that had been treated with a subcutaneous injection of ivermectin. Laboratory bioassays were conducted by feeding adults of two beetle species (Aphodius aterandAphodius rufipes) with dung that contained different concentrations of ivermectin. Adult survival and oviposition were measured, and the subsequent development and survival of produced larvae was monitored over time.3. Larval development rates were significantly slowed by ivermectin. Ivermectin had significant negative effects on the survival of larvae. Overall, ivermectin concentration caused large and significant reductions in the cohort size from an individual dung pat that would potentially contribute to the next generation of beetles.4. In general, ivermectin concentration did not have significant negative effects on adult survival. The number of eggs per femaleA. rufipeswas significantly reduced by ivermectin concentration in one of two bioassays, but the magnitude of the effect was not large. The actual impacts on dung beetle population dynamics in farmland would depend on several other factors, which are discussed.

Seasonal population dynamics of small hive beetles, Aethina tumida Murray, in the south-eastern USA

SummaryThe population of small hive beetles, Aethina tumida (SHB), was monitored from 2005 to 2008 in colonies of Italian and Russian honey bees located near St. Gabriel, Louisiana, USA. SHB populations differed between honey bee strains (only in one site out of two), with Italian colonies supporting more beetles (7.45 ± 0.98 SHB per colony) than the Russian colonies (4.48 ± 0.51 SHB per colony). No difference between the two strains was observed at site 1 where the SHB population was generally low (Italian = 2.73 ± 0.36 SHB; Russian = 2.69 ± 0.57 SHB per colony). Our results also revealed that SHB populations varied throughout the year, with peak infestations observed in the autumn (September and November). SHB abundance was significantly correlated with the proportion of hot days, but not with the proportions of cool, dry, or humid days, or the percentage of days with rainfall. Our results suggest that in-hive autumn trapping of SHB in the south eastern USA may reduce springtime numbers of SHB.

The influence of habitat type on the population dynamics of ground beetles (Coleoptera: Carabidae) in marshland

This study presents qualitative and quantitative research on communities of ground beetles (Carabidae) occurring in 2001 and 2003 in three types of habitats located near Bydgoszcz city, Poland (UTM CD19), on the Vistula river floodplain: elm and ash riparian forest (RF), poplar monoculture (P), and unintensively-farmed meadows (M). During both studied years 57 species of ground beetles were found in riparian forests (RF), 56 species in plot P and 47 in plot M. In 2001 from all sample plots 3845 beetles were collected; in 2003- 9589. In both years most specimens came from plot RF (3123 in 2001 and 6224 in 2003). From plot P 2656 specimens of ground beetles were collected and from plot M 1430 specimens. Statistically significant differences were found in the abundance of Carabidae, among sampling areas and the years of study.

Responses of a specialist and a generalist seed predator to variation in their common resource

Fluctuations of resources in time and space will influence not only species abundance but also interactions among species. For plant–consumer interactions, the effects of resource variation have mostly been studied in systems with high resource variability. Systems with moderate variations are less studied, although ecological and evolutionary dynamics of plants and consumers are likely to be affected also by less extreme variability. The effects of variation in a particular resource should depend on consumer diet width.We examined how spatial and temporal variation in seed production in the perennial herb Lathyrus vernus influenced population dynamics and resource utilization in two beetle pre‐dispersal seed predators with different host ranges over six years. The monophagous Apion opeticum occupied fewer patches and had lower densities than the oligophagous Bruchus atomarius. The proportion of seeds attacked increased with increases in seed production between years for both seed predators. A possible explanation for these patterns is that population dynamics of beetles are driven largely by local factors and that the same factors influence both beetle performance and seed production. In B. atomarius, patterns may also be influenced by a more pronounced preference for L. vernus in years with a high seed production in L. vernus. We conclude that relatively modest variation in seed production may result in responses that differ in both direction and extent from those usually observed in systems with high variation in seed production.

Modeling the Impacts of Two Bark Beetle Species Under a Warming Climate in the Southwestern USA: Ecological and Economic Consequences

Predicted climate warming is expected to have profound effects on bark beetle population dynamics in the southwestern United States. Temperature-mediated effects may include increases in developmental rates, generations per year, and changes in habitat suitability. As a result, the impacts of Dendroctonus frontalis and Dendroctonus mexicanus on forest resources are likely subject to amplification. To assess the implications of such change, we evaluated the generations per year of these species under three climate scenarios using a degree-day development model. We also assessed economic impacts of increased beetle outbreaks in terms of the costs of application of preventative silvicultural treatments and potential economic revenues forgone. Across the southwestern USA, the potential number of beetle generations per year ranged from 1-3+ under historical climate, an increase of 2-4+ under the minimal warming scenario and 3-5+ under the greatest warming scenario. Economic benefits of applying basal area reduction treatments to reduce forest susceptibility to beetle outbreaks ranged from $7.75/ha (NM) to $95.69/ha (AZ) under historical conditions, and $47.96/ha (NM) to $174.58/ha (AZ) under simulated severe drought conditions. Basal area reduction treatments that reduce forest susceptibility to beetle outbreak result in higher net present values than no action scenarios. Coupled with other deleterious consequences associated with beetle outbreaks, such as increased wildfires, the results suggest that forest thinning treatments play a useful role in a period of climate warming.

Spatial–temporal analysis of species range expansion: the case of the mountain pine beetle,Dendroctonus ponderosae

AbstractAim The spatial extent of western Canada’s current epidemic of mountain pine beetle,Dendroctonus ponderosaeHopkins (Coleoptera: Curculionidae, Scolytinae), is increasing. The roles of the various dispersal processes acting as drivers of range expansion are poorly understood for most species. The aim of this paper is to characterize the movement patterns of the mountain pine beetle in areas where range expansion is occurring, in order to describe the fine‐scale spatial dynamics of processes associated with mountain pine beetle range expansion.Location Three regions of Canada’s Rocky Mountains: Kicking Horse Pass, Yellowhead Pass and Pine Pass.Methods Data on locations of mountain pine beetle‐attacked trees of predominantly lodgepole pine (Pinus contortavar.latifolia) were obtained from annual fixed‐wing aircraft surveys of forest health and helicopter‐based GPS surveys of mountain pine beetle‐damaged areas in British Columbia and Alberta. The annual (1999–2005) spatial extents of outbreak ranges were delineated from these data. Spatial analysis was conducted using the spatial–temporal analysis of moving polygons (STAMP), a recently developed pattern‐based approach.Results We found that distant dispersal patterns (spot infestations) were most often associated with marginal increases in the areal size of mountain pine beetle range polygons. When the mountain pine beetle range size increased rapidly relative to the years examined, local dispersal patterns (adjacent infestation) were more common. In Pine Pass, long‐range dispersal (> 2 km) markedly extended the north‐east border of the mountain pine beetle range. In Yellowhead Pass and Kicking Horse Pass, the extension of the range occurred incrementally via ground‐based spread.Main conclusions Dispersal of mountain pine beetle varies with geography as well as with host and beetle population dynamics. Although colonization is mediated by habitat connectivity, during periods of low overall habitat expansion, dispersal to new distant locations is common, whereas during periods of rapid invasion, locally connected spread is the dominant mode of dispersal. The propensity for long‐range transport to establish new beetle populations, and thus to be considered a driver of range expansion, is likely to be determined by regional weather patterns, and influenced by local topography. We conclude that STAMP appears to be a useful approach for examining changes in biogeograpical ranges, with the potential to reveal both fine‐ and large‐scale patterns.

Effects of Gallery Density and Species Ratio on the Fitness and Fecundity of Two Sympatric Bark Beetles (Coleoptera: Curculionidae)

Interspecific interactions among tree-killing bark beetle species may have ecologically important consequences on beetle population dynamics. Using two tree-killing beetle species (Dendroctonus brevicomis and D. frontalis), we performed observational and experimental studies to verify cross-attraction and co-colonization under field conditions in northern Arizona and test the effects of gallery density and species ratio on response variables of average gallery length, offspring size (progeny fitness), and offspring production per centimeter gallery (fecundity). Our results show that both D. frontalis and D. brevicomis aggregate to pheromones synthesized de novo by D. brevicomis under field conditions and that galleries of both D. brevicomis and D. frontalis occurred together in the same region of a single host tree with significant frequency. In experimental manipulations of species ratios, the presence of conspecific beetles in the gallery environment strongly mediated fecundity, but D. frontalis was the only species that suffered negative impacts from the presence of heterospecific beetles in the gallery environment. Interactions did not result in any apparent fitness effects for progeny of either species, which suggests that multispecies aggregations and co-colonization may be a dominant ecological strategy in the region and result in niche sharing.

A dynamic host selection model for mountain pine beetle, Dendroctonus ponderosae Hopkins

The link between individual habitat selection decisions (i.e., mechanism) and the resulting population distributions of dispersing organisms (i.e., outcome) has been little-studied in behavioural ecology. Here we consider density-dependent habitat (i.e., host) selection for an energy- and time-limited forager: the mountain pine beetle ( Dendroctonus ponderosae Hopkins). We present a dynamic state variable model of individual beetle host selection behaviour, based on an individual’s energy state. Field data are incorporated into model parameterization which allows us to determine the effects of host availability (with respect to host size, quality, and vigour) on individuals’ decisions. Beetles choose larger trees with thicker phloem across a larger proportion of the state-space than smaller trees with thinner phloem, but accept lower quality trees more readily at low energy- and time-states. In addition, beetles make habitat selection decisions based on host availability, conspecific attack densities, and beetle distributions within a forest stand. This model provides a framework for the development of a spatial game model to examine the implications of these results for attack dynamics of beetle populations.

Multi-temporal analysis of high spatial resolution imagery for disturbance monitoring

Mountain pine beetle red attack damage has been successfully detected and mapped using single-date high spatial resolution (< 4 m) satellite multi-spectral data. Forest managers; however, need to monitor locations for changes in beetle populations over time. Specifically, counts of individual trees attacked in successive years provide an indication of beetle population growth and dynamics. Surveys are typically used to estimate the ratio of green (current) attack trees to red (previous) attack trees or G:R. In this study, we estimate average stand-level G:R using a time-series of QuickBird multi-spectral and panchromatic satellite data, combined with field data for three forested stands near Merritt, British Columbia, Canada. Using a ratio of QuickBird red to green wavelengths (Red–Green Index or RGI), the change in RGI (ΔRGI) in successive image pairs is used to estimate red attack damage in 2004, 2005, and 2006, with true positive accuracies ranging from 89 to 93%. To overcome issues associated with differing viewing geometry and illumination angles that impair tracking of individual trees through time, segments are generated from the QuickBird multi-spectral data to identify small groups of trees. These segments then serve as the vehicle for monitoring changes in red attack damage over time. A local maxima filter is applied to the panchromatic data to estimate stem counts, thereby allowing an indication of the total stand population at risk of attack. By combining the red attack damage estimates with the local maxima stem counts, predictions are made of the number of attacked trees in a given year. Backcasting the current year's red attack damaged trees as the previous year's green attack facilitates the estimation of an average stand G:R. In this study area, these retrospective G:R values closely match those generated from field surveys. The results of this study indicate that a monitoring program using a time series of high spatial resolution remotely sensed data (multi-spectral and panchromatic) over select sample locations, could be used to estimate G:R over large areas, facilitating landscape level management strategies and/or providing a mechanism for assessing the efficacy of previously implemented strategies.

Influence of Elevation on Bark Beetle (Coleoptera: Curculionidae, Scolytinae) Community Structure and Flight Periodicity in Ponderosa Pine Forests of Arizona

We examined abundance and flight periodicity of five Ips and six Dendroctonus species (Coleoptera: Curculionidae, Scolytinae) among three different elevation bands in ponderosa pine (Pinus ponderosa Douglas ex. Lawson) forests of northcentral Arizona. Bark beetle populations were monitored at 10 sites in each of three elevation bands (low: 1,600-1,736 m; middle: 2,058-2,230 m; high: 2,505-2,651 m) for 3 yr (2004-2006) using pheromone-baited Lindgren funnel traps. Trap contents were collected weekly from March to December. We also studied temperature differences among the elevation bands and what role this may play in beetle flight behavior. Bark beetles, regardless of species, showed no consistent elevational trend in abundance among the three bands. The higher abundances of Ips lecontei Swaine, I. calligraphus ponderosae Swaine, Dendroctonus frontalis Zimmerman, and D. brevicomis LeConte at low and middle elevations offset the greater abundance of I. knausi Swaine, D. adjunctus Blandford, D. approximatus Dietz, and D. valens LeConte at high elevations. I. pini (Say) and I. latidens LeConte were found in similar numbers across the three bands. Flight periodicity of several species varied among elevation bands. In general, the flight period shortened as elevation increased; flight initiated later and terminated earlier in the year. The timing, number, and magnitude of peaks in flight activity also varied among the elevation bands. These results suggest that abundance and flight seasonality of several bark beetles are related to elevation and the associated temperature differences. The implications of these results are discussed in relation to bark beetle management and population dynamics.

Dietary Benefits of Fungal Associates to an Eruptive Herbivore: Potential Implications of Multiple Associates on Host Population Dynamics

We used the mountain pine beetle (Dendroctonus ponderosae Hopkins) and its two fungal associates, Grosmannia clavigera and Ophiostoma montium, to study potential nutritional benefits of fungi to bark beetles. We tested for potential effects of feeding on phloem colonized by fungi on beetle performance in field and laboratory studies. The fungi increased nitrogen levels in the phloem of attacked trees by 40%, indicating that it may be an important source of dietary nitrogen for mountain pine beetles. However, nitrogen levels of phloem inoculated with fungi in the laboratory were similar to uncolonized phloem, indicating that the fungi may redistribute nitrogen from the sapwood to the phloem rather than increase absolute levels of nitrogen. Beetles emerging from attacked trees carrying G. clavigera were larger than beetles carrying O. montium, which in turn were larger than beetles lacking fungi. Results of experimental laboratory studies varied, likely because of differences in the growth and sporulation of fungi under artificial conditions. Results indicate that the two fungi may offer complementary benefits to the mountain pine beetle because larvae preferentially fed on phloem colonized by both fungi together over phloem colonized by one fungus or uncolonized phloem. Teneral adults preemergence fed on spores in pupal chambers when they were produced and consumed little phloem before emerging. Teneral adults mined extensively in the phloem before emerging when spores were not produced in the pupal chamber. Our results provide evidence for a nutritional role of fungi in the diet of bark beetles and show that multiple associates may differentially affect beetle performance, which could have important implications for bark beetle population dynamics.

Dietary Benefits of Fungal Associates to an Eruptive Herbivore: Potential Implications of Multiple Associates on Host Population Dynamics

We used the mountain pine beetle (Dendroctonus ponderosae Hopkins) and its two fungal associates, Grosmannia clavigera and Ophiostoma montium, to study potential nutritional benefits of fungi to bark beetles. We tested for potential effects of feeding on phloem colonized by fungi on beetle performance in field and laboratory studies. The fungi increased nitrogen levels in the phloem of attacked trees by 40%, indicating that it may be an important source of dietary nitrogen for mountain pine beetles. However, nitrogen levels of phloem inoculated with fungi in the laboratory were similar to uncolonized phloem, indicating that the fungi may redistribute nitrogen from the sapwood to the phloem rather than increase absolute levels of nitrogen. Beetles emerging from attacked trees carrying G. clavigera were larger than beetles carrying O. montium, which in turn were larger than beetles lacking fungi. Results of experimental laboratory studies varied, likely because of differences in the growth and sporulation of fungi under artificial conditions. Results indicate that the two fungi may offer complementary benefits to the mountain pine beetle because larvae preferentially fed on phloem colonized by both fungi together over phloem colonized by one fungus or uncolonized phloem. Teneral adults preemergence fed on spores in pupal chambers when they were produced and consumed little phloem before emerging. Teneral adults mined extensively in the phloem before emerging when spores were not produced in the pupal chamber. Our results provide evidence for a nutritional role of fungi in the diet of bark beetles and show that multiple associates may differentially affect beetle performance, which could have important implications for bark beetle population dynamics.

Individual and Population Effects of Eugregarine, &lt;I&gt;Gregarina niphandrodes&lt;/I&gt; (Eugregarinida: Gregarinidae), on &lt;I&gt;Tenebrio molitor&lt;/I&gt; (Coleoptera: Tenebrionidae)

Gregarines are single-celled parasites in the phylum Apicomplexa that infect invertebrates. They are highly abundant on three levels: among a large diversity of invertebrates, in the proportion of population of organisms they infect, and within individually infected organisms. Because of their remarkable prevalence, we hypothesize that they play an important role in support of their hosts. However, studies done to date on the impact of gregarines on their host are conflicting. Therefore, we studied the impact of gregarines on their host using a model Gregarina niphandrodes infection in Tenebrio molitor. The impact of infection was measured by comparing beetles with no or low infection to those with artificially induced high infection. The numbers of individuals in each of the three easily visible developmental stages of the T. molitor (larva, pupa, and adult) were censused weekly. From these observations, fertilities and probabilities of survival with transition between stages were estimated. These estimated vital rates were used to construct a stage-classified projection matrix model. We also measured the longevity of individual beetles with low and high infection that were grown in isolation. The results indicate that there is no significant difference in the population dynamics of beetles with low and high infection. However, the longevity was significantly different between beetles with low infection than the deliberately highly infected group.

Population dynamics of Chaetocnema tibialis Illiger and Phyllotreta vittula (Redtenbacher) on the weed Amaranthus retroflexus L. and cultivated Amaranthus caudatus L.

In 1995–1997, the population dynamics of the flea beetles &lt;i&gt;Chaetocnema tibialis and &lt;i&gt;Phyllotreta vittula&lt;/i&gt;, associated with &lt;i&gt;Amaranthus retroflexus&lt;/i&gt; (wild species) and &lt;i&gt;Amaranthus caudatus&lt;/i&gt; (cultivated species), were studied at the locality Nitra-Malanta (48°19'N, 18°09'E) in south-western Slovakia. On both plant species, the number of &lt;i&gt;C. tibialis&lt;/i&gt; adults was usually very low until the beginning of July. During July the number of &lt;i&gt;C. tibialis&lt;/i&gt; increased, but sooner on cultivated amaranth. An increased number of &lt;i&gt;C. tibialis&lt;/i&gt; adults was observed on both amaranth species until the middle of September. The results showed that amaranth plants are a very important reservoir of &lt;i&gt;C. tibialis&lt;/i&gt; during summer. &lt;i&gt;P. vittula&lt;/i&gt; was a common flea beetle on amaranth during the whole summer, but its numbers never exceeded more than 10 adults per 25 plants. Low temperatures in winter had a negative effect on populations of &lt;i&gt;C. tibialis&lt;/i&gt; on both amaranth species and also on populations of &lt;i&gt;P. vittula&lt;/i&gt; on &lt;i&gt;A. retroflexus&lt;/i&gt;. The lower the precipitation was in July, the higher were the populations of &lt;i&gt;C. tibialis&lt;/i&gt; on both amaranth species and the populations of &lt;i&gt;P. vittula&lt;/i&gt; on &lt;i&gt;A. retroflexus&lt;/i&gt;.

A RESOURCE-DEPLETION MODEL OF FOREST INSECT OUTBREAKS

Detailed analyses of thresholded ecological interactions can improve our understanding of the transition from aperiodic to periodic dynamics. We develop a threshold model of the population dynamics of outbreaking bark beetle populations that alternate between non-epidemic and epidemic behavior. The model involves accumulation of resources during low-density periods and depletion during outbreaks. The transition between the two regimes is caused by disturbance events in the form of major tree felling by wind. The model is analyzed with particular reference to the population dynamics of the spruce bark beetle (Ips typographus) in Scandinavia for which a comprehensive literature allows full parameterization. The fairly constant outbreak lengths and the highly variable waiting time between outbreaks that are seen in the historical records of this species agree well with the predictions of the model. The thresholded resource-depletion dynamics result in substantial variation in the degree of periodicity between stochastic realizations. The completely aperiodic tree colonizations are partly predictable when the timing of the irregular windfall events are known. However, the predictability of inter-outbreak periods is low due to the large variation of cases falling most frequently in the middle between the extremes of purely nonperiodic (erratic) and periodic (cyclic) fluctuations.

Seasonal Dynamics of Mites and Fungi and Their Interaction with Southern Pine Beetle

We evaluated whether Dendroctonus frontalis Zimmermann populations were influenced by nontrophic interactions involving commensal mites, their mutualistic bluestain fungus Ophiostoma minus (Hedgc.) H. and P. Sydow, and beetle-mutualistic mycangial fungi. We tested for effects of delayed, nonlinear, or positive feedback from O. minus and mites on D. frontalis population growth. We predicted that (1) high mite densities have demographic consequences for beetles by influencing the prevalence of O. minus and antagonistic interactions between O. minus and mycangial fungi, and (2) inter-relations and abundances of mites and fungi differentially vary throughout the year in a seasonally variable climate. Surveys of D. frontalis populations revealed that temporal and spatial patterns in abundance of mites and their mutualistic fungus, O. minus were inversely related with beetle population growth. Negative demographic effects of O. minus on D. frontalis were nonlinear, only affecting beetle per capita reproduction when fungi colonized >35% of phloem habitat. Mite abundance was strongly correlated with O. minus and was an important driving force in promoting bluestain prevalence within trees. Spring abundances of mites and the prevalence of O. minus during D. frontalis infestation formation were strong predictors of beetle population decline later that year. The two mutualistic fungi associated with D. frontalis cycled seasonally but did not seem to influence beetle population dynamics.

Size and shape changes of Ips typographus L. (Coleoptera: Scolytinae) in relation to population level

Abstract1 High intraspecific competition is known to occur during Ips typographus outbreaks, and is thought to be the main factor regulating epidemic populations by affecting beetle population productivity. However, little is known about the consequences of intraspecific competition on population quality during outbreaks, although it could have consequences on beetle population dynamics.2 Ips typographus morphological variations among localities, years and beetle population levels were investigated in 10 Norway spruce (Picea abies) stands having various beetle damage intensities. Beetle size and shape estimators based on wing length, and using isometric size and log‐shape ratios, were employed. Field‐caught beetles were compared with beetles emerging from controlled breeding at different densities, performed in the laboratory. Beetles from this colony were also used to check the influence of breeding densities on the size estimator.3 Size variations occurred among localities and years and were consistent with the epidemic or latent status of the beetle populations. Controlled breeding confirmed the negative effect of beetle densities encountered in the field on offspring size. Two hypotheses are formulated to explain this increase of intraspecific competition during an outbreak, but our data support the effect of host quality change between latent and epidemic populations.4 Shape variations also occurred among localities but were unrelated to beetle population levels. No groups consistent with a geographical structure were found, suggesting low genetic variation for I. typographus populations in France.