Plasticity in life-history traits of the bark beetle Ips calligraphus as influenced by phloem thickness

Summary Reproduction and development of Ips calligraphus (Germar) (Coleoptera: Scolytidae) occur primarily in the phloem (inner bark) tissue of its pine hosts. In slash pine (Pinus elliottii Engelm. var. elliottii), phloem thickness can vary widely from tree to tree. We compared adult residence time and fecundity and progeny development time, body size, and sex ratio of this beetle when reared in slash pine bolts and bark slabs with phloem thicker or thinner than average adult body width. Most studies were conducted at 20°, 25°, and 30° C. Residence time of parent males and females decreased with increasing temperature but it was not affected by phloem thickness. Residence time of parent males was about 2 days shorter than that of parent females at each temperature. Reproductive fitness was greater in thick phloem at all temperatures as measured by faster larval development, earlier emergence of progeny (F ₁ ) adults, and emergence of more progeny adults per parent female. Progeny survival was similar between phloem those from thick phloem, and their sex ratio was female biased (1:2 vs 1:1, male:female). When allowed to inhabit thick phloem, the progeny (F ₂) of adults from thin phloem were just as large and of similar sex ratio (1:1) as were progeny of F ₁ adults from thick phloem. The high degree of plasticity in the life-history traits of this beetle may enable it to successfully colonize pines that vary widely in phloem thickness.     

Ultrastructural study of the microsporidian chytridiopsis typographi (Chytridiopsida: Microspora) infecting the bark beetle,Ips typographus (Scolytidae: Coleoptera), with new data on spore dimorphism

Two types of sporogony of the microsporidian Chytridiopsis typographi in the midgut of adult bark beetle, Ips typographus, have been examined by means of light and electron microscopy. New data are reported on spore dimorphism and on the formation of pansporoblasts in two types of sporogony. Thin-walled spores, larger in size, are formed in a parasitophorous vacuole in the host columnar cells. Thick-walled spores are formed in a minimal vacuole in the host. The ultrastructure of the spore walls and the cyst wall are different from the organization in other microsporidia. Both spore types have identical internal structures and viable spores.     

Flight propensity and diapause incidence in five populations of the bark beetle Ips typographus in Scandinavia

Emergence from brood logs, take-off activity and the duration of tethered flight was recorded in the first laboratory generation of the bark beetle Ips typographus L. (Coleoptera: Scolytidae) from five locations (ca 300 km apart) in Sweden and Denmark. Beetles of northerly origin emerged later from brood logs. This pattern was associated with an increasing proportion on non-fliers towards the north. After overwintering, both the rate of development of flight activity and the proportion of non-fliers were the same among populations. Flight duration of fliers was similar among populations and appeared unaffected by outbreak conditions.     

Gallery construction and oviposition of the bark beetle Ips typographus (Coleoptera: Scolytidae) at different breeding densities

Abstract. 1. The bole of a Norway spruce, Picea abies (L.) Karst., was cut in 25 cm sections and infested in the laboratory with 2 or 8 females/dm² of Ips typographus (L.) and an equal number of males.
2. One log of each beetle density was dissected every second day, beginning 2 days after female introduction.
3. The oviposition rate was highest at the beginning of the breeding period for both densities and then declined, especially at the high density. Residence time is a useful approximation for the number of laid eggs in the beginning of the oviposition period or when the density is low.
4. Final gallery length and egg number per gallery were on average significantly smaller at density 8 than at density 2.
5. Linear relationships between total gallery length and number of egg niches were found to be similar for the two densities.
6. An estimate of the egg to adult mortality at different densities was found by using data from a field study that related gallery length to breeding density in attacked living trees, together with published relationships between density and egg niches or emergence of new adults.
7. It was concluded that both decreased oviposition rate and earlier re-emergence at higher densities contribute to a declining oviposition with increasing density. The final offspring production is futher reduced by lower survival due to larval competition as density increases.     

Variation in the mating system of oribi and its ecological determinants

Flexibility (varying from monogamy in South Africa to polygyny in East Africa) has been documented in the mating system of the oribi ( Ourebia ourebi ) by several authors. To investigate this, a population was studied in Northern KwaZulu-Natal (South Africa). The adult sex ratio was one male to 1.38 females and the mean group size was 2.1 (n = 13). Although monogamous and polygynous groups occurred in the study population, the polygynous groups were unstable and depended on seasonal food abundance. Comparison of oribi populations across Africa suggests that variation in the mating system is determined mainly by predation risk and altitude (most likely through its effect on graze quality). In areas of high predation risk, oribi can survive only when resource quality permits females to forage in groups, thereby allowing males to be polygynous.     

Response of the whitespotted sawyer beetle, Monochamus s. scutellatus, and associated woodborers to pheromones of some Ips and Dendroctonus bark beetles

The response of whitespotted sawyer beetle, Monochamus s. scutellatus, to pheromones of the bark beetles, Dendroctonus rufipennis, Ips pini, Ips perturbatus and Ips latidens, and α‐pinene was investigated with field‐trapping experiments. Traps baited with ipsenol caught significantly more M. s. scutellatus than unbaited traps, whereas the other compounds (ipsdienol, ipsdienol plus lanierone, ipsdienol plus cis‐verbenol or frontalin) did not. Combining α‐pinene with ipsdienol, ipsdienol plus lanierone, ipsdienol plus cis‐verbenol or with frontalin did not increase captures of M. s. scutellatus above those of α‐pinene alone, whereas the combination of α‐pinene with ipsenol did. When α‐pinene was combined with ipsdienol or frontalin, trap captures of Monochamus mutator were significantly higher than unbaited traps or traps baited with frontalin but were not higher than traps baited with α‐pinene. The combination of ipsenol and α‐pinene was significantly more attractive to Monochamus notatus than unbaited traps; however, traps containing either ipsenol or α‐pinene were as attractive as the combination. None of the species of Buprestidae (Buprestis maculativentris and Chalcophora virginiensis) responded significantly to any of the treatments.     

Control of pheromone production in the bark beetle, Ips cembrae

ABSTRACT. Exposure of newly emerged Ips cembrae adults to myrcene vapour resulted in the production of ipsenol and ipsdienol by males, in quantities comparable to those found during natural attack of larch trees. Treatment of male beetles with juvenile hormone analogue (JHA) triggered production of 3-mefhyl-3-buten-l-ol, the third component of the aggregation pheromone complex. The beetles are therefore capable of producing ipsenol and ipsdienol immediately upon contact with host resin, whereas methylbutenol production appears to be hormonally controlled upon the initiation of feeding. Beetles exposed to the enantiomers of ipsdienol apparently utilized only (R)-(—) ipsdienol to synthesize ipsenol, suggesting a high degree of chiral selectivity.     

Temperature‐dependent development of the European larch bark beetle,Ips cembrae

The temperature‐dependent development of the European larch bark beetle, Ips cembrae, was studied under long‐day conditions L:D 16:8 at three temperature regimes, 15°C, 20°C and 25°C, using the sandwich plate method. By observing the individual developmental progress, we calculated the developmental times and lower developmental thresholds of one entire generation and various ontogenetic stages. The mean developmental time of one generation was about 120, 64 and 37 days at 15°C, 20°C and 25°C, respectively. The egg stage comprised about 9% of the total development or about 16% of the pre‐imaginal development. The larval stages took about 39% of the entire and about 66% of the pre‐imaginal development. The pupal stage needed about 11% of the total or about 18% of the pre‐imaginal development. The lower developmental threshold for one generation was 11.2°C. The egg stage had the highest lower developmental threshold of 12.0°C, the pupa the lowest of 9.8°C and the total larval stages showed a value of 11.2°C. The thermal requirements for I. cembrae have never been studied in detail before. The results will be a valuable contribution for monitoring and risk assessment models to estimate the beetle's phenology and its potential impacts on forest ecosystems under changing climate conditions.     

The bark beetle Pityogenes chalcographus (L.) (Scolytidae) in living trees: reproductive success, tree mortality and interaction with Ips typographus

Abstract:  Tree-killing ability of Pityogenes chalcographus was experimentally investigated by baiting living spruce Picea abies with synthetic aggregation pheromone, thereby exposing them to beetle attack. Reproductive success was estimated by rearing beetles from stem sections taken from killed trees. The presence of Ips typographus on several killed trees allowed a comparison of reproductive success in the presence and absence of this species. Furthermore, the possibility that breeding material colonized by P. chalcographus may induce subsequent attacks by I. typographus on nearby trees was also studied. The tree killing ability of P. chalcographus was low as only 8% of the baited trees, attacked by P. chalcographus alone, were killed. Tree death was strongly related to the presence of I. typographus , which is in line with the association with aggressive wood-living fungi in this species. The reproductive success was low, with on average less than one daughter beetle produced per mother beetle. The success was significantly higher in trees also inhabited by I. typographus . Tree-parts colonized by P. chalcographus induced almost no attacks by I. typographus on nearby trees.     

Pathogens of the bark beetle Ips cembrae: microsporidia and gregarines also known from other Ips species

The objective of the current study was to identify pathogens of the large larch bark beetle, Ips cembrae, which is a secondary pest that has produced several local outbreaks across Europe in recent years. Beetles were collected from pheromone traps, trap trees and emergence traps (Larix decidua) during 2007 to 2011 at 10 study sites in central Europe. A total of 3379 mature and callow beetles were examined with a light microscope, and only two microsporidian pathogens [Chytridiopsis typographi and a diplokaryotic microsporidium (probably Nosema sp.)] and two gregarines (Gregarina typographi and Mattesia schwenkei) were found. Within the I. cembrae populations, the infection rate for C. typographi ranged from 2 to 58%. Nosema sp. occurred in only two beetles in 2007 (at two study sites). G. typographi was recorded only in Austria and Croatia and only in 1–2% of the beetles in those countries. Mattesia schwenkei was observed solely in Croatia in 0.6% of the beetles in that country. Only one fungal pathogen in the genus Fusarium was found and only in two mature beetles (0.7%) in 2010. The pathogen species found during our study of I. cembrae were very similar to the pathogens previously identified for Ips typographus. No species‐specific pathogen was detected.     

Multiple component system of sugars and polyols in the overwintering spruce bark beetle, Ips typographus

Overwintering adults of the spruce bark beetle, Ips typographus (L.) showed an unusually complex sugar/polyol cryoprotectant system. The major components of the multiple system were: glucose (177.6 mmolL(-1), March); trehalose (175.0 mmolL(-1), December); sorbitol (147.9 mmolL(-1), January); mannitol (81.2 mmolL(-1), March); and erythritol (40.7mmolL(-1), March) (in the parentheses, the maximum concentrations are shown and the month when they were reached). Other minor components were glycerol, fructose, threitol, myo-inositol, arabinitol and ribitol. Distinct seasonal patterns of accumulation/depletion in various components were found. Glycerol, trehalose and glucose started to accumulate first, during early autumn, when the air temperatures fluctuated between 20 and 0 degrees C, and diapause beetles continued in feeding. Glycerol was depleted, glucose remained stable and trehalose continued in accumulation during late autumn when the temperatures oscillated around 0 degrees C. During early winter severe frosts reaching -20 degrees C came, the beetles terminated their diapause and trehalose was partially depleted, while mannitol, sorbitol, fructose, threitol and erythritol started to accumulate. Cold weather continued also during late winter when the beetles remained quiescent. During this period, trehalose was re-accumulated, threitol and erythritol continued to increase, mannitol remained stable and sorbitol, fructose decreased. All cryoprotectans were finally cleared in the beetles which were spontaneously leaving bark during early spring. The seasonal maximum of total concentration of all cryoprotectants (578.2 mOsmol L(-1)) was reached in March. Such a concentration results in colligative depression of melting point of body fluids down by 1.08 degrees C only. It suggests that the potential cryoprotective effect of accumulated sugars and polyols was related rather to their non-colligative functions.     

Climate change alters elevational phenology patterns of the European spruce bark beetle (Ips typographus)

The European spruce bark beetle Ips typographus is the most important insect pest in Central European forests. Under climate change, its phenology is presumed to be changing and mass infestations becoming more likely. While several studies have investigated climate effects across a latitudinal gradient, it remains an open question how phenology will change depending on elevation and topology. Knowing how an altered climate is likely to affect bark beetle populations, particularly across diverse topographies and elevations, is essential for adaptive management. We developed a time‐varying distributed delay model to predict the phenology of I. typographus. This approach has the particular advantage of capturing the variability within populations and thus representing its stage structure at any time. The model is applied for three regional climate change scenarios, A1B, A2 and RCP3PD, to the diverse topography of Switzerland, covering a large range of elevations, aspects and slopes. We found a strong negative relationship between voltinism and elevation. Under climate change, the model predicts an increasing number of generations over the whole elevational gradient, which will be more pronounced at low elevations. In contrast, the pre‐shift in spring swarming is expected to be greater at higher elevations. In comparison, the general trend of faster beetle development on steep southern slopes is only of minor importance. Overall, the maximum elevation allowing a complete yearly generation will move upwards. Generally, the predicted increase in number of generations, earlier spring swarming, more aggregated swarming, together with a projected increase in drought and storm events, will result in a higher risk of mass infestations. This will increase the pressure on spruce stands particularly in the lowlands and require intensified management efforts. It calls for adapted long‐term silvicultural strategies to mitigate the loss of ecosystem services such as timber production protection against rockfall and avalanches and carbon storage.     

Behavioural sequence in the attraction of the bark beetle Ips typographus to pheromone sources

ABSTRACT. The functions of the two synergistic pheromone components, (4S)- cis -verbenol (cV) and 2-methyl-3-buten-2-01 (MB), and the role of ipsdienol in the attraction of Ips typographus (L.) (Scolytidae) to pheromone sources were studied in the field. Absolute and relative beetle catches were compared between several traps placed at and nearby a central pheromone source: a pipe trap containing the source, a surrounding sticky trap, a nearby window trap, and four distant window traps. A higher catch in the outer down-wind distant traps indicated an up-wind anemotaxis to the source. Increased MB release, with cV constant, increased the proportion caught in the central pipe trap, indicating MB as a landing stimulus. Release of MB alone gave a very small catch. Ipsdienol could not substitute for cV in the synergism with MB. An increase of cV, with MB constant, increased the number of beetles caught, but not the proportion caught in the pipe trap. The sex ratio was equal in the window traps, but fell to 30% males in both sticky and pipe traps, showing that a large proportion of the males attracted to the source did not land. The proportion of males in the pipe trap was reduced at the highest cV dose. The results support the idea of each pheromone component having a different relative importance in releasing different steps in the behavioural chain.     

Reproductive correlates of mating system variation in Eichhornia paniculata (Spreng.) Solms (Pontederiaceae)

Comparative studies of related plant species indicate that evolutionary shifts in mating systems are accompanied by changes in reproductive attributes such as flower size, floral morphology, and pollen/ovule ratio. Recent theoretical work suggests that patterns of investment in reproduction should also change with the mating system. In a glasshouse study, we investigated the extent to which mating system differences among populations of Eichhornia paniculata (Pontederiaceae) were correlated with changes in allocation to male and female function, floral display, and the regulation of investment in reproduction through fruit and ovule abortion. Significant differences in the amount of biomass allocated to reproductive structures were evident among six populations of E. paniculata. As predicted by sex allocation theory, the proportion of dry weight allocated to male function decreased with the outcrossing rate of populations. Six of the eight attributes used to characterize floral display also differed significantly among populations. However, with the exception of two attributes describing the number of flowers produced by inflorescences, these were not correlated with outcrossing rate. Levels of fruit and ovule abortion were determined in two populations with contrasting mating systems under different nutrient and pollination treatments. Virtually all fruits initiated by plants from a self-fertilizing population were matured, while the amount of fruit abortion in an outcrossing population increased with flower production. Ovule abortion was low in both populations. Our results demonstrate that the evolution of self-fertilization in E. paniculata is associated with changes in investment to reproduction that normally distinguish selfing and outcrossing species.     

Behavior of male and female spruce bark beetles,Ips typographus,on the bark of host trees during mass attack

The behavior of 118 spruce bark beetles, Ips typographus,was observed on trees under colonization. Most individuals were followed from when they landed until they entered or left the tree. Both males and females spent most time inspecting crevices and searching for a place to start boring or for a hole to enter. These behaviors accounted for 87 and 70% of all behavioral acts recorded for males and females, respectively. Females entered galleries with males only after a period of pushing at the gallery entrance. Males spent on average 3 min and females 4 min on the bark before entering or leaving the tree. Thirty-three percent of the beetles eventually entered the tree, 31% flew away, 35% dropped from the host, and one beetle was eaten by a predator. The results are discussed in relation to the question of mate choice in bark beetles and to studies on attack dynamics of spruce bark beetle populations.     

Range expansion of the small spruce bark beetle Ips amitinus: a newcomer in northern Europe

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Effect of male and female age on the mating success of the obliquebanded leafrollerChoristoneura rosaceana (Lepidoptera: Tortricidae) under different ecological conditions

The present study was undertaken to test the hypothesis that male and female age, as well as temperature, can affect the mating success ofChoristoneura rosaceana, given the role that these two factors play in the pheromone biology of this species. In the laboratory, the mating success of females generally declined linearly with age, whereas in males, it increased during the first 3 days and then decreased. The decline in female mating success was more pronounced under warm than cool thermocycles, while the changes observed in males were greater under fluctuating than constant temperature regimes. The onset time of mating was unaffected by male age, however, older females always mated earlier than younger ones, with the advance being more pronounced at cool than warm temperatures. Similar results were also obtained under field conditions. When a single 3-day-old male was provided with 0-, 3-, and 5-day-old females simultaneously, older females obtained mates significantly more often than younger individuals at all temperatures, indicating that calling earlier may afford a reproductive advantage to older females. At both constant temperatures, the time spent mating was longer in older than in younger females, but not under fluctuating thermocycles. Very young and very old males generally spent more time in copula than middle-aged individuals both at constant temperatures and under the warm thermocycle. Under the cool thermocycle, the duration of mating was considerably prolonged at all ages, which could increase the risk of predation.     

Variation in floral longevity in the genus Leptosiphon: mating system consequences

Pollination or fertilisation trigger floral senescence in a wide range of flowering plants, and yet little attention has been given to the implications of this phenomenon to mating system evolution. We examined the effects of pollination on floral senescence in the genus Leptosiphon. Species in the genus exhibit a wide range of breeding systems. In all cases, compatible pollination induced senescence; emasculated flowers lived longer than hand‐outcrossed flowers. In the self‐compatible species, Leptosiphon acicularis and L. bicolor, and in one highly selfing population of L. jepsonii, unmanipulated flowers had reduced longevity compared to emasculated flowers, suggesting that autonomous self‐pollination limits floral longevity in these species. Limited floral longevity in these highly selfing taxa may reduce opportunities for male outcross success, representing a possible source of selection on the mating system. In turn, the mating system might influence how selection acts on floral longevity; obligately outcrossing taxa are expected to benefit from longer floral longevities to maximise opportunities for pollination, while selfing taxa might benefit from earlier floral senescence to reduce resource expenditure. Overall, the longevity of unpollinated flowers increased with the level of outcrossing in the genus Leptosiphon. Our results taken together with those of a previous study and similar results in other species suggest that floral longevity may represent a largely unexamined role in mating system evolution.     

Characterization of microsatellite loci in the spruce bark beetle Ips typographus (Coleoptera: Scolytinae)

Ips typographus is an economically important pest of Norway spruce stands. We developed five polymorphic microsatellite markers using a biotin enrichment protocol. The number of alleles ranged from three to 11 per locus and no strong evidence for null alleles was found. Heterozygosity ranged from 0.3 to 0.97. These markers could be useful tools to study the population structure and genetic consequences of I. typographus population outbreaks.