Soluble and filamentous proteins in Arabidopsis sieve elements

Phloem sieve elements are highly differentiated cells involved in the long-distance transport of photoassimilates. These cells contain both aggregated phloem-proteins (P-proteins) and soluble proteins, which are also translocated by mass flow. We used liquid chromatography-tandem mass spectrometry (LC-MS/MS) to carry out a proteomic survey of the phloem exudate of Arabidopsis thaliana, collected by the ethylenediaminetetraacetic acid (EDTA)-facilitated method. We identified 287 proteins, a large proportion of which were enzymes involved in the metabolic precursor generation and amino acid synthesis, suggesting that sieve tubes display high levels of metabolic activity. RNA-binding proteins, defence proteins and lectins were also found. No putative P-proteins were detected in the EDTA-exudate fraction, indicating a lack of long-distance translocation of such proteins in Arabidopsis. In parallel, we investigated the organization of P-proteins, by high-resolution transmission electron microscopy, and the localization of the phloem lectin PP2, a putative P-protein component, by immunolocalization with antibodies against PP2-A1. Transmission electron microscopy observations of P-proteins revealed bundles of filaments resembling strings of beads. PP2-A1 was found weakly associated with these structures in the sieve elements and bound to plastids. These observations suggest that PP2-A1 is anchored to P-proteins and organelles rather than being a structural component of P-proteins.     

Role of intraguild predation in aphidophagous guilds

The concept of intraguild predation (IGP) appeared in 1987–1989 to describe trophic interactions within a guild of arthropods inhabiting a sand dune desert: consumers B prey on consumers A and both of them prey on a common resource. Theory predicts that the two types of consumers should only coexist if consumer A is more efficient in the conversion of the common resource than B. As a consequence, this resource is more abundant in the presence than in the absence of intraguild predators. Such a theoretical prediction probably explains the vivid interest shown by ecologists involved in biological control for IGP. It is therefore not surprising that many papers report on IGP among natural enemies of aphids. A close examination of these reported cases indicates that they rarely fulfil the theoretical requirements for IGP. That is, guilds of aphidophagous insects are rarely the theatre of IGP but frequently of interspecific predation. This is confirmed by experimental assessment of the cost of attacking and eating intraguild prey instead of extraguild in ladybird beetles.     

The effects of habitat,density, gender and duration on overwintering success in Bembidion lampros (Coleoptera: Carabidae)

In temperate climates, winter mortality is a key factor influencing insect survival. In Bembidion lampros (Coleoptera: Carabidae), an abundant polyphagous predator in arable farmland, we investigated how habitat, population density, gender and duration of overwintering affect the winter mortality and body condition of survivors. In a field experiment, we introduced beetles at two population densities into isolators placed either in the interior of the field or in the grassy boundary. Half of the isolators were collected in mid‐March, and the remaining half were collected in mid‐April. Across all treatments, 44–92% of the beetles survived until spring. Survival was significantly higher in the field interior than in the boundary. The longevity of individuals starved after overwintering was higher in females than in males and was positively related to the length of time spent at the overwintering site. Population density was positively related to percentage survival but did not affect body condition. Our results suggest that biotic factors such as population density and predation, though little studied, may have a similar significance as abiotic factors. Even ubiquitous carabid species inhabiting agroecosystems have specific requirements for overwintering. Understanding these requirements is useful for developing techniques to support their overwintering success.     

Radiative forcing of natural forest disturbances

Forest disturbances are major sources of carbon dioxide to the atmosphere, and therefore impact global climate. Biogeophysical attributes, such as surface albedo (reflectivity), further control the climate‐regulating properties of forests. Using both tower‐based and remotely sensed data sets, we show that natural disturbances from wildfire, beetle outbreaks, and hurricane wind throw can significantly alter surface albedo, and the associated radiative forcing either offsets or enhances the CO₂ forcing caused by reducing ecosystem carbon sequestration over multiple years. In the examined cases, the radiative forcing from albedo change is on the same order of magnitude as the CO₂ forcing. The net radiative forcing resulting from these two factors leads to a local heating effect in a hurricane‐damaged mangrove forest in the subtropics, and a cooling effect following wildfire and mountain pine beetle attack in boreal forests with winter snow. Although natural forest disturbances currently represent less than half of gross forest cover loss, that area will probably increase in the future under climate change, making it imperative to represent these processes accurately in global climate models.     

Area‐wide application of verbenone‐releasing flakes reduces mortality of whitebark pine Pinus albicaulis caused by the mountain pine beetle Dendroctonus ponderosae

• 1 DISRUPT Micro‐Flake Verbenone Bark Beetle Anti‐Aggregant flakes (Hercon Environmental, Inc., Emigsville, Pennsylvania) were applied in two large‐scale tests to assess their efficacy for protecting whitebark pine Pinus albicaulis Engelm. from attack by mountain pine beetle Dendroctonus ponderosae Hopkins (Coleoptera: Scolytinae) (MPB). At two locations, five plots of equivalent size and stand structure served as untreated controls. All plots had early‐ to mid‐outbreak beetle populations (i.e. 7.1–29.2 attacked trees/ha). Verbenone was applied at 370 g/ha in both studies. Intercept traps baited with MPB aggregation pheromone were placed near the corners of each plot after the treatment in order to monitor beetle flight within the plots. Trap catches were collected at 7‐ to 14‐day intervals, and assessments were made at the end of the season of stand structure, stand composition and MPB attack rate for the current and previous years.
• 2 Applications of verbenone flakes significantly reduced the numbers of beetles trapped in treated plots compared with controls at both sites by approximately 50% at the first collection date.
• 3 The applications also significantly reduced the proportion of trees attacked in both Wyoming and Washington using the proportion of trees attacked the previous year as a covariate in the model for analysis of current year attack rates; in both sites, the reduction was ≥ 50%.
• 4 The flake formulation of verbenone appears to have promise for area‐wide treatment by aerial application when aiming to control the mountain pine beetle in whitebark pine forests.

     

Population dynamics in changing environments: the case of an eruptive forest pest species

In recent decades we have seen rapid and co‐occurring changes in landscape structure, species distributions and even climate as consequences of human activity. Such changes affect the dynamics of the interaction between major forest pest species, such as bark beetles (Coleoptera: Curculionidae, Scolytinae), and their host trees. Normally breeding mostly in broken or severely stressed spruce; at high population densities some bark beetle species can colonise and kill healthy trees on scales ranging from single trees in a stand to multi‐annual landscape‐wide outbreaks. In Eurasia, the largest outbreaks are caused by the spruce bark beetle, Ips typographus (Linnaeus), which is common and shares a wide distribution with its main host, Norway spruce (Picea abies Karst.). A large literature is now available, from which this review aims to synthesize research relevant for the population dynamics of I. typographus and co‐occurring species under changing conditions. We find that spruce bark beetle population dynamics tend to be metastable, but that mixed‐species and age‐heterogeneous forests with good site‐matching tend to be less susceptible to large‐scale outbreaks. While large accumulations of logs should be removed and/or debarked before the next swarming period, intensive removal of all coarse dead wood may be counterproductive, as it reduces the diversity of predators that in some areas may play a role in keeping I. typographus populations below the outbreak threshold, and sanitary logging frequently causes edge effects and root damage, reducing the resistance of remaining trees. It is very hard to predict the outcome of interspecific interactions due to invading beetle species or I. typographus establishing outside its current range, as they can be of varying sign and strength and may fluctuate depending on environmental factors and population phase. Most research indicates that beetle outbreaks will increase in frequency and magnitude as temperature, wind speed and precipitation variability increases, and that mitigating forestry practices should be adopted as soon as possible considering the time lags involved.     

太行山南麓低山丘陵区栓皮栎直径变化及其与环境因子的关系

使用周长传感器(Circumference DC2)研究了太行山南麓低山丘陵上栓皮栎人工林树干直径的日变化及其影响因子.结果表明:在季节性干旱期间,栓皮栎树干的直径变化周期性明显,直径收缩与液流启动时间基本一致,直径最小值滞后于液流速率最大值3 ～4 h;栓皮栎直径日最大收缩量(MDS)呈现低-高-低的变化趋势,与累积液流通量和叶片水势日差值极显著相关,与土壤含水量呈显著的二次方程关系.MDS值受气象因子变化的影响,与温度日差值、蒸汽压亏缺日差值和相对湿度日差值显著相关,而与太阳辐射日差值的相关性不显著.连续降水后,土壤水分不再是栓皮栎直径变化的限制因子,MDS值与累积液流通量、叶片水势、土壤含水量和气象因子差值的相关性均不显著.季节性干旱期和雨季的土壤含水量和温度是影响树干直径日变化的主要因子.     

Stem respiration and carbon dioxide efflux of young <Emphasis Type="Italic">Populus deltoides</Emphasis> trees in relation to temperature and xylem carbon dioxide concentration

Oxidative respiration is strongly temperature driven. However, in woody stems, efflux of CO₂ to the atmosphere (E _A), commonly used to estimate the rate of respiration (R _S), and stem temperature (T _st) have often been poorly correlated, which we hypothesized was due to transport of respired CO₂ in xylem sap, especially under high rates of sap flow (f _s). To test this, we measured E _A, T _st, f _s and xylem sap CO₂ concentrations ([CO₂*]) in 3-year-old Populus deltoides trees under different weather conditions (sunny and rainy days) in autumn. We also calculated R _S by mass balance as the sum of both outward and internal CO₂ fluxes and hypothesized that R _S would correlate better with T _st than E _A. We found that E _A sometimes correlated well with T _st, but not on sunny mornings and afternoons or on rainy days. When the temperature effect on E _A was accounted for, a clear positive relationship between E _A and xylem [CO₂*] was found. [CO₂*] varied diurnally and increased substantially at night and during periods of rain. Changes in [CO₂*] were related to changes in f _s but not T _st. We conclude that changes in both respiration and internal CO₂ transport altered E _A. The dominant component flux of R _S was E _A. However, on a 24-h basis, the internal transport flux represented 9–18% and 3–7% of R _S on sunny and rainy days, respectively, indicating that the contribution of stem respiration to forest C balance may be larger than previously estimated based on E _A measurements. Unexpectedly, the relationship between R _S and T _st was sometimes weak in two of the three trees. We conclude that in addition to temperature, other factors such as water deficits or substrate availability exert control on the rate of stem respiration so that simple temperature functions are not sufficient to predict stem respiration.     

Ultrastructure of the antennal sensorial appendage of larvae of Ophonus ardosiacus (Lutshnik, 1922) (Coleoptera, Carabidae) and possible correlations between size and shape and the larval feeding habits

The antennal sensory appendage morphology was studied in 19 species of carabid beetle larvae using scanning electron microscopy. Shape and size of the organ has been re-examined in selected taxa and are compared to figure out possible correlations between antennal sensory structures and larval morphoecological types. Morphometric analysis shows no correlation between antennal sensory appendage dimension and the four most common behavioural types. The ultrastructure of this sensory organ is described for larvae of Ophonus ardosiacus and the possible function is discussed. Olfactory function has been indicated as the most probable. The high number of chemosensory neurons of this multiporous organ suggests a possible ability of fine odour discrimination related to prey choice or host location.