Possible mechanisms of the difference in sensitivity of caterpillars of Adoxophyes orana and Laspeyresia pomonella to diflubenzuron

The sensitivity to diflubenzuron varies considerably among species of caterpillars that cause damage to fruit. The cause of this difference in sensitivity was studied in larvae of Adoxophyes orana F. R., a not so sensitive species and Laspeyresia pomonella L., a species that is highly sensitive. Results indicate that the ingestion pattern of diflubenzuron and significance of chitin synthesis to these species are of importance for explaining the difference. It is uncertain whether there is a difference in the affinity of the sites of action of A. orana and L. pomonella for diflubenzuron.

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Résumé La sensibilité au diflubenzuron varie considérablement suivant les espèces de lépidoptères qui provoquent des dégâts aux fruits. La cause de ces différences de sensibilité a été étudiée chez les larves d'Adoxophyes orana, une espèce peu sensible, et de Laspeyresia pomonella qui est très sensible. Les résultats soulignent l'importance du processus d'ingestion du diflubenzuron et de la synthèse de la chitine pour expliquer cette différence. Il n'est pas sûr qu'il y ait une différence d'affinité au diflubenzuron des cibles de A. orana et L. pomonella.

     

Host locating behaviour of Leschenaultia exul and Patelloa pachypyga: two tachinid parasitoids of the forest tent caterpillar, Malacosoma disstria

Leschenaultia exul (Townsend) and Patelloa pachypyga (Aldrich & Webber) (Diptera: Tachinidae) are the principal larval parasitoids of the forest tent caterpillar (FTC) Malacosoma disstria (Hübner) (Lepidoptera: Lasiocampidae) in Canada. The response of these two fly species to M. disstria differs depending on the tree species on which the host feeds. In wind tunnel experiments, L. exul spent more time on the side of the tunnel containing volatiles from FTC frass and was attracted to the FTC-aspen poplar (Populus tremuloides Michx.) complex preferentially to the FTC-balsam poplar (Populus balsamifera L.) complex. Field bioassays confirmed that this fly species was preferentially attracted to the herbivore-aspen poplar complex as compared to the herbivore-balsam poplar complex. In field bioassays, P. pachypyga was also attracted preferentially to aspen poplar trees containing FTC larvae, compared to balsam poplar trees with host larvae.     

Biochemical ecology of the forest tent caterpillar: responses to dietary protein and phenolic glycosides

Summary Interactions between quaking aspen (Populus tremuloides) and the forest tent caterpillar (Malacosoma disstria) are likely to be influenced by leaf protein and phenolic glycoside levels, and insect detoxication activity. We investigated the direct and interactive effects of dietary protein and phenolic glycosides on larval performance and midgut enzyme activity of forest tent caterpillars. We conducted bioassays with six artificial diets, using both first and fourth stadium larvae. Four of the diets comprised a 2×2 factorial design-two levels of protein, each with and without phenolic glycosides. Additionally, we assayed high protein diets containing S,S,S-tributylphosphorotrithioate (DEF, an esterase inhibitor) and DEF plus phenolic glycosides. Enzyme solutions were prepared from midguts of sixth instars and assayed for -glucosidase, esterase and glutathione transferase activities. First instar mortality and development times were higher for larvae on diets low in protein or containing phenolic glycosides. Effects of phenolic glycosides were especially pronounced at low protein levels and when administered with DEF. Fourth instar development times were prolonged, and growth rates reduced, in response to consumption of low protein diets. Effects of phenolic glycosides on growth were less pronounced, although the effect for larvae on the low protein diet was nearly significant. Activity of each of the enzyme systems was reduced in larvae reared on low protein diets, and esterase activity was induced in larvae fed phenolic glycosides. Our results suggest that larval performance may be strongly affected by levels of protein and phenolic glycosides commonly occurring in aspen foliage, and that these factors may play a role in differential defoliation of aspen by forest tent caterpillars.     

Use of pheromone mimic to cause the disintegration and collapse of colonies of tent caterpillars (Malacosoma spp.)

The disruption of the trail-based communication system of eastern tent caterpillars (ETC) ( Malacosoma americanum ) and forest tent caterpillars (FTC) ( M. disstria ) by spraying host trees with a trail pheromone mimic caused the disintegration and collapse of young colonies. A 1-ppm formulation of 5β-cholestan-3-one or a control formulation was sprayed on trees either before or after eclosion of the caterpillars in the spring. For pre-eclosion trials, an average of 92% of the FTC colonies on control trees, but only 17% of colonies on treated trees consisted of viable, cohesive aggregates when survival was assessed 5–23 days post-spray. The remaining colonies had either completely disappeared or were reduced to small, disintegrated fragments. For the ETC, 100% of colonies on control trees and an average of 12% of colonies on treated trees consisted of cohesive aggregates inhabiting tents when survival was assessed 3–41 days post-spray. The remaining colonies were completely destroyed, reduced to scattered individuals, or to small, disintegrated, shelter-less fragments. For post-eclosion trials with the FTC in which colonies were sprayed during their first or second larval stadium, an average of 63% of individuals in control groups but only 7% in treatment groups were still on the sprayed trees 5–18 days post-spray. For the ETC, colonies were largely unaffected when trees were not sprayed until after the caterpillars had eclosed and established tents. For all trials, the loss of individuals on treated trees was largely attributable to the inability of dispersed and isolated first or second instar caterpillars to maintain secure purchase, causing them to fall from trees and perish. To our knowledge, this is the first study to investigate the potential of manipulating populations of pest species by interfering with a trail-based, chemical communication system.     

Fluctuating asymmetry and survival ability in the forest tent caterpillar mothMalacosoma disstria: implications for pest management

Fluctuating asymmetry of the first tarsal segment of the proleg of the forest tent caterpiller mothMalacosoma disstria Hbn. (Lepidoptera: Lasiocampidae) was significantly inversely related to survival ability in the lab. The monitoring of population levels of fluctuating asymmetry could have important implications in pest management of this and other species by providing an indication of the health of a population.     

Response of the western spruce budworm to temperature and dose of a virus, a growth regulator, and an organophosphate

Pathogenicity of nuclear polyhedrosis virus (NPV) to western spruce budworm larvae, Choristoneura occidentalis Freeman, increased as temperature increased. In constrast, at temperature extremes, mortality increased for a specified dose of malathion or diflubenzuron, while at the optimal temperatures (20–25°C), mortality decreased. Malathion was the fastest acting insecticide, followed by diflubenzuron and then NPV.Simulation results considered temperature dependent developmental rates of the larvae, energy consumption, time to achieve total mortality, and mortality at specified doses of insecticides. Low temperatures provided the greatest reduction in the amount of energy consumed by spruce budworm relative to the energy consumed when no treatment was applied. This was due to both the percent mortality and because total mortality was realized in the larval stage while at the higher temperatures, mortality was not fully realized until the pupal stage.

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Résumé La température modifie la toxicité ou la pathogénie du virus de la polyhédrose nucléaire (NPV), du diflubenzuron, et du malathion consommés par Choristoneura occidentalis Freeman. La pathogénie du NPV augmente avec la température, si bien qu'il y a une relation linéaire entre mortalité et température. Pour le diflubenzuron et le malathion, la température est liée à la mortalité d'une façon gradiatique. Aux températures extrêmes, la mortalité augmente pour une dose donnée de malathion ou de diflubenzuron, tandis qu'aux températures optimales (20 à 25°C), la mortalité diminue. Des modèles multiples ont été utilisés pour évaluer les effets ci-dessus.Le moment de la mortalité finale observée et la mortalité cumulative ont été modifiés par la température, mais non par la dose d'insecticide. L'effet le plus rapide est obtenu avec le malathion, suivi par le diflubenzuron et enfin le NPV.Selon les résultats de simulation,—tenant compte des taux de développement larvaires à différentes températures, de la consommation d'énergie, du temps nécessaire pour obtenir la mortalité totale calculée et de la mortalité calculée, pour une dose donnée d'insecticide à une température particulière —, ce sont les basses températures qui réduisent le plus l'énergie consommée par la population par comparaison avec l'énergie consommée en l'absence de traitement. Ceci est dû au pourcentage de mortalité calculée et au fait que la mortalité est toujours obtenue au stade larvaire, tandis qu'aux températures plus élevées, la mortalité se poursuit jusqu'au stade nymphal.

     

Evidence of a physiological basis for the boreal-deciduous forest ecotone in North America

The observed northern limit of the deciduous forest formation in North America is shown to agree closely with the reported –40°C average annual minimum temperature isotherm. This indicates that supercooling as a means of resisting freezing stresses may set a physiological limit on the northern expansion of the deciduous forest formation.Abbreviation LTE= Low Temperature Exotherm     

Morphological and anatomical factors responsible for varied susceptibility of some species of spruce to infestation by spruce spider mie (Oligonychus ununguis Jacobi)

Differences in susceptibility to infestation by spruce spider mite of 3 investigated spruce species (Picea glauca ‘Conica’, P. pungens and P. omorika) may be due to features of anatomical and morphological structure of needles. In P. omorika, showing some resistance to the spruce spider mite, we noted lamellar structure of epidermal cell walls and extensive supporting tissues (hypodermis and sclerenchyma fibres) at the whole circumference of the needle.     

Ecosystem function for water retention and forest ecosystem conservation in a watershed of the Yangtze River

The ecosystem function for water retention in a watershed of the Yangtze River was discussed in this study. The watershed was divided into 90 types of vegetation–soil–slope complex. A GIS-embodied spatial database was used to explore the relationships between the capacity of water retention by a complex and its types of vegetation, soil and slope. Furthermore, the capacity of water retention of every complex was estimated statistically by using estimation models. The spatial distribution of various capacity of water retention in the watershed was demarcated on a map based on the attributions and the locations of complexes. In addition, we evaluated integrally the situation of water retention in the watershed based on the estimation for the complexes from which it was distinctly recognized that the serious situation mainly results from the poor capacity of water retention of vegetation. The variation-location effect describes the phenomenon in which an identical variation of a factor may produce different effects on overall situation, when this variation occurs in a different spatial location. According to the variation-location effect on the expansion of forestland, a strategy 'spatial pattern-based forestland extension was proposed to conserve forest ecosystem and improve the situation of water retention in the watershed.     

An eddy covariance mesonet to measure the effect of forest age on land–atmosphere exchange

We deployed a mesonet of year‐round eddy covariance towers in boreal forest stands that last burned in ～1850, ～1930, 1964, 1981, 1989, 1998, and 2003 to understand how CO₂ exchange and evapotranspiration change during secondary succession. We used MODIS imagery to establish that the tower sites were representative of the patterns of secondary succession in the region, and Landsat images to show that the individual stands have changed over the last 22 years in ways that match the spatially derived trends. The eddy covariance towers were well matched, with similar equipment and programs, which maximized site‐to‐site precision and allowed us to operate the network in an efficient manner. The six oldest sites were fully operational for ～90% of the growing season and ～70% of the dormant season from 2001 or 2002 to 2004, with most of the missing data caused by low battery charge or bad signals from the sonic anemometers. The rates of midday growing‐season CO₂ uptake recovered to preburn levels within 4 years of fire. The seasonality of land–atmosphere exchange and growing‐season length changed markedly with stand age. The foliage in the younger stands (1989, 1998, and 2003 burns) was almost entirely deciduous, which resulted in comparatively short growing seasons that lasted ～65 days. In contrast, the older stands (1850, 1930, 1964, and 1981) were mostly evergreen, which resulted in comparatively long growing seasons that lasted ～130 days. The eddy covariance mesonet approach we describe could be used within the context of other ecological experimental designs such as controlled manipulations and gradient comparisons.     

The effect of harvesting intensity on the fate of applied 15N-ammonium to the organic horizons of a coniferous forest in N. Wales

¹⁵N-ammonium sulphate equivalent to 0.5 kg N/ha was added as a tracer to lysimeters containing the organic horizons of an acid forest soil. The effect of logging debris (brash), vegetation and second rotationPicea sitchensis seedlings on the amount of the¹⁵N found in various soil, vegetation and leachate pools was followed over a period of 60 days. Transformation of¹⁵N-ammonium to nitrate occurred within 24 hours. Although total nitrate leachate losses were high, tracer-derived nitrate represented only 0.4%–4.2% of the applied¹⁵N-ammonium. The atom % excess of the KCI-extractable organic-N pool was initially lower than for the inorganic species but due to the large pool size, consistently represented 3–6% of the applied¹⁵N-ammonium. The similarity of the atom % excess of the ammonium and nitrate pools indicated an autotrophic nitrification pathway.A significant proportion of the¹⁵N-ammonium passed through the microbial biomass which contained between 16 and 48% of the¹⁵N-ammonium 2 days after addition of the¹⁵N-ammonium. This nitrogen was in a readily available form or short-term pool for the first two weeks (with no change in the overall biomass pool), after which the nitrogen appeared to become transformed into more stable compounds representing a long-term pool. Total recovery of the¹⁵N was between 68% and 99% for the different treatments. The presence of brash reduced microbial immobilisation of the¹⁵N-ammonium and total retention in the organic matter. This is suggested to be a consequence of greater nitrification and denitrificatiion rate in organic horizons beneath a brash covering due to different microclimatic conditions.     

Statistical analysis for the spatial validity of a model to forecast the daily number of forest fires

In earlier papers a qualitative and quantitative model was developed for predicting the number of forest fires occurring per day. This model permits the forecast at 00.00 hours Universal Time Convention (UTC) of any day (d), the number of forest fires per day for a range of several days (d tod+5) over a particular region. Input data are the number of forest fires in the region during two preceding days (d–2 andd–1) and the type of day (real and evaluated from radiosonde ford–2,d–1,d and predicted from meteorological medium-range forecasts, i.e. of European Centre, ford+1,d+2,d+3,d+4 andd+5. As this model requires data obtained by radiosonde, particularly temperatures and geopotentials at 850 and 700 hPa and dew points (or specific humidity) at 850 hPa, this study investigates the spatial validity of the model in relation to the distance from the radiosonde station (RS). The highest quality forecast is obtained for the region immediately surrounding the RS, and diminishes with increasing distance from it, this being due to the data obtained from the RS not being representative of the atmospheric column over the region. Hence, the derivation of the critical distance for a particular quality level of measurement. Conversely, fixed quality level implies a specific separation between RS and the region for the prediction, with a higher predictive quality implying a shorter distance.     

Pushed to the limit: consequences of climate change for the Araucariaceae: a relictual rain forest family

Background and Aims

Under predicted climate change scenarios, increased temperatures are likely to predispose trees to leaf and other tissue damage, resulting in plant death and contraction of already narrow distribution ranges in many relictual species. The effects of predicted upward temperatures may be further exacerbated by changes in rainfall patterns and damage caused by frosts on trees that have been insufficiently cold-hardened. The Araucariaceae is a relictual family and the seven species found in Australia have limited natural distributions characterized by low frost intensity and frequency, and warm summer temperatures. The temperature limits for these species were determined in order to help understand how such species will fare in a changing climate.

Methods

Experiments were conducted using samples from representative trees of the Araucariaceae species occurring in Australia, Agathis (A. atropurpurea, A. microstachya and A. robusta), Arauacaria (A. bidwilli, A. cunninghamii and A. heterophylla) and Wollemia nobilis. Samples were collected from plants grown in a common garden environment. Lower and higher temperature limits were determined by subjecting detached winter-hardened leaves to temperatures from 0 to –17 °C and summer-exposed leaves to 25 to 63 °C, then measuring the efficiency of photosystem II (F_v/F_m) and visually rating leaf damage. The exotherm, a sharp rise in temperature indicating the point of ice nucleation within the cells of the leaf, was measured on detached leaves of winter-hardened and summer temperature-exposed leaves.

Key Results

Lower temperature limits (indicated by FT₅₀, the temperature at which PSII efficiency is 50 %, and LT₅₀ the temperature at which 50 % visual leaf damage occurred) were approx. –5·5 to –7·5 °C for A. atropurpurea, A. microstachya and A. heterophylla, approx. –7 to –9 °C for A. robusta, A. bidwillii and A. cunninghamii, and –10·5 to –11 °C for W. nobilis. High temperature damage began at 47·5 °C for W. nobilis, and occurred in the range 48·5–52 °C for A. bidwillii and A. cunninghamii, and in the range 50·5–53·5 °C for A. robusta, A. microstachya and A. heterophylla. Winter-hardened leaves had ice nucleation temperatures of –5·5 °C or lower, with W. nobilis the lowest at –6·8 °C. All species had significantly higher ice nucleation temperatures in summer, with A. atropurpurea and A. heterophylla forming ice in the leaf at temperatures >3 °C higher in summer than in winter. Wollemia nobilis had lower FT₅₀ and LT₅₀ values than its ice nucleation temperature, indicating that the species has a degree of ice tolerance.

Conclusions

While lower temperature limits in the Australian Araucariaceae are generally unlikely to affect their survival in wild populations during normal winters, unseasonal frosts may have devastating effects on tree survival. Extreme high temperatures are not common in the areas of natural occurrence, but upward temperature shifts, in combination with localized radiant heating, may increase the heat experienced within a canopy by at least 10 °C and impact on tree survival, and may contribute to range contraction. Heat stress may explain why many landscape plantings of W. nobilis have failed in hotter areas of Australia.     

A formula for the mean infection success per miracidium and a method of proving the homogeneous susceptibility of snail populations to trematode infection

A formula for computing the mean infection success per miracidium (“infection index”) is given for every permutation of the numbers of snails and miracidia in miracidial exposure experiments. This “infection index” allows the comparison of the results from quantitatively different exposure methods and may be important for characterizing special trematode- intermediate host systems. By means of the “infection index” it is shown that a laboratory population of Lymnaea stagnalis is homogeneous with regard to its susceptibility to Isthmiophora melis miracidia, i.e. that there is no appreciable rate of resistant individuals. Some experimental results which have been published by other authors and have been interpreted by them as indicating the resistance of a portion of snail populations can be numerically explained by means of the formula of the “infection index” and without necessarily assuming resistance.     

A 12 000-rad whole-genome radiation hybrid panel in sheep: application to the study of the ovine chromosome 18 region containing a QTL for scrapie susceptibility

Whole-genome radiation hybrid (RH) panels have been constructed for several species, including cattle. RH panels have proven to be an extremely powerful tool to construct high-density maps, which is an essential step in the identification of genes controlling important traits, and they can be used to establish high-resolution comparative maps. Although bovine RH panels can be used with ovine markers to construct sheep RH maps based on bovine genome organization, only some (c. 50%) of the markers available in sheep can be successfully mapped in the bovine genome. So, with the development of genomics and genome sequencing projects, there is a need for a high-resolution RH panel in sheep to map ovine markers. Consequently, we have constructed a 12 000-rad ovine whole-genome RH panel. Two hundred and eight hybrid clones were produced, of which 90 were selected based on their retention frequency. The final panel had an average marker retention frequency of 31.8%. The resolution of this 12 000-rad panel (SheepRH) was estimated by constructing an RH framework map for a 23-Mb region of sheep chromosome 18 (OAR18) that contains a QTL for scrapie susceptibility.     

Contribution of terrestrial invertebrates to the annual resource budget for salmonids in forest and grassland reaches of a headwater stream

1. The annual input, contribution to the diet of salmonids, and quantitative input of terrestrial invertebrates to four reaches with contrasting forest (n=2) and grassland riparian vegetation (n=2) were compared in a Japanese headwater stream.
2. The annual input of terrestrial invertebrates falling into the forest reaches (mean±1 SE=8.7×10³±0.3×10³ mg m^?2 year^?1) was 1.7 times greater than that in the grassland reaches (5.1×10³±0.8×10³ mg m^?2 year^?1), with clear seasonality in the daily input of invertebrates in both vegetation types. The daily input, however, differed between the vegetation types only in summer, when it rose to a maximum in both vegetation types.
3. Fish biomass also differed among the seasons in both vegetation types, being less in the grassland reaches. The contribution of terrestrial invertebrates to the salmonid diet in the forest and grassland reaches was 11 and 7% in spring, 68 and 77% in summer, 48 and 33% in autumn, and 1 and 1% in winter, respectively. The prey consumption rate of fish, which was similar between the vegetation types, increased with stream temperature and was highest in summer. Terrestrial invertebrates supported 49% (mean±1 SE=5.3×10³±0.4×10³ mg m^?2 year^?1) of the annual, total prey consumption (10.9×10³±1.7×10³ mg m^?2 year^?1) by salmonids in the forest and 53% (2.0×10³±0.3×10³ mg m^?2 year^?1) (3.8×10³±0.6×10³ mg m^?2 year^?1) in the grassland reaches.
4. Salmonids were estimated to consume 51 and 35% of the annual total (falling plus drift) input of terrestrial invertebrates in the forest and grassland reaches, respectively. The input of terrestrial invertebrates by drift, however, was almost equal to the output in both vegetation types, suggesting that the reach‐based, in‐stream retention of terrestrial invertebrates almost balanced these falling in.
5. Difference in the riparian vegetation, which caused spatial heterogeneity in the input of terrestrial invertebrates, could play an important role in determining the local distribution of salmonids.     

Phosphoinositide 3-kinase/Akt signalling is responsible for the differential susceptibility of myoblasts and myotubes to menadione-induced oxidative stress

In this study, it was found that undifferentiated myoblasts were more vulnerable to menadione-induced oxidative stress than differentiated myotubes. Cell death occurred with a relatively low concentration of menadione in myoblasts compared to myotubes. With the same concentration of menadione, the Bcl-2/Bax ratio decreased and nuclei containing condensed chromatin were observed in myoblasts to a greater extent than in myotubes. However, myotubes became increasingly susceptible to menadione when phosphoinositide 3-kinase (PI3-K) was blocked by pre-incubation with LY294002, a PI3-K inhibitor. Actually, PI3-K activity was reduced by menadione in myoblasts but not in myotubes. In addition, the phosphorylation of Akt, a downstream effector of PI3-K, was inhibited in myoblasts by menadione but increased in myotubes. Both LY294002 and API-2, an Akt inhibitor, decreased the Bcl-2/Bax ratio in menadione-exposed myotubes. These results suggest that the differential activity of PI3-K/Akt signalling is responsible for the differential susceptibility of myoblasts and myotubes to menadione-induced oxidative stress.     

A comparison of sites suitable for the seedling establishment of two co-occurring species, Swintonia glauca and Stemonurus scorpioides, in a tropical peat swamp forest

Spatial and temporal ground-surface dynamics are major factors that affect regeneration and species coexistence in tropical peat swamp forests. We studied the seedling survivorship and morphological features of two tree species that play important roles in maintaining the ground-surface dynamics of a peat swamp forest in Sumatra. Large Swintonia glauca trees form mounds, whereas large Stemonurus scorpioides trees occupy non-mounds. We monitored the demography of naturally dispersed Swintonia and Stemonurus seedlings that germinated in 2000. Survivorship of Swintonia seedlings was high under conditions of late germination, high-light environment, and elevated ground surface, and was negatively affected by distance to the nearest conspecific adult. Survivorship of Stemonurus was high under conditions of early germination and high conspecific seedling density, and was also negatively affected by distance to the nearest conspecific adult. The allometric features of Stemonurus seedlings indicated characteristics of stress tolerance, that is, low growth rate and thick, porous roots. Stemonurus, which has large wingless seeds, regenerated in non-mounds around the parental trees, while winged Swintonia seeds dispersed farther from the parent and established in patchily distributed gaps and mounds. Thus, Swintonia seedlings can survive on non-mound sites within gaps and possibly create mounds, while Stemonurus seedlings tend to maintain non-mounds around the parental trees.