Walker

Distribution by Scientific Domains
Distribution within Life Sciences

Terms modified by Walker

  • walker a motif

  • Selected Abstracts


    Mixed Effects Models and Extensions in Ecology with R by ZUUR, A. F., IENO, E. N., WALKER, N. J., SAVELIEV, A. A., and SMITH, G. M.

    BIOMETRICS, Issue 3 2009
    Carl James Schwarz
    No abstract is available for this article. [source]


    Walker tumor cells express larger amounts of the antiapoptotic protein Bcl-2 and presents higher resistance to toxic concentrations of Ca2+ than the tumor cells K 562

    DRUG DEVELOPMENT RESEARCH, Issue 4 2001
    Graziela Milani
    Abstract Ca2+ homeostasis was studied in two tumor cell lines (Walker 256 and K 562) previously shown to exhibit different mitochondrial Ca2+ accumulation capacity. When intact, both cells present cytosolic Ca2+ concentrations within the range expected for mammalian cells, as determined through fura-2 fluorescence ratios. In order to study intracellular Ca2+ distribution, digitonin was used to permeabilize the plasma membrane without affecting intracellular organelle structure, as assessed using electron microscopy. Digitonin-permeabilized Walker 256 cells incubated with Ca2+ presented uptake of the cation exclusively through mitochondrial activity. In addition, very large Ca2+ loads were necessary to promote a disruption of Walker 256 mitochondrial membrane potential. K 562 cells presented active Ca2+ uptake through both nonmitochondrial and mitochondrial compartments and suffered disruption of mitochondrial membrane potential at lower Ca2+ loads than Walker 256 mitochondria. The higher Ca2+ resistance in Walker 256 cells could be attributed to Bcl-2 overexpression, as evidenced by immunocytochemical staining. Thus, we correlate natural Bcl-2 overexpression, observed in Walker 256 cells, with higher resistance to mitochondrial Ca2+ overload, as was shown previously in mitochondria from cells transfected with the bcl-2 gene. Drug Dev. Res. 52:508,514, 2001. © 2001 Wiley-Liss, Inc. [source]


    Resilience thinking: Interview with Brian Walker

    ECOLOGICAL MANAGEMENT & RESTORATION, Issue 2 2007
    Tein McDonald
    Summary This interview with Brian Walker, chair of the research-based Resilience Alliance, outlines the main concepts and propositions behind ,resilience thinking' and touches on the importance of this paradigm for individuals and organizations involved in managing complex social-ecological systems. It refers to the origins, work and publications of the Resilience Alliance, listing and elaborating the key case studies used to illustrate the Alliance's main proposition that complex social-ecological systems do not behave in a predictable linear fashion. Rather, research indicates it is normal for complex systems to go through cycles of increasing and decreasing resilience and to have potential to shift, (in a self-organising way) to potentially undesirable states or entirely new systems if certain component variables are severely impacted by management. Such shifts can be novel and ,surprising', and are often not beneficial or desirable for societies. This is particularly the case where small-scale solutions push the problem upwards in a system, causing loss of resilience at a global scale. Predicting thresholds is therefore important to managers and is a key research focus for members of the Resilience Alliance who are currently building an accessible database to support decision-making in global natural resource management. [source]


    Indigestibility of plant cell wall by the Australian plague locust, Chortoicetes terminifera

    ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 3 2004
    F.J. Clissold
    Abstract The plant cell wall may play an important role in defence against herbivores since it can be both a barrier to, and nutrient diluter of, the easily digested cell contents. The aim of this study was to investigate the digestibility of the cell wall of three grasses, Triticum aestivum L., Dactyloctenium radulans (R. Br.) Beauv., and Astrebla lappacea (Lindl.) Domin, by the Australian plague locust, Chortoicetes terminifera Walker (Orthoptera: Acrididae, Acridinae) as determined by the Van Soest method [Van Soest PJ, Robertson JB & Lewis BA (1991) Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. Journal of Dairy Science 74: 3583,3597]. Determination of plant cell wall digestion by locusts required a precise methodological procedure to determine both the exact intake and the concentration of cell wall in the diet and the faeces. Plant cell wall determination is affected by the particle size distribution of the dried plant material. All three grasses differed in the percentage of cell wall per gram dry matter and the proportions of hemicellulose, cellulose, and acid-detergent sulphuric lignin within the cell wall. The locust was unable to digest the cell wall of any of the grasses. Thus, plant cell walls are a mechanical barrier hindering locusts assimilating nutrients. That is, access, rather than nutrient concentration per se, may be limiting nutrient factor. [source]


    Trapping noctuid moths with synthetic floral volatile lures

    ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 3 2002
    Robert L. Meagher Jr.
    Abstract Male and female noctuid moths were collected from plastic bucket traps that were baited with different synthetic floral chemicals and placed in peanut fields. Traps baited with phenylacetaldehyde, benzyl acetate, and a blend of phenylacetaldehyde, benzyl acetate, and benzaldehyde collected more soybean looper moths, Pseudoplusia includens (Walker), than benzaldehyde-baited or unbaited traps. Females comprised over 67% of the moths captured and most were mated. At peak capture, over 90 male and female moths per night were collected. In another experiment, phenylacetaldehyde delivered in plastic stoppers attracted more P. includens moths than traps baited using other substrates, but this chemical delivered in wax attracted more velvetbean caterpillar moths (Anticarsia gemmatalis Hübner). Other noctuid male and female moths collected included Agrotis subterranea (F.), Argyrogramma verruca (F.), Helicoverpa zea (Boddie), and several Spodoptera species. Aculeate Hymenoptera were collected in large numbers, especially in traps baited with phenylacetaldehyde delivered from stoppers. [source]


    Biology of Bactrocera (Zeugodacus) tau (Walker) (Diptera: Tephritidae)

    ENTOMOLOGICAL RESEARCH, Issue 5 2010
    Shakti Kumar SINGH
    Abstract The biology of the fruit fly Bactrocera tau, an important horticultural pest, was studied under laboratory conditions at 25°C and 60,70% relative humidity on Cucurbita maxima. The duration of mating averaged 408.03 ± 235.93 min. After mating, the female fly had a preoviposition period of 11.7 ± 4.49 days. The oviposition rate was 9.9 ± 8.50 eggs and fecundity was 464.6 ± 67.98 eggs/female. Eggs were elliptical, smooth and shiny white, turning darker as hatching approached, and measured 1.30 ± 0.07 mm × 0.24 ± 0.04 mm. The chorion has polygonal microsculpturing and is species-specific with polygonal walls. The egg period lasts for 1.3 ± 0.41 days. The duration of the larval period is 1.2 ± 0.42, 1.7 ± 0.48 and 4.0 ± 0.94 days for first, second and third instars, respectively. Pupation occurs in the sand or soil and pupal periods are 7.0 ± 0.47 days. The life cycle from egg to adult was completed in 14.2 ± 1.69 days; the longevity of mated females and males was 130.33 ± 14.18 and 104.66 ± 31.21 days, respectively. At least two to three generations were observed from June 2008 to June 2009. [source]


    A Taxonomic Revision of Illiberis Walker (Lepidoptera: Zygaenidae: Procridinae) in Korea

    ENTOMOLOGICAL RESEARCH, Issue 4 2004
    Sung-Soo KIM
    ABSTRACT The Korean species of Illiberis Walker are revised. A total of 10 species are recognized, including four species new to Korea: I. rotundata Jordan, I. psychina (OberthÜr), I. consimilis Leech, and I. hyalina (Staudinger). The identities of I. cybele Leech and I. assimilis Jordan, the two ambiguously defined Korean species, are reconfirmed with the examination of type specimens and additional materials. Photos of the adults and type materials are provided, and male and female genitalia of each species are illustrated. Biology and distribution for each species are briefly discussed with the larval host records from Korea. [source]


    Genus Thubana Walker in Indonesia, with descriptions of four new species (Lepidoptera: Lecithoceridae) and a world catalog of the genus

    ENTOMOLOGICAL SCIENCE, Issue 3 2009
    Kyu-Tek PARK
    Abstract The genus Thubana Walker (Lepidoptera: Lecithoceridae: Torodorinae) in Indonesia is reviewed, with three known species from Java and four additional new species: Th. raphidodea sp. nov. from Sulawesi, Indonesia and Malaysia; and Th. erycinae sp. nov., Th. apiculalis sp. nov. and Th. sellarius sp. nov. from Sumatra, Indonesia. The previously known species from Java, Th. costimaculella (Snellen), is redescribed for the wing venation and genitalia of both sexes; however, the syntype of Th. heylaertsi (Snellen) is observed only by its photograph. No specimens of Th. heylaertsi and Th. xylogramma Meyrick were found during this study. Photos of all known species, except Th. xylogramma Meyrick, and a key to species are provided. A catalog for the genus with all 46 known species in the world is given. [source]


    Difference in the time of mating activity between host-associated populations of the rice stem borer, Chilo suppressalis (Walker)

    ENTOMOLOGICAL SCIENCE, Issue 3 2006
    Hideki UENO
    Abstract Mating activities of the rice stem borer, Chilo suppressalis, were compared between rice- and wateroat-feeding populations, and two potential temporal factors that may act as reproductive barriers were examined. Seasonal data of the number of moths attracted to pheromone traps showed that the peak of emergence at the rice field was approximately 10 days earlier than that at the wateroat vegetation in the first flight season, although there was a broad overlap of emergence at the two locations. Both field observations and a laboratory experiment showed that moths from the rice field started mating earlier than those from the wateroat vegetation. However, whereas the difference was distinctive in the laboratory experiment, mating activity at the wateroat vegetation shifted significantly to an earlier time phase than that observed in the laboratory. Body size data showed that the male moths attracted to the pheromone traps at the wateroat vegetation were significantly larger than those at the rice field, suggesting that the traps at the two locations mainly attracted moths originating from different host plants. However, pheromone-trapped males at the rice field were significantly larger than those reared from overwintering samples. These results support the idea that males from the wateroat vegetation migrate to the rice field. The differences in seasonal and temporal mating activity and their effects on development of reproductive isolation between host-associated populations are discussed. [source]


    Effect of the pupal age of Calliphora erythrocephala (Diptera: Calliphoridae) on the reproductive biology of Melittobia acasta (Walker) (Hymenoptera: Chalcidoidea: Eulophidae)

    ENTOMOLOGICAL SCIENCE, Issue 1 2006
    Nyiutaha G. IMANDEH
    Abstract A laboratory experiment was conducted to determine the effect of the pupal age of Calliphora erythrocephala (Meigen) on the reproductive biology (in terms of number, size, developmental time and longevity of progeny) of the parasitoid Melittobia acasta Walker. Melittobia acasta females of uniform size were given five C. erythrocephala pupae from one of four experimental age groups: 17,24 h, 24,48 h, 48,72 h and 72,96 h, for parasitization. The mean number of progeny produced from the experimental age groups for a 24 h period were 2, 7.6, 15.6 and 13.6, respectively. The parasitoids preferred hosts that were 48,72 h old. There were no significant differences in the mean development time (18.2 days) and size of progeny (mean head width = 0.38 ± 0.01 mm) produced from the experimental host age groups. The longevity of progeny from the four host age groups varied (range: 4,39 days), with those from the 48,72 h group living longest (mean = 25 days). The F1 females from the 48,72 h group were reproductively more successful than those from the other groups, producing a mean F2 progeny of 912 individuals when compared with 867, 801 and 757 individuals from the 24,48 h, 72,96 h and 17,24 h age groups, respectively. These findings make significant contributions to our knowledge of the breeding and utilization of this parasitoid for the biological control of dipteran flies in pigsties and poultry houses. [source]


    Effects of hyperventilation on fast goal-directed limb movements in spinocerebellar ataxia type 6

    EUROPEAN JOURNAL OF NEUROLOGY, Issue 5 2001
    M.-U. Manto
    It has been shown previously that hyperventilation modifies the features of the nystagmus in cerebellar patients (Walker and Zee, 1999). It has been hypothesized that hyperventilation influences the oculomotor control through a metabolic effect on cerebellar calcium channels, which play a critical role in the firing behaviour of neuronal populations in the cerebellum. This hypothesis has been tested here by analysing fast goal-directed limb movements before and after hyperventilation in spinocerebellar ataxia type 6 (SCA-6), a disease associated with a polyglutamine expansion in the , 1-A voltage-dependent calcium channel. Cerebellar hypermetria associated with fast distal single-joint movements was found to be increased following hyperventilation in patients presenting SCA-6 but remained unchanged in patients with idiopathic late-onset cerebellar degeneration (ILOCA). This is a new provocative test to enhance distal dysmetria in SCA-6. The present results strengthen the hypothesis of Walker and Zee. It is suggested that hyperventilation enhances the defective calcium transfers in SCA-6, resulting in an impairment of the calcium influx in particular into Purkinje cells involved in the control of fast goal-directed voluntary movements. [source]


    Comparative cytoarchitectonic analysis of the human and the macaque ventrolateral prefrontal cortex and corticocortical connection patterns in the monkey

    EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2002
    M. Petrides
    A comparison of the cytoarchitecture of the human and the macaque monkey ventrolateral prefrontal cortex demonstrated a region in the monkey that exhibits the architectonic characteristic of area 45 in the human brain. This region occupies the dorsal part of the ventrolateral prefrontal convexity just below area 9/46v. Rostroventral to area 45 in the human brain lies a large cortical region labelled as area 47 by Brodmann. The ventrolateral component of this region extending as far as the lateral orbital sulcus has architectonic characteristics similar to those of the ventrolateral prefrontal region labelled by Walker as area 12 in the macaque monkey. We designated this region in both the human and the monkey ventrolateral prefrontal cortex as area 47/12. Thus, area 47/12 designates the specific part of the zone previously labelled as area 47 in the human brain that has the same overall architectonic pattern as that of Walker's area 12 in the macaque monkey brain. The cortical connections of these two areas were examined in the monkey by injecting fluorescent retrograde tracers. Although both area 45 and area 47/12 as defined here had complex multimodal input, they could be differentiated in terms of some of their inputs. Retrograde tracers restricted to area 47/12 resulted in heavy labelling of neurons in the rostral inferotemporal visual association cortex and in temporal limbic areas (i.e. perirhinal and parahippocampal cortex). In contrast, injections of tracers into dorsally adjacent area 45 demonstrated strong labelling in the superior temporal gyrus (i.e. the auditory association cortex) and the multimodal cortex in the upper bank of the superior temporal sulcus. [source]


    The effect of diet on the expression of lipase genes in the midgut of the lightbrown apple moth (Epiphyas postvittana Walker; Tortricidae)

    INSECT MOLECULAR BIOLOGY, Issue 1 2010
    J. T. Christeller
    Abstract We have identified lipase-like genes from an Epiphyas postvittana larval midgut EST library. Of the 10 pancreatic lipase family genes, six appear to encode active lipases and four encode inactive lipases, based on the presence/absence of essential catalytic residues. The four gastric lipase family genes appear to encode active proteins. Phylogenetic analysis of 54 lepidopteran pancreatic lipase proteins resolved the clade into five groups of midgut origin and a sixth of non-midgut lipases. The inactive proteins formed two separate groups with highly conserved mutations. The lepidopteran midgut lipases formed a ninth subfamily of pancreatic lipases. Eighteen insect and human gastric lipases were analysed phylogenetically with only very weak support for any groupings. Gene expression was measured in the larval midgut following feeding on five artificial diets and on apple leaves. The artificial diets contained different levels of triacylglycerol, linoleic acid and cholesterol. Significant changes in gene expression (more than 100-fold for active pancreatic lipases) were observed. All the inactive lipases were also highly expressed. The gastric lipase genes were expressed at lower levels and suppressed in larvae feeding on leaves. Together, protein motif analysis and the gene expression data suggest that, in phytophagous lepidopteran larvae, the pancreatic lipases may function in vivo as galactolipases and phospholipases whereas the gastric lipases may function as triacylglycerol hydrolases. [source]


    Principles of ecotoxicology. by C.H. Walker, S.P. Hopkin, R.M. Sibly, and D. Peakall

    INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 4 2007
    Bruce P. Allen
    No abstract is available for this article. [source]


    99mTc-MIBI imaging for prediction of therapeutic effects of second-generation MDR1 inhibitors in malignant brain tumors

    INTERNATIONAL JOURNAL OF CANCER, Issue 12 2007
    Toshio Sasajima
    Abstract The aim of this study was to explore whether 99mTc-methoxyisobutylisonitrile (99mTc-MIBI) is suitable to elucidate multidrug resistance and prediction of potentiation of antitumor agents by second-generation MDR1 inhibitors (PSC833, MS-209) in malignant brain tumors in rat. Malignant tumor cells (RG2 and C6 gliomas, Walker 256 carcinoma) were incubated with low dose vincristine (VCR) to induce multidrug resistance. MTT assay demonstrated a significant increase of surviving fractions in VCR-resistant sublines compared to those of drug-naive cells. Reverse transcriptase polymerase chain reaction revealed higher expression of MDR1 mRNA in VCR-resistant cells than drug-naive cells in each line. Volume distribution (Vd) of 99mTc-MIBI was negatively correlated with MDR1 mRNA expression among drug-naive and VCR-resistant cells. MDR1 inhibitors decreased surviving fractions and increased Vd of 99mTc-MIBI significantly in VCR-resistant sublines, whereas MDR1 mRNA expression was unchanged. These findings indicate that 99mTc-MIBI efflux was functionally suppressed by MDR1 inhibitors. Autoradiographic images of 99mTc-MIBI revealed higher uptake in drug-naive cells at basal ganglia compared with VCR-resistant cells at the opposite basal ganglia of rats. Oral administration of the second-generation MDR1 inhibitors significantly increased 99mTc-MIBI accumulation of both tumors. Therapeutic effects of VCR with or without the MDR1 inhibitors were also evaluated autoradiographically using 14C-methyl- L -methionine (14C-Met) and MIB-5 index. 14C-Met uptake and MIB-5 index of both tumors treated with VCR following the MDR1 inhibitor treatment significantly decreased compared with tumors treated with VCR alone. Analysis of 99mTc-MIBI accumulation is considered informative for detecting MDR1-mediated drug resistance and for monitoring the therapeutic effects of MDR1 inhibitors in malignant brain tumors. © 2007 Wiley-Liss, Inc. [source]


    Stroma Yoles: their construction and development by Alastair R. Walker

    INTERNATIONAL JOURNAL OF NAUTICAL ARCHAEOLOGY, Issue 1 2006
    COLIN MARTIN
    No abstract is available for this article. [source]


    Philanthropy, social capital or strategic alliance?

    INTERNATIONAL JOURNAL OF NONPROFIT & VOLUNTARY SECTOR MARKETING, Issue 3 2002
    The involvement of senior UK business executives with the voluntary sector, implications for corporate fundraising
    Although corporate fundraising is popular there has been very little discussion in the voluntary sector literature of its context. Using questionnaire data from senior executives representing one-third of the FTSE350 companies, and in-depth interviews with a number of top level business men, this paper reports the first UK survey of the personal involvement of senior executives with charities, voluntary and community organisations,[Walker, C. and Pharoah, C. (2000) ,Making time for charity: A survey of top business leaders' involvement with voluntary organisations', Charities Aid Foundation, Kent.] and pinpoints messages about corporate involvement which may help fundraisers develop corporate fundraising strategies. The data give the first indications of how many of the UK's top business executives give time to charity, how much time they give and what they do. It also addresses what there is to gain for and from the charity, the senior executive and their company. The results present a picture of widespread and enthusiastic involvement of senior executives with the voluntary sector; a picture of both a deep personal commitment and of a strong sense of corporate benefit. The survey also raises several important issues and implications for corporate fundraising: should charities be doing more to attract top executives into an active relationship with them? How can they do this? What are the pros and cons of an alliance between corporate figureheads and charitable organisations; how might this relationship be viewed by the public; and how might it best be managed? This paper draws on the results of the survey to illustrate and discuss these issues. Copyright © 2002 Henry Stewart Publications [source]


    Medication communication: a concept analysis

    JOURNAL OF ADVANCED NURSING, Issue 4 2010
    Elizabeth Manias
    manias e. (2010) Medication communication: a concept analysis. Journal of Advanced Nursing66(4), 933,943. Abstract Title.,Medication communication: a concept analysis. Aim., This paper is a report of a concept analysis of medication communication with a particular focus on how it applies to nursing. Background., Medication communication is a vital component of patient safety, quality of care, and patient and family engagement. Nevertheless, this concept has been consistently taken-for-granted without adequate analysis, definition or clarification in the quality and patient safety literature. Data sources., A literature search was undertaken using bibliographic databases, internet search engines, and hand searches. Literature published in English between January 1988 and June 2009 was reviewed. Walker and Avant's approach was used to guide the concept analysis. Discussion., Medication communication is a dynamic and complex process. Defining attributes consider who speaks, who is silent, what is said, what aspects of medication care are prioritized, the use of body language in conversations, and actual words used. Open communication occurs if there is cooperation among individuals in implementing plans of care. Antecedents involve environmental influences such as ward culture and geographical space, and sociocultural influences such as beliefs about the nature of interactions. Consequences involve patient and family engagement in communication, evidence of appropriate medication use, the frequency and type of medication-related adverse events, and the presence of medication adherence. Empirical referents typically do not reflect specific aspects of medication communication. Conclusion., This concept analysis can be used by nurses to guide them in understanding the complexities surrounding medication communication, with the ultimate goal of improving patient safety, quality of care, and facilitating patient and family engagement. [source]


    Walker Use Affects Timed Up and Go and Gait Speed Measures

    JOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 10 2009
    Lucki Katrin MS
    No abstract is available for this article. [source]


    Bt -maize as a potential trap crop for management of Eldana saccharina Walker (Lep., Pyralidae) in sugarcane

    JOURNAL OF APPLIED ENTOMOLOGY, Issue 4 2007
    M. G. Keeping
    Abstract:, Notwithstanding the introduction of several pest management tactics, the stalk borer Eldana saccharina Walker (Lep., Pyralidae) remains the most serious pest in South African sugarcane. A novel tactic for managing this pest in sugarcane would be the use of a dead-end trap crop that attracts moths for oviposition and curtails subsequent larval development, thereby reducing pest population size. Glasshouse bioassays, in which moths chose to oviposit on maize producing Bacillus thuringiensis Cry1Ab toxin (Bt -maize), non- Bt -maize or sugarcane of two cultivars (borer-resistant and -susceptible), showed that E. saccharina laid significantly more eggs and egg batches per dry leaf and unit mass of dry leaf on maize (Bt or non- Bt) than on either of the cane cultivars. When moths had a choice of ovipositing on 2-, 3-, 4- or 5-month-old maize (Bt and non- Bt), dry leaf number and mass of dry leaf material was significantly correlated with number of eggs and egg batches, indicating that older plants, which carried larger amounts of dry leaf matter, were more attractive for oviposition. Finally, glasshouse assays in which hatching larvae fed on 2.5-, 3.5- and 4.5-month-old Bt and non- Bt -maize plants, showed that the Cry1Ab toxin was effective in killing E. saccharina larvae in all Bt -maize plant growth stages, confirming that Bt -maize fulfilled the third requirement (curtailing larval development) of a dead-end trap crop for this pest. We argue that Bt -maize warrants further testing in the field as a trap crop, both alone and as a component of a ,push,pull' or habitat management system for E. saccharina in sugarcane. [source]


    Silicon-mediated resistance of sugarcane to Eldana saccharina Walker (Lepidoptera: Pyralidae): effects of silicon source and cultivar

    JOURNAL OF APPLIED ENTOMOLOGY, Issue 8 2006
    M. G. Keeping
    Abstract:, The effects of four silicon sources , a USA calcium silicate, a local (South African) calcium silicate, Slagment® and fly ash , on the resistance of sugarcane cultivars (two resistant and two susceptible) to Eldana saccharina Walker (Lepidoptera: Pyralidae) were studied in a potted sugarcane trial. Silicon sources were applied at 5000 or 10 000 kg/ha for the calcium silicates and Slagment; fly ash was applied at 15 000 or 30 000 kg/ha. The greatest increase in plant silicon content (particularly in stalks) was recorded for plants treated with local calcium silicate. Silicon uptake did not vary significantly between the susceptible and resistant cultivars, although the resistant cultivars had inherently higher silicon content than the susceptible ones. Treatment with silicon significantly reduced borer damage and borer performance at the higher treatment level. In general, borer damage and performance decreased with increasing rates of applied silicon and both variables were inversely related with per cent stalk silicon. On average, the higher silicon rate reduced damage by 34% in the susceptible cultivars and by 26% in the resistant cultivars, supporting the argument that susceptible cultivars benefit more from silicon treatments than resistant ones. We propose that calcium silicate amendments could be employed in the integrated, area-wide management of E. saccharina and in the management of soil acidity, both of which are widespread problems in the South African sugar industry. [source]


    Evidence for the importance of odour-perception in the parasitoid Rhopalicus tutela (Walker) (Hym., Pteromalidae)

    JOURNAL OF APPLIED ENTOMOLOGY, Issue 6 2001
    E. M. Pettersson
    Possible host location mechanisms in the chalcid wasp Rhopalicus tutela (Walker) (Hym., Pteromalidae), a parasitoid of the eight-spined spruce bark beetle, Ips typographus (L.) (Col., Scolytidae), were examined. This was carried out in order to repeat and complement former studies on parallel parasitoid,scolytid systems that had contradictory results. Morphological examinations of the parasitoid antennae were made using both scanning and transmission electron microscopy. Possible functions of the sensilla placodea (multiporous plate sensillum), and other sensilla present on the antennae, have been indicated. For the first time, the placoid sensilla in a pteromalid parasitoid have shown porous walls and numerous innervations, which are typical characteristics for chemoreceptors. Previously the placoid sensilla have been suggested to be an infrared receptor. In order to test the chemoreceptive ability of R. tutela females and males, a synthetic reference blend was analysed by combined gas chromatography and electroantennographic detector (GC-EAD). Their sensitivity to host-related volatiles (such as certain pheromone components and oxygenated monoterpenes) was significantly greater than that for host-tree-related compounds (monoterpene hydrocarbons). Employing an infrared thermo-scanner, the current study failed to detect ,hot spots' associated with susceptible hosts beneath the bark. Results from electrophysiology and electron microscopy revealed clear odour-perceptive functions of the parasitoid antennae. These results strongly support the major importance of volatiles in host location by the bark beetle parasitoid R. tutela. [source]


    B. Walker, W. Steffen, J. Canadell & J. Ingram (eds) (1999)

    JOURNAL OF ECOLOGY, Issue 1 2000
    Article first published online: 28 JUN 200
    No abstract is available for this article. [source]


    Influence of plant silicon and sugarcane cultivar on mandibular wear in the stalk borer Eldana saccharina

    AGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2009
    Olivia L. Kvedaras
    Abstract 1,Silicon can increase the resistance of plants to attack by herbivorous insects. The present study aimed to determine the effect of silicon and cultivar on mandibular wear in larvae of the sugarcane stalk borer Eldana saccharina Walker (Lepidoptera: Pyralidae). 2,Four sugarcane cultivars, resistant (N21, N33) and susceptible (N11, N26) to E. saccharina were grown in a pot trial in silicon deficient river sand, with (Si+) and without (Si,) calcium silicate. Individual third-instar larvae were confined on the sugarcane stalk at three known feeding sites (leaf bud, root band and internode) and left to feed for 21 days. 3,Eldana saccharina larval heads were mounted on stubs, with the mandibles oriented horizontally and photographed under a scanning electron microscope. Mandibular wear was measured from the digital images using a quantitative method. 4,Although there was a trend for increased wear in larvae that developed on Si+ cane, no significant effect of silicon, cultivar or site on mandibular wear of E. saccharina was shown. 5,This is the first study to accurately and quantitatively measure the mandibular wear of an insect fed on Si+ plants. [source]


    Consistency of resistance to attack by the green spruce aphid (Elatobium abietinum Walker) in different ontogenetic stages of Sitka spruce

    AGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2003
    S. Harding
    Abstract 1,The susceptibility of different genotypes of 29-year-old Sitka spruce to damage by the green spruce aphid, Elatobium abietinum, was investigated in a progeny trial where aphid damage on individual trees had previously been assessed twice in an earlier stage of ontogenetic development. The progeny trial comprised 14 open-pollinated families originating from a clonal seed orchard that had been established using mature spruce trees selected for aphid resistance. 2,Previous investigations had demonstrated that resistance was inherited by the offspring, and that differences in resistance between progenies of the individual orchard clones were highly significant. 3,Susceptibility to aphid attack was recorded as the percentage loss of previous year's needles. Differences in susceptibility recorded between the juvenile trees were found to persist after the trees had developed into the closed-canopy, sexually reproducing stage. Needle loss of the families was significantly less than that of the reference population of Sitka spruce. 4,Hybrids between Sitka spruce and white spruce were defoliated more heavily than pure Sitka spruce, and the difference increased with age. 5,Family heritability of resistance was estimated as 0.60 compared to 0.73 when the trees were assessed in the juvenile stage. The genetic correlation based on family means between damage in the juvenile and sexually reproducing stand was high (0.83), indicating a high consistency of resistance to the aphid over years and ontogenetic stages. 6,A skewed distribution of defoliation indicated that major genes are involved in the expression of resistance, and that the genetics behind resistance has a nonadditive component. [source]


    Practice development: a concept analysis

    JOURNAL OF NURSING MANAGEMENT, Issue 6 2000
    BSc (Hons), J. Unsworth MSc
    Aims This analysis sets out to explore the nature and scope of the concept of practice development. Background The last 10 years has seen a growing interest in the development of health care practice. However, the exact nature of practice development remains poorly articulated and nebulous. Literature from nursing, medical, accountancy, social work and counselling is used to identify the critical attributes of the concept. Data analysis The analysis uses the techniques developed by Walker & Avant (1995) to collect information on the use of the concept from the literature and to construct cases. Key issues Many of the attributes of practice development are shared by other related concepts such as innovation. However, four critical attributes of practice development were identified and illustrated through case construction. Conclusions An understanding of the nature and scope of practice development is essential if the role of the Practice Development Nurse is to be evaluated. The critical attributes and empirical referents identified in this analysis provide a framework for both role development and evaluation. [source]


    The Effects of Bacillus pumilus, Isolated from Wheat Rhizosphere, on Resistance in Wheat Seedling Roots against the Take-all Fungus, Gaeumannomyces graminis var. tritici

    JOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2007
    E. Sari
    Abstract The aim of this study was to verify that induced resistance was another mechanism through which Bacillus pumilus 7 km can suppress Gaeumannomyces graminis (Sacc.) Von Arx and Oliver var. tritici Walker (Ggt). Also, plant growth-promotion activity of B. pumilus 7 km and its effect on disease severity of take-all were evaluated. Soil was drenched with B. pumilus 7 km and disease severity, root and shoot fresh weights and root and shoot heights were evaluated. The activities of soluble peroxidase (SPOX), ionically cell wall-bound peroxidase (CWPOX), , -1,3-glucanase, , -1,4-glucanase and the contents of total phenolic compounds were also determined. The results indicated that disease severity in the bacterized roots was significantly less than the pathogen control roots. Also this isolate promoted root height, root and shoot fresh weights, compared with the healthy control plants. Wheat plants treated with B. pumilus 7 km showed increased presence of SPOX, CWPOX, , -1,3-glucanase, , -1,4-glucanase and phenolic compounds in bacterized roots challenged with the pathogen. In this treatment, maximum SPOX, , -1,3-glucanase and , -1,4-glucanase activities on day 4 and CWPOX activity on day 8 were recorded. Also, maximum total phenolic concentration on day 6 was recorded. The results suggest that the inhibitory effect of B. pumilus 7 km on the take-all may be related to its ability to enhance defense responses in the wheat roots. [source]


    The History of Articulators: The "Articulator Wars" Phenomenon with Some Circumstances Leading up to It

    JOURNAL OF PROSTHODONTICS, Issue 4 2010
    Edgar N. Starcke DDS
    Abstract At the dawn of the 20th century, all was not well with the practice of "plate prostheses." Removable prosthodontics had been degrading for several decades and was now generally in low esteem, even though there had been many significant advances. W. E. Walker had introduced adjustable condylar guides, George Snow, the facebow, and Carl Christensen, a method for clinically measuring the condylar inclines. Nevertheless, the average practicing dentist was still using simple hinge articulators and was apathetic to the deplorable state of the artificial teeth available; however, this was all going to change dramatically when two dentists, Alfred Gysi and J. Leon Williams, working together between 1910 and 1914, presented to the profession the "Trubyte Artificial Tooth System" that embodied both a typal system for selecting anterior teeth and new posterior occlusal carvings that made possible, for the first time, the articulation of artificial teeth. This incited many of prosthetic dentistry's elite to introduce their own theories of mandibular movement and the articulators that they designed to reflect those theories. The intense debates that ensued, both in the meeting halls and in the literature, were numerous and lasted for decades. At the time, the "Articulator Wars" had both positive and negative consequences. Today, with many of the "Articulator Wars" issues remaining as part of the practice of dentistry, the "Articulator Wars" can be considered a phenomenon of enlightenment. [source]


    The Country in the City: The Greening of the San Francisco Bay Area, by Richard A. Walker

    JOURNAL OF REGIONAL SCIENCE, Issue 1 2009
    Laura A. Watt
    No abstract is available for this article. [source]


    AN ORGANIZED SIGNAL IN SNOWMELT RUNOFF OVER THE WESTERN UNITED STATES,

    JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2000
    D. H. Peterson
    ABSTRACT: Daily-to-weekly discharge during the snowmelt season is highly correlated among river basins in the upper elevations of the central and southern Sierra Nevada (Carson, Walker, Tuolumne, Merced, San Joaquin, Kings, and Kern Rivers). In many cases, the upper Sierra Nevada watershed operates in a single mode (with varying catchment amplitudes). In some years, with appropriate lags, this mode extends to distant mountains. A reason for this coherence is the broad scale nature of synoptic features in atmospheric circulation, which provide anomalous insolation and temperature forcing that span a large region, sometimes the entire western U.S. These correlations may fall off dramatically, however, in dry years when the snowpack is spatially patchy. [source]