Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Unraveling molecular mechanisms underlying plant defense in response to dual insect attack : studying density-dependent effects
Kroes, A. - \ 2016
University. Promotor(en): Marcel Dicke; Joop van Loon. - Wageningen : Wageningen University - ISBN 9789462577756 - 265 p.
016-3953 - arabidopsis thaliana - insect pests - herbivory - pest resistance - defence mechanisms - insect plant relations - molecular plant pathology - density - insectenplagen - herbivorie - plaagresistentie - verdedigingsmechanismen - insect-plant relaties - moleculaire plantenziektekunde - dichtheid

In the field, plants suffer from attack by herbivorous insects. Plants have numerous adaptations to defend against herbivory. Not only do these defense responses reduce performance of the feeding herbivore, they also result in the attraction of natural enemies of herbivores.

The majority of studies investigating plant-insect interactions addressed mainly the effects of attack by a single herbivore species on induced plant defenses. However, because plants are members of complex communities, plants are exposed to different insect attackers at the same time. Moreover, attacks by different herbivores interact at different levels of biological organization, ranging from the level of gene expression, phytohormone production and biochemical changes up to the individual level. Effects of plant responses to feeding by two or more herbivore species simultaneously might cascade through the community and thereby affect insect community composition.

The induction of plant defense responses is regulated by a network of signaling pathways that mainly involve the phytohormones jasmonic acid (JA), salicylic acid (SA) and ethylene (ET). The signaling pathways of the two phytohormones SA and JA interact antagonistically, whereas JA and ET signaling pathways can interact both synergistically and antagonistically in regulating plant defense responses. In general, JA-mediated signaling underlies defense responses against leaf-chewing herbivores, such as caterpillars, whereas phloem-feeding insects, such as aphids, mainly induce SA-regulated defenses.

When caterpillars and aphids simultaneously feed on the same host plant, crosstalk between phytohormonal signaling pathways may affect the regulation of plant defenses. Consequently, multiple insect herbivores feeding on plants interact indirectly through plant-mediated effects. Studies investigating molecular mechanisms underlying interference by multiple attacking insects with induced plant defenses will benefit studies on the ecological consequences of induced plant responses.

The aim of this thesis was to elucidate molecular mechanisms that underlie plant-mediated interactions between attacking herbivores from different feeding guilds, namely Brevicoryne brassicae aphids and Plutella xylostella caterpillars.

Because herbivore density affects the regulation of plant defense responses, it may also influence the outcome of multiple insect-plant interactions. To study if modulation of induced plant defenses in response to dual insect attack depends on insect density, plants were infested with two densities of aphids.

Responses of Arabidopsis thaliana plants to simultaneous feeding by aphids and caterpillars were investigated by combining analyses of phytohormone levels, defense gene expression, volatile emission, insect performance and behavioral responses of parasitoids. To better predict consequences of interactions between plants and multiple insect attackers for herbivore communities, the regulation of defense responses against aphids and caterpillars was also studied in the ecological model plant wild Brassica oleracea.

Transcriptomic changes of plants during multiple insect attack and their consequences for the plant’s interactions with members of the associated insect community take place at different time scales. Direct correlation of transcriptomic responses with community development is, therefore, challenging. However, detailed knowledge of subcellular mechanisms can provide tools to address this challenge.

One of the objectives of this thesis, therefore, was to investigate the involvement of phytohormonal signaling pathways and their interactions during defense responses against caterpillars or aphids at different densities, when feeding alone or simultaneously on the model plant A. thaliana. The studies show that aphids at different densities interfere in contrasting ways with caterpillar-induced defenses, which required both SA- and JA-signal-transduction pathways. Transcriptional analysis revealed that expression of the SA transcription factor gene WRKY70 was differentially affected upon infestation by aphids at low or high densities. Interestingly, the expression data indicated that a lower expression level of WRKY70 led to significantly higher MYC2 expression through SA-JA crosstalk. Based on these findings, it is proposed that by down-regulating WRKY70 expression, the plant activates JA-dependent defenses which could lead to a higher resistance against aphids and caterpillars.

Plutella xylostella caterpillars also influenced plant defense responses when feeding simultaneously with aphids. Caterpillar feeding affected aphid-induced defenses which had negative consequences for aphid performance. Induction of both ET- and JA-mediated defense responses is required for this interference. Moreover, aphid density also played an important role in the modulation by P. xylostella of aphid-induced defenses: P. xylostella caterpillars induced changes in levels of JA and its biologically active from, JA-Ile, only when feeding simultaneously with aphids at a high density.

To study the overall effect of dual herbivory on induced plant defenses, not only interference with induced direct defense, but also with induced indirect defenses was addressed in A. thaliana. We found a significant preference of the aphid parasitoid Diaeretiella rapae for volatiles from aphid-infested A. thaliana wild-type plants and ein2-1 (ET-insensitive) mutants. Interestingly, simultaneous feeding by P. xylostella caterpillars on wild-type plants increased D. rapae’s preference for odors from aphid-infested plants. However, upon disruption of the ET-signaling pathway, D. rapae did not distinguish between ein2-1 mutants infested by aphids or by both aphids and caterpillars. This showed that intact ET signaling is needed for caterpillar modulation of the attraction of D. rapae parasitoids.

On the other hand, attraction of the caterpillar parasitoid Diadegma semiclausum to volatiles emitted by A. thaliana plants simultaneously infested by caterpillars and aphids was influenced by the density of the feeding aphids. Biosynthesis and emission of the terpene (E,E)-α-farnesene could be linked to the observed preference of D. semiclausum parasitoids for the HIPV blend emitted by plants dually infested by caterpillars and aphids at a high density, compared to dually infested plants with a low aphid density.

Transcriptomic changes in the response of A. thaliana wild-type plants to simultaneous feeding by P. xylostella caterpillars and B. brassicae aphids compared to plants infested by P. xylostella caterpillars alone were assessed using a microarray analysis. I particularly addressed the question whether the transcriptomic response to simultaneously attacking aphids and caterpillars was dependent on aphid density and time since initiation of herbivory. The data show that in response to simultaneous feeding by P. xylostella caterpillars and B. brassicae aphids the number of differentially expressed genes was higher compared to plants on which caterpillars had been feeding alone. Additionally, specific genes were differentially expressed in response to aphids feeding at low or high density. Cluster analysis showed that the pattern of gene expression over the different time points in response to dual infestation was also affected by the density of the attacking aphids. These results suggest that insects attacking at a high density cause an acceleration in plant responses compared to insects attacking at low density.

As a next step in the study of multiple interacting herbivores, I studied whether plant responses to dual herbivory have consequences for the performance of a subsequently arriving herbivore, Mamestra brassicae caterpillars. The ecological consequences of plant responses to dual herbivory cascading into a chain of interactions affecting other community members have remained unstudied so far. We used wild B. oleracea plants to evaluate dual herbivore-induced plant adaptations for subsequent herbivory. We found that simultaneous feeding by P. xylostella and B. brassicae resulted in different plant defense-related gene expression and differences in plant hormone levels compared to single herbivory, and this had a negative effect on subsequently arriving M. brassicae caterpillars. Differential induction of JA-regulated transcriptional responses to dual insect attack was observed which could have mediated a decrease in M. brassicae performance. The induction of plant defense signaling also affected both P. xylostella and B. brassicae performance. This study further helps to understand herbivore community build-up in the context of plant-mediated species interactions.

Altogether, findings from this thesis reveal a molecular basis underlying plant responses against multiple herbivory and provide insight in plant-mediated interactions between aphids and caterpillars feeding on plants growing in the field or used in agriculture.

Estimating the spatial position of marine mammals based on digital camera recordings
Hoekendijk, J.P.A. ; Vries, J. de; Bolt, K. van der; Greinert, J. ; Brasseur, S.M.J.M. ; Camphuysen, C.J. ; Aarts, G.M. - \ 2015
Ecology and Evolution 5 (2015)3. - ISSN 2045-7758 - p. 578 - 589.
porpoises phocoena-phocoena - harbor porpoises - habitat selection - wadden sea - north-sea - marsdiep - inlet - cetaceans - currents - density
Estimating the spatial position of organisms is essential to quantify interactions between the organism and the characteristics of its surroundings, for example, predator-prey interactions, habitat selection, and social associations. Because marine mammals spend most of their time under water and may appear at the surface only briefly, determining their exact geographic location can be challenging. Here, we developed a photogrammetric method to accurately estimate the spatial position of marine mammals or birds at the sea surface. Digital recordings containing landscape features with known geographic coordinates can be used to estimate the distance and bearing of each sighting relative to the observation point. The method can correct for frame rotation, estimates pixel size based on the reference points, and can be applied to scenarios with and without a visible horizon. A set of R functions was written to process the images and obtain accurate geographic coordinates for each sighting. The method is applied to estimate the spatiotemporal fine-scale distribution of harbour porpoises in a tidal inlet. Video recordings of harbour porpoises were made from land, using a standard digital single-lens reflex (DSLR) camera, positioned at a height of 9.59m above mean sea level. Porpoises were detected up to a distance of 3136m (mean 596m), with a mean location error of 12m. The method presented here allows for multiple detections of different individuals within a single video frame and for tracking movements of individuals based on repeated sightings. In comparison with traditional methods, this method only requires a digital camera to provide accurate location estimates. It especially has great potential in regions with ample data on local (a)biotic conditions, to help resolve functional mechanisms underlying habitat selection and other behaviors in marine mammals in coastal areas.
Onderzoek naar betere schatting van de dichtheid van gras- en maiskuilen
Zom, R.L.G. ; Abbink, G.W. ; Schooten, H.A. van - \ 2015
Wageningen : Wageningen UR Livestock Research (Rapport / Wageningen UR Livestock Research 872) - 46
graskuilvoer - kuilvoer - maïskuilvoer - dichtheid - voorraden - veevoeder - voedingswaarde - kuilvoerkwaliteit - lineaire modellen - regressieanalyse - grass silage - silage - maize silage - density - stocks - fodder - nutritive value - silage quality - linear models - regression analysis
This report describes the results of a study on the possibilities to estimate the density of grass en maize silages for calculation of the fodder stock more accurately than the current table values. During ensiling the amount of crop of 104 grass silage clamps, 42 maize silage clamps and 108 big bales (54 round and 54 square) were weighted and after ensiling the dimensions were measured and the chemical composition was analysed. For round and square bales a new regression formula was derived, which estimates the density more accurate than the current table values. It is recommended to calculate the density of round en square bales with the following formula: Density (kg/m3) = 994.81 - 0.5335 x dry matter content (g/kg) - 1.196 x crude fibre content (g/kg ds). For grass en maize silage in clamps and bunker silo’s no new model could be derived which estimated the density more accurately than the current table values.
Influence of human activities on the activity patterns of Japanese sika deer (Cervus nippon) and wild boar (Sus scrofa) in Central Japan
Doormaal, N. van; Ohashi, H. ; Koike, S. ; Kaji, K. - \ 2015
European Journal of Wildlife Research 61 (2015)4. - ISSN 1612-4642 - p. 517 - 527.
agricultural landscapes - habitat selection - human disturbance - roe deer - land-use - forest - prefecture - behavior - density - damage
Human ageing and population decline in Japan are causing agricultural field abandonment and providing new habitats for Japanese sika deer and wild boar. These species have expanded their distribution and increased in abundance across Japan and are causing increased agricultural damage. Effective countermeasures must factor in the behavioural flexibility of sika deer and wild boar. The aim of this study was to examine the effects of hunting and indirect human activities on the activity patterns of sika deer in central Japan and compare these with previous findings on wild boar. Camera traps were used to observe activity patterns of both species and that of humans. Sika deer and wild boar were most active at night during the non-hunting season. Hunting activities significantly reduced sika deer and wild boar activity patterns. In the non-hunting season, nocturnal activity of sika deer increased with decreasing distance to settlement. A similar, but weak response was also observed for wild boar. This study suggests that sika deer and wild boar avoid humans and humandominated areas by being nocturnal. The recent introduction of night hunting might help to control wildlife populations, but monitoring will be necessary to confirm this expectation.
Spatial heterogeneity in stomatal features during leaf elongation: an analysis using Rosa hybrida
Fanourakis, D. ; Heuvelink, E. ; Carvalho, S.M.P. - \ 2015
Functional Plant Biology 42 (2015)8. - ISSN 1445-4408 - p. 737 - 745.
relative air humidity - gas-exchange - elevated co2 - conductance - leaves - size - density - adaptation - ontogeny - growth
Within-leaf heterogeneity in stomatal traits poses a key uncertainty in determining a representative value for the whole leaf. Accounting for this heterogeneity, we studied stomatal initiation on expanding leaves and estimated stomatal conductance (gs) of mature leaves. The entire lamina was evaluated at four percentages of full leaflet elongation (FLE; leaflet length relative to its final length) in Rosa hybrida L. plants grown at 60% relative air humidity (RH), and at 100% FLE following cultivation at elevated (95%) RH. Over 80% of the stomata were initiated between 33 and 67% FLE, whereas stomatal growth mostly occurred afterwards. At 100% FLE, the heterogeneity in stomatal density was the result of uneven stomatal differentiation, while an uneven differentiation of epidermal cells contributed to this variation only at elevated RH. Noticeable within-leaf differences (up to 40%) in gs were calculated at 100% FLE. Avoiding leaflet periphery decreased this heterogeneity. Despite the large promotive effect of elevated RH on stomatal and pore dimensions, the within-leaf variation remained unaffected in all characters, besides pore aperture (and, thus, gs). The noted level of within-leaf variation in stomatal features demands a sampling scheme tailored to the leaf developmental stage, the feature per se and the evaporative demand during growth.
An assessment of the terrestrial mammal communities in forests of Central Panama, using camera-trap surveys
Meyer, N.F.V. ; Esser, H.J. ; Moreno, R. ; Langevelde, F. van; Liefting, Y. ; Ros Oller, D. ; Vogels, C.B.F. ; Carver, A.D. ; Nielsen, C.K. ; Jansen, P.A. - \ 2015
Journal for Nature Conservation 26 (2015). - ISSN 1617-1381 - p. 28 - 35.
rain-forest - habitat fragmentation - conservation status - neotropical forest - atlantic forest - tayassu-pecari - abundance - biodiversity - landscape - density
The Isthmus of Panama, part of the planet’s third largest megadiversity hotspot, and connecting the faunas of North and South America, has lost more than half of its forest due to agriculture and economicdevelopment. It is unknown to what degree the remaining forest, which is fragmented and subject topoaching, still supports the wildlife diversity found in intact forests. Here, we use camera-trap surveysto assess whether forests in Central Panama, the narrowest and most disturbed portion of the Isthmus,still have intact communities of medium- and large-bodied terrestrial mammals. During 2005–2014,we collected camera-trap survey data from 15 national parks and forest fragments on both sides ofthe Panama Canal, and compared these to similar data from two sites in the intact Darién NationalPark in Eastern Panama, the nearest available reference. We found that most sites in Central Panama– including some of the national parks – had lower mammal species richness and evenness than thereference sites, and less structurally-complex mammal communities. Forests in Central Panama had littleor no apex predators and large terrestrial frugivores, with the exception of two sites directly connectedto the reference site. Our results indicate that the terrestrial mammal community in forests of CentralPanama is currently degraded, even inside national parks. These data provide a baseline for evaluating the success of conservation efforts to prevent the Panamanian Isthmus to become a bottleneck for movement of aniamls
Site-specific dynamics in remnant populations of Northern Wheatears Oenanthe oenanthe in the Netherlands
Oosten, H.H. van; Turnhout, C. van; Hallmann, C.A. ; Majoor, F. ; Roodbergen, M. ; Schekkerman, H. ; Versluijs, R. ; Waasdorp, S. ; Siepel, H. - \ 2015
Ibis 157 (2015)1. - ISSN 0019-1019 - p. 91 - 102.
spatial synchrony - environmental correlation - scale - dispersal - birds - immigration - landscape - density - impact - space
Dynamics of populations may be synchronized at large spatial scales, indicating driving forces acting beyond local scales, but may also vary locally as a result of site-specific conditions. Conservation measures for fragmented and declining populations may need to address such local effects to avoid local extinction before measures at large spatial scales become effective. To assess differences in local population dynamics, we aimed to determine the demographic drivers controlling population trends in three remaining populations of the Northern Wheatear Oenanthe oenanthe in the Netherlands, as a basis for conservation actions. An integrated population model (IPM) was fitted to field data collected in each site in 2007–2011 to estimate fecundity, survival and immigration. Sites were 40–120 km apart, yet first-year recruits were observed to move between some of the sites, albeit rarely. All three populations were equally sensitive to changes in fecundity and first-year survival. One population was less sensitive to adult survival but more sensitive to immigration. A life table response experiment suggested that differences in immigration were important determinants of differences in population growth between sites. Given the importance of immigration for local dynamics along with high philopatry, resulting in low exchange between sites, creating a metapopulation structure by improving connectivity and the protection of local populations are important for the conservation of these populations. Site-specific conservation actions will therefore be efficient and, for the short term, we propose different site-specific conservation actions.
Adsorption of charged and neutral polymer chains on silica surfaces: The role of electrostatics, volume exclusion, and hydrogen bonding
Spruijt, E. ; Biesheuvel, P.M. ; Vos, W.M. de - \ 2015
Physical Review. E, Statistical nonlinear, and soft matter physics 91 (2015). - ISSN 2470-0045 - 11 p.
polyelectrolyte adsorption - double-layer - free-energy - poly(vinylpyrrolidone) - relaxation - desorption - stability - kinetics - colloids - density
We develop an off-lattice (continuum) model to describe the adsorption of neutral polymer chains and polyelectrolytes to surfaces. Our continuum description allows taking excluded volume interactions between polymer chains and ions directly into account. To implement those interactions, we use a modified hard-sphere equation of state, adapted for mixtures of connected beads. Our model is applicable to neutral, charged, and ionizable surfaces and polymer chains alike and accounts for polarizability effects of the adsorbed layer and chemical interactions between polymer chains and the surface. We compare our model predictions to data of a classical system for polymer adsorption: neutral poly(N-vinylpyrrolidone) (PVP) on silica surfaces. The model shows that PVP adsorption on silica is driven by surface hydrogen bonding with an effective maximum binding energy of about 1.3kBT per PVP segment at low pH. As the pH increases, the Si-OH groups become increasingly dissociated, leading to a lower capacity for H bonding and simultaneous counterion accumulation and volume exclusion close to the surface. Together these effects result in a characteristic adsorption isotherm, with the adsorbed amount dropping sharply at a critical pH. Using this model for adsorption data on silica surfaces cleaned by either a piranha solution or an O2 plasma, we find that the former have a significantly higher density of silanol groups.
Disentangling above- and belowground neighbor effects on the growth, chemistry and arthropod community on a focal plant
Kos, M. ; Bukovinszky, T. ; Mulder, P.P.J. ; Bezemer, T.M. - \ 2015
Ecology 96 (2015)1. - ISSN 0012-9658 - p. 164 - 175.
soil feedback - associational susceptibility - vegetational diversity - competition - herbivores - root - resistance - responses - fertilization - density
Neighboring plants can influence arthropods on a focal plant and this can result in associational resistance or associational susceptibility. These effects can be mediated by above- and belowground interactions between the neighbor and focal plant, but determining the relative contribution of the above- and belowground effects remains an open challenge. We performed a common garden experiment with a design that enabled us to disentangle the above- and belowground effects of five different plant species on the growth and chemistry of the focal plant ragwort (Jacobaea vulgaris), and the arthropod community associated to this plant. Aboveground effects of different neighboring plant species were more important for the growth and quality of J. vulgaris and for the arthropod abundance on this plant than belowground effects of neighbors. This remained true when only indirect neighbor effects (via affecting the biomass or quality of the focal plant) were considered. The aboveground neighbor effects on arthropod abundance on the focal plant were strongly negative. However, the magnitude of the effect depended on the identity of the neighboring species, and herbivore abundance on the focal plant was higher when surrounded by conspecific than by heterospecific plants. We also observed interactions between above- and belowground neighbor effects, indicating that these effects may be non-additive. We conclude that above- and belowground associational effects are not equally strong, and that neighbor effects on plant-arthropod interactions occur predominantly aboveground.
Movement Behaviour of the Carabid Beetle Pterostichus melanarius in Crops and a Habitat Interface Explains Patterns of Population Redistribution in the Field
Allema, B. ; Werf, W. van der; Lenteren, J.C. van; Hemerik, L. ; Rossing, W.A.H. - \ 2014
PLoS One 9 (2014)12. - ISSN 1932-6203 - 20 p.
coleoptera carabidae - generalist predators - diffusion-model - dispersal - edges - dynamics - density - slugs
Animals may respond to habitat quality and habitat edges and these responses may affect their distribution between habitats. We studied the movement behaviour of a ground-dwelling generalist predator, the carabid beetle Pterostichus melanarius (Illiger). We performed a mark-recapture experiment in two adjacent habitats; a large plot with oilseed radish (Raphanus sativus) and a plot with rye (Secale cereale). We used model selection to identify a minimal model representing the mark-recapture data, and determine whether habitat-specific motility and boundary behaviour affected population redistribution. We determined movement characteristics of P. melanarius in laboratory arenas with the same plant species using video recording. Both the field and arena results showed preference behaviour of P. melanarius at the habitat interface. In the field, significantly more beetles moved from rye to oilseed radish than from radish to rye. In the arena, habitat entry was more frequent into oilseed radish than into rye. In the field, movement was best described by a Fokker-Planck diffusion model that contained preference behaviour at the interface and did not account for habitat specific motility. Likewise, motility calculated from movement data using the Patlak model was not different between habitats in the arena studies. Motility (m2 d-1) calculated from behavioural data resulted in estimates that were similar to those determined in the field. Thus individual behaviour explained population redistribution in the field qualitatively as well as quantitatively. The findings provide a basis for evaluating movement within and across habitats in complex agricultural landscapes with multiple habitats and habitat interfaces.
Agricultural policies exacerbate honeybee pollination service supply-demand mismatches across Europe
Breeze, T. ; Vaissiere, B.E. ; Bommarco, R. ; Petanidou, T. ; Seraphides, N. ; Kozak, L. ; Scheper, J.A. ; Biesmeijer, J.C. ; Kleijn, D. ; Gyldenkaerne, S. - \ 2014
PLoS One 9 (2014)1. - ISSN 1932-6203 - 8 p.
ecosystem services - fruit-set - sequential introduction - bee abundance - declines - crops - colonies - density - enhance - biodiversity
Declines in insect pollinators across Europe have raised concerns about the supply of pollination services to agriculture. Simultaneously, EU agricultural and biofuel policies have encouraged substantial growth in the cultivated area of insect pollinated crops across the continent. Using data from 41 European countries, this study demonstrates that the recommended number of honeybees required to provide crop pollination across Europe has risen 4.9 times as fast as honeybee stocks between 2005 and 2010. Consequently, honeybee stocks were insufficient to supply >90% of demands in 22 countries studied. These findings raise concerns about the capacity of many countries to cope with major losses of wild pollinators and highlight numerous critical gaps in current understanding of pollination service supplies and demands, pointing to a pressing need for further research into this issue.
Blood feeding on large grazers affects the transmission of Borrelia burgdorferi sensu lato by Ixodes ricinus
Pacilly, F.C.A. ; Benning, M.E. ; Jacobs, F. ; Leidekker, J. ; Sprong, H. ; Wieren, S.E. van; Takken, W. - \ 2014
Ticks and Tick-borne Diseases 5 (2014)6. - ISSN 1877-959X - p. 810 - 817.
lyme borreliosis - tick infestation - north-america - endemic area - roe deer - netherlands - prevalence - density - disease - abundance
The presence of Ixodes ricinus and their associated Borrelia infections on large grazers was investigated. Carcases of freshly shot red deer, mouflon and wild boar were examined for the presence of any stage of I. ricinus. Questing ticks were collected from locations where red deer and wild boar are known to occur. Presence of Borrelia burgdorferi s.l. DNA was examined in a fraction of the collected ticks. Larvae, nymphs and adult ticks were found on the three large grazers. Red deer had the highest tick burden, with many of the nymphs and adult females attached for engorgement. Most larvae had not attached. The mean number of ticks on the animals varied from 13 to 67. Ticks were highly aggregated amongst the animals: some animals had no ticks, while others had high numbers. Larvae and nymphs were mostly found on the ears, while adult ticks were attached to the axillae. The Borrelia infection rate of questing nymphs was 8.5%. Unengorged wandering nymphs on deer had a Borrelia infection rate of 12.5%, while only 0.9% of feeding nymphs carried a Borrelia infection. The infection rate of unengorged adult male ticks was 4.5%, and that of feeding female ticks was 0.7%. The data suggest that ticks feeding on red deer and wild boar lose their Borrelia infections. The implications of the results are discussed with respect to Borrelia epidemiology and maintenance of a Borrelia reservoir as well as the role of reproductive hosts for Ixodes ricinus.
Adhesion and friction properties of fluoropolymer brushes: On the tribological inertness of fluorine
Bhairamadgi, N.S. ; Pujari, S.P. ; Rijn, C.J.M. van; Zuilhof, H. - \ 2014
Langmuir 30 (2014)42. - ISSN 0743-7463 - p. 12532 - 12540.
poly(methyl methacrylate) brushes - self-lubricating composites - organic mono layers - polymer brushes - silicon(111) surfaces - assembled monolayers - coatings - density - films - wear
The effects of fluorination on the adhesion and friction properties of covalently bound poly(fluoroalkyl methacrylate) polymer brushes (thickness ~80 nm) were systematically investigated. Si(111) surfaces were functionalized with a covalently bound initiator via a thiol–yne click reaction to have a high surface coverage for initiator immobilization. Surface-initiated atom-transfer radical polymerization (SI-ATRP) was employed for the synthesis of four different fluoropolymer brushes (SPFx, where x = 0, 3, 7, or 17 F atoms per monomer), based on fluoroalkyl methacrylates. All polymer brushes were characterized with static contact angle measurements, X-ray photoelectron spectroscopy (XPS), and infrared absorption reflection spectroscopy (IRRAS). The polymer brushes exhibited an excellent hydrophobicity, with static water contact angles of up to 121° depending on the number of fluorine atoms per side chain in fluoroalkyl methacrylate. The degree of swelling was precisely studied by using ellipsometry in different solvents such as acetone, hexadecane, hexafluoroisopropanol, nonafluorobutyl methyl ether, and Fluorinert FC-40. The polymer brushes have shown nanoscale swelling behavior in all solvents except hexadecane. The grafting density decreased upon increasing fluorine content in polymer brushes from 0.65 chains/nm2 (SPF0) to 0.10 chains/nm2 (SPF17) as observed in Fluorinert FC-40 as a good solvent. Adhesion and friction force measurements were conducted with silica colloidal probe atomic force microscopy (CP-AFM) under ambient, dry (argon), and lubricating fluid conditions. SPF17 showed the lowest coefficient of friction 0.005 under ambient condition (RH = 44 ± 2%) and a further decrease with 50% under fluidic conditions. These polymer brushes also showed adhesion forces as low as 6.9 nN under ambient conditions, which further went down to 0.003 nN under fluidic conditions (Fluorinert FC-40 and hexadecane) at 10 nN force.
Special issue: WSE symposium: Wood growth under environmental changes: the need for a multidisciplinary approach
Battipaglia, G. ; Micco, V. De; Sass-Klaassen, U.G.W. ; Tognetti, R. ; Mäkelä, A. - \ 2014
Tree Physiology 34 (2014)8. - ISSN 0829-318X - p. 787 - 791.
water-use efficiency - climate-change - drought - xylem - transport - density
Lessons from long-term predator control: a case study with the red fox
Kirkwood, R.J. ; Sutherland, D.R. ; Murphy, S. ; Dann, P. - \ 2014
Wildlife Research 41 (2014). - ISSN 1035-3712 - p. 222 - 232.
vulpes-vulpes-l - wallaby population-dynamics - penguins eudyptula-minor - south-eastern australia - phillip-island - rural britain - home-range - victoria - impact - density
Context: Predator-control aims to reduce an impact on prey species, but efficacy of long-term control is rarely assessed and the reductions achieved are rarely quantified. Aims: We evaluated the changing efficacy of a 58-year-long campaign against red foxes (Vulpes vulpes) on Phillip Island, a 100-km2 inhabited island connected to the Australian mainland via a bridge. The campaign aimed to eliminate the impact of foxes on ground-nesting birds, particularly little penguins (Eudyptula minor). Methods: We monitored the success rate of each fox-control technique employed, the level of effort invested if available, demographics of killed foxes, the numbers of penguins killed by foxes and penguin population size. Key results: The campaign began as a bounty system that ran for 30 years and was ineffective. It transitioned into a coordinated, although localised, control program from 1980 to 2005 that invested considerable effort, but relied on subjective assessments of success. Early during the control period, baiting was abandoned for less effective methods that were thought to pose fewer risks, were more enjoyable and produced carcasses, a tangible result. Control was aided by a high level of public awareness, by restricted fox immigration, and by a clear, achievable and measurable target, namely, to prevent little penguin predation by foxes. Carcasses did prove valuable for research, revealing the genetic structure and shifts in fox demographics. The failure of the program was evident after scientific evaluation of fox population size and ongoing fox impacts. In 2006, the campaign evolved into an eradication attempt, adopting regular island-wide baiting, and since then, has achieved effective knock-down of foxes and negligible predation on penguins. Conclusions: Effective predator control was achieved only after employing a dedicated team and implementing broad-scale baiting. Abandoning widespread baiting potentially delayed effective control for 25 years. Furthermore, both predator and prey populations should be monitored concurrently because the relationship between predator abundance and impact on prey species is not necessarily density dependent. Implications: Critical to adopting the best management strategy is evaluating the efficacy of different methods independently of personal and public biases and having personnel dedicated solely to the task.
Fitness consequences of larval exposure to Beauveria bassiana on adults of the malaria vector Anopheles stephensi
Vogels, C.B.F. ; Bukhari, T. ; Koenraadt, C.J.M. - \ 2014
Journal of Invertebrate Pathology 119 (2014). - ISSN 0022-2011 - p. 19 - 24.
fungus metarhizium-anisopliae - entomopathogenic fungus - mosquito larvae - nosema-algerae - biocontrol agents - gambiae - infection - density - survival - field
Entomopathogenic fungi have shown to be effective in biological control of both larval and adult stages of malaria mosquitoes. However, a small fraction of mosquitoes is still able to emerge after treatment with fungus during the larval stage. It remains unclear whether fitness of these adults is affected by the treatment during the larval stage and whether they are still susceptible for another treatment during the adult stage. Therefore, we tested the effects of larval exposure to the entomopathogenic fungus Beauveria bassiana on fitness of surviving Anopheles stephensi females. Furthermore, we tested whether larval exposed females were still susceptible to re-exposure to the fungus during the adult stage. Sex ratio, survival and reproductive success were compared between non-exposed and larval exposed A. stephensi. Comparisons were also made between survival of non-exposed and larval exposed females that were re-exposed to B. bassiana during the adult stage. Larval treatment did not affect sex ratio of emerging mosquitoes. Larval exposed females that were infected died significantly faster and laid equal numbers of eggs from which equal numbers of larvae hatched, compared to non-exposed females. Larval exposed females that were uninfected had equal survival, but laid a significantly larger number of eggs from which a significantly higher number of larvae hatched, compared to non-exposed females. Larval exposed females which were re-exposed to B. bassiana during the adult stage had equal survival as females exposed only during the adult stage. Our results suggest that individual consequences for fitness of larval exposed females depended on whether a fungal infection was acquired during the larval stage. Larval exposed females remained susceptible to re-exposure with B. bassiana during the adult stage, indicating that larval and adult control of malaria mosquitoes with EF are compatible.
Axillary budbreak in a cut rose crop as influenced by light intensity and red:far-red ratio at bud level
Wubs-Timmermans, A.M. ; Heuvelink, E. ; Marcelis, L.F.M. ; Buck-Sorlin, G.H. ; Vos, J. - \ 2014
Journal of the American Society for Horticultural Science 139 (2014)2. - ISSN 0003-1062 - p. 131 - 138.
photosynthetic photon flux - growth - temperature - shoots - plants - interception - architecture - arabidopsis - responses - density
When flower-bearing shoots in cut rose (Rosa ·hybrida) are harvested, a varying number of repressed axillary buds on the shoot remainder start to grow into new shoots (budbreak). Earlier experiments indicated that light reaching the bud affected the number of budbreaks. In all these studies, whole plants were illuminated with different light intensities or light spectra. The aim of this article is to disentangle the effects of light intensity and light spectrum, in this case red:far-red ratio, at the level of the buds on budbreak in a rose crop. Three experiments were conducted in which light intensity and red:far-red ratio at the level of the buds were independently varied, whereas intensity and red:far-red ratio of incident light on the crop were not changed. Light intensity and red:far-red ratio at the position of the buds were quantified and related to budbreak on the shoot remainders. Removal of vertical shoots increased light intensity and red:far-red ratio as well as budbreak (1.9 budbreaks per shoot remainder compared with 0.4 budbreaks when five vertical shoots were present). No vertical shoots and red light-absorbing shading paper over the plant base mimicked the effect of vertical shoots with respect to light intensity and red:far-red ratio, but budbreak (1.0 budbreaks) was intermediate compared with treatments with and without shoots. This suggested that the presence of shoots exerts an inhibiting effect on budbreak through both effects on light at the bud and correlative inhibition. When plants had no vertical shoots and light intensity and red:far-red ratio at bud level were changed by neutral and red light-absorbing shading paper, there was a positive effect of light intensity on budbreak (0.3 more budbreaks per shoot remainder) and no effect of red:far-red ratio. Combinations of high and low light intensity with high and low red:far-red ratio on axillary buds showed that there was a positive effect of light intensity on budbreak (0.5 more budbreaks per shoot remainder) and no effect of red:far-red ratio. Our study reveals that when light intensity and red:far-red ratio received by the plant are similar but differ at bud level, budbreak was affected by light intensity and not by red:far-red ratio.
The effect of harvesting on biomass production and nutrient removal in phototrophic biofilm reactors for effluent polishing
Boelee, N.C. ; Janssen, M. ; Temmink, H. ; Taparaviciute, L. ; Khiewwijit, R. ; Janoska, A. ; Buisman, C.J.N. ; Wijffels, R.H. - \ 2014
Journal of Applied Phycology 26 (2014)3. - ISSN 0921-8971 - p. 1439 - 1452.
afvalwaterbehandeling - biofilms - dikte - dichtheid - algen - biologische waterzuiveringsinstallaties - fototropie - stikstof - fosfor - verwijdering - biobased economy - waste water treatment - thickness - density - algae - biological water treatment plants - phototropism - nitrogen - phosphorus - removal - waste-water treatment - photosynthetic efficiency - chlorella-sorokiniana - microalgal biofilms - phosphorus removal - mass-transport - fresh-water - light - growth
An increasing number of wastewater treatment plants require post-treatment to remove residual nitrogen and phosphorus. This study investigated various harvesting regimes that would achieve consistent low effluent concentrations of nitrogen and phosphorus in a phototrophic biofilm reactor. Experiments were performed in a vertical biofilm reactor under continuous artificial lighting and employing artificial wastewater. Under similar conditions, experiments were performed in near-horizontal flow lanes with biofilms of variable thickness. It was possible to maintain low nitrogen and phosphorus concentrations in the effluent of the vertical biofilm reactor by regularly harvesting half of the biofilm. The average areal biomass production rate achieved a 7 g dry weight m-2 day-1 for all different harvesting frequencies tested (every 2, 4, or 7 days), corresponding to the different biofilm thicknesses. Apparently, the biomass productivity is similar for a wide range of biofilm thicknesses. The biofilm could not be maintained for more than 2 weeks as, after this period, it spontaneously detached from the carrier material. Contrary to the expectations, the biomass production doubled when the biofilm thickness was increased from 130 µm to 2 mm. This increased production was explained by the lower density and looser structure of the 2 mm biofilm. It was concluded that, concerning biomass production and labor requirement, the optimum harvesting frequency is once per week.
Habitat functionality for the ecosystem service of pest control: reproduction and feeding sites of pests and natural enemies
Bianchi, F.J.J.A. ; Schellhorn, N.A. ; Cunningham, S.A. - \ 2013
Agricultural and Forest Entomology 15 (2013)1. - ISSN 1461-9555 - p. 12 - 23.
agricultural landscapes - coccinellidae - agroecosystems - biodiversity - assemblages - coleoptera - density - aphids - sinks
1 Landscape management for enhanced natural pest control requires knowledge of the ecological function of the habitats present in the landscape mosaic. However, little is known about which habitat types in agricultural landscapes function as reproduction habitats for arthropod pests and predators during different times of the year. 2 We studied the arthropod assemblage on six crops and on the seven most abundant native plant species in two landscapes over 1 year in Australia. Densities of immature and adult stages of pests and their predators were assessed using beat sheet sampling. 3 The native plants supported a significantly different arthropod assemblage than crops. Native plants had higher predator densities than crops over the course of the year, whereas crops supported higher pest densities than the native plants in two out of four seasonal sampling periods. Crops had higher densities of immature stages of pests than native plants in three of four seasonal sampling periods, implying that crops are more strongly associated with pest reproduction than native plants. Densities of immature predators, excluding spiders, were not different between native plants and crops. Spiders were, however, generally abundant and densities were higher on native plants than on crops but, because some species disperse when immature, there is less certainty in identifying their reproduction habitat. 4 Because the predator to pest ratio on native plant species showed little variation, and spatial variation in arthropod assemblages was limited, the predator support function of native vegetation may be a general phenomenon. Incentives that maintain and restore native remnant vegetation can increase the predator to pest ratio at the landscape scale, which could enhance pest suppression in crops.
Clean energy generation using capacitive electrodes in reverse electrodialysis
Vermaas, D.A. ; Bajracharya, S. ; Bastos Sales, B. ; Saakes, M. ; Hamelers, B. ; Nijmeijer, K. - \ 2013
Energy & Environmental Science 6 (2013)2. - ISSN 1754-5692 - p. 643 - 651.
sustainable power-generation - pressure-retarded osmosis - salinity gradients - water - density - difference
Capacitive reverse electrodialysis (CRED) is a newly proposed technology to generate electricity from mixing of salt water and fresh water (salinity gradient energy) by using a membrane pile as in reverse electrodialysis (RED) and capacitive electrodes. The salinity difference between salt water and fresh water generates a potential difference over ion selective membranes, which can be used as a renewable power source. The strength and unique characteristic of CRED in comparison to the other technologies is that it allows multiple membrane cells between a single set of electrodes and at the same time avoids redox reactions using capacitive electrodes. The capacitive electrodes use activated carbon on a support of Ti/Pt mesh to store ions and their charge. A periodic switching of the feed waters, combined with a switching of the direction of the electric current, ensures that the capacitive electrodes do not get saturated. The large membrane pile enables the electrodes to be charged more than in previous approaches for capacitive mixing. As a consequence, the energy cycle of CRED has a larger range in both voltage and accumulated charge compared to previous capacitive mixing technologies. The power density obtainable with CRED stacks with capacitive electrodes is an order of magnitude higher than in previous attempts for capacitive energy extraction and close to or even better than similar RED stacks with conventional redox based electrode systems. CRED is considered to be a stable, safe, clean and high performing technology to obtain energy from mixing of salt water and fresh water.
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