bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of life‐state on detectability in a demographic study of the terrestrial orchid Cleistes bifaria
Authors: Kéry Marc , Gregg Katharine B.
Published: June 2003

Most plant demographic studies follow marked individuals in permanent plots. Plots tend to be small, so detectability is assumed to be one for every individual. However, detectability could be affected by factors such as plant traits, time, space, observer, previous detection, biotic interactions, and especially by life‐state.

We used a double‐observer survey and closed population capture–recapture modelling to estimate state‐specific detectability of the orchid Cleistes bifaria in a long‐term study plot of 41.2 m2. Based on AICc model selection, detectability was different for each life‐state and for tagged vs. previously untagged plants. There were no differences in detectability between the two observers.

Detectability estimates (SE) for one‐leaf vegetative, two‐leaf vegetative, and flowering/fruiting states correlated with mean size of these states and were 0.76 (0.05), 0.92 (0.06), and 1 (0.00), respectively, for previously tagged plants, and 0.84 (0.08), 0.75 (0.22), and 0 (0.00), respectively, for previously untagged plants. (We had insufficient data to obtain a satisfactory estimate of previously untagged flowering plants).

Our estimates are for a medium‐sized plant in a small and intensively surveyed plot. It is possible that detectability is even lower for larger plots and smaller plants or smaller life‐states (e.g. seedlings) and that detectabilities < 1 are widespread in plant demographic studies.

State‐dependent detectabilities are especially worrying since they will lead to a size‐ or state‐biased sample from the study plot. Failure to incorporate detectability into demographic estimation methods introduces a bias into most estimates of population parameters such as fecundity, recruitment, mortality, and transition rates between life‐states. We illustrate this by a simple example using a matrix model, where a hypothetical population was stable but, due to imperfect detection, wrongly projected to be declining at a rate of 8% per year.

Almost all plant demographic studies are based on models for discrete states. State and size are important predictors both for demographic rates and detectability. We suggest that even in studies based on small plots, state‐ or size‐specific detectability should be estimated at least at some point to avoid biased inference about the dynamics of the population sampled.
Ecological aspects of seed desiccation sensitivity
Authors: Tweddle John C. , Dickie John B. , Baskin Carol C. , Baskin Jerry M.
Published: June 2003

The ability of seeds to survive desiccation is an important functional trait and is an integral part of plant regeneration ecology. Despite this, the topic has received relatively little attention from ecologists. In this study, we examine the relationships between seed desiccation tolerance and two important aspects of plant regeneration ecology: habitat and dormancy. This is done by comparative analysis of a data set of 886 tree and shrub species from 93 families.

The proportion of species displaying desiccation sensitive seeds declines as the habitat becomes drier, and possibly also cooler, although the latter observation requires cautious interpretation. Desiccation sensitivity is most common in moist, relatively aseasonal vegetation zones, but is infrequent in, though not absent from arid and highly seasonal habitats.

The highest frequency of desiccation sensitivity occurs in non‐pioneer evergreen rain forest trees, although 48% of the species examined have desiccation tolerant seeds. In contrast, all pioneer taxa within the data set have drying tolerant seeds.

Desiccation sensitivity is more frequent in seeds that are non‐dormant on shedding (c. 31%), than dormant (c. 9%). Highest frequencies of drying tolerance occur in seeds with physical or combinational dormancy, at 99% and 100%, respectively.

Although there is an association between non‐dormancy and desiccation sensitivity in both tropical and temperate zones, the relationship does not appear to be causal.

Working from the hypothesis that seed desiccation sensitivity represents a derived state in extant species, we use the results to investigate and discuss possible ecological trade‐offs and associated fitness advantages. These may explain the hypothesized repeated loss of this trait. The frequent association between large seed size and desiccation sensitivity is also considered.
Mire development across the fen–bog transition on the Teifi floodplain at Tregaron Bog, Ceredigion, Wales, and a comparison with 13 other raised bogs
Authors: Hughes P. D. M. , Barber K. E.
Published: June 2003

A literature comparison of 14 radiocarbon‐dated macrofossil records of raised peat bog initiation indicates that there is a relationship between the prevailing climate and the character of the first ombrotrophic vegetation communities at peatland sites in Britain and Ireland.

All that is required for ombrotrophy is the separation of the mire growing surface from the influence of surface and subsurface waters. This could occur via vertical accumulation of the peat mass or a lowering of the water table. The establishment of bog species can be rapid once isolation occurs.

Peatlands may become ombrotrophic in a variety of water table conditions and climatic regimes. There are at least two distinctive routes to ombrotrophy, via a ‘dry‐pioneer oligotrophic community’ or via a ‘wet‐pioneer oligotrophic community’.

Tregaron South‐east Bog does not fit the pattern suggested by the literature comparison. The Fen–Bog Transition (FBT) occurred in a period of increased effective precipitation but the first ombrotrophic community was indicative of relatively dry, ‘hummocky’ bog and a deep or unstable water table.

The transitional poor fen communities at Tregaron South‐east Bog were short‐lived. Sphagnum palustre mire lasted for 90 years compared to 300 years at Bolton Fell Moss in Cumbria, and the FBT was synchronous across much of the bog.

The Tregaron peatland complex has a long history of water table fluctuations as shown by the stratigraphy of the marginal peats.

Channel incision in the River Teifi could have contributed to the development of ‘dry hummock’ pioneer bog in the humid climatic conditions at 7300 cal. BP, by reducing the level of lagg streams.
The effects of spatial pattern of nutrient supply on the early stages of growth in plant populations
Authors: Day K. J. , Hutchings M. J. , John E. A.
Published: June 2003

We report an experimental study of the effects of pattern of nutrient supply on the early stages of growth in populations of Cardamine hirsuta. Populations were grown with nutrients provided in one of four spatial patterns (three heterogeneous and one homogeneous). In the three heterogeneous treatments, nutrient‐rich and nutrient‐poor substrate patches of different sizes were set up in chequerboard patterns, with patches of each type accounting in total for half of the substrate, both by volume and area. All treatments provided the same total quantity of nutrients.

After 31 days of growth, populations in the heterogeneous treatments had produced significantly more root, shoot and total biomass than those in homogeneous conditions. The coefficient of variation in shoot sizes, and the variation in root biomass per unit of substrate, were also significantly greater in populations growing under heterogeneous conditions. In the heterogeneous treatments significantly more than 50% of the biomass was located in nutrient‐rich patches, and this proportion increased significantly as patch size increased.

In heterogeneous treatments, yield of plant parts from nutrient‐rich locations was significantly greater than that of plant parts in nutrient‐poor locations. It was also significantly greater than that recovered from equivalent locations in the homogeneous treatment.

We conclude that the spatial configuration of nutrients significantly affects plant population yield, the spatial distribution of population biomass, and plant size hierarchy during the early stages of population growth, even when total nutrient supply is held constant. We predict that these early effects of heterogeneity will continue to have impacts, not only on size structure, but also on the spatial pattern of mortality and the overall level of mortality, at later stages of population growth.
Effects of water level, shade and time on germination and growth of freshwater marsh plants along a simulated successional gradient
Authors: Kellogg Chev H. , Bridgham Scott D. , Leicht Stacey A.
Published: June 2003

We examined the effect of soil organic content (1.4, 3.6, 7.2% soil C), water level (+2, −1, −4 cm from soil surface) and duration (13 or 33 days) on 10 species that varied in abundance during succession in freshwater marshes. We also determined the effect of shade (0, 40, 80% shade) and soil organic content (1.4 and 7.2% soil C) on germination of six species over 62 days with water 0.5 cm below the soil surface.

Water level consistently affected species germination on both dates. Above‐ground biomass was generally higher with increasing organic content of soil, but shade had little effect on germination or height.

The hydrologic zone in which species were found in the field was a good indicator of the response of germination to hydrology. Both early successional species and species widespread across the successional gradient show similar germination on all organic contents, while later successional species appear to germinate best at higher organic contents.

Successional changes in soils are capable of affecting plant community development, independent of disturbance.
Multiple pathways for woody plant establishment on floodplains at local to regional scales
Authors: Cooper David J. , Andersen Douglas C. , Chimner Rodney A.
Published: June 2003

The structure and functioning of riverine ecosystems is dependent upon regional setting and the interplay of hydrologic regime and geomorphologic processes. We used a retrospective analysis to study recruitment along broad, alluvial valley segments (parks) and canyon segments of the unregulated Yampa River and the regulated Green River in the upper Colorado River basin, USA. We precisely aged 811 individuals of Populus deltoides ssp. wislizenii (native) and Tamarix ramosissima (exotic) from 182 wooded patches and determined the elevation and character of the germination surface for each. We used logistic regression to relate recruitment events (presence or absence of cohort) to five flow and two weather parameters.

Woody plant establishment occurred via multiple pathways at patch, reach and segment scales. Recruitment occurred through establishment on (1) vertically accreting bars in the unregulated alluvial valley, (2) high alluvial floodplain surfaces during rare large flood events, (3) vertically accreting channel margin deposits in canyon pools and eddies, (4) vertically accreting intermittent/abandoned channels, (5) low elevation gravel bars and debris fans in canyons during multi‐year droughts, and (6) bars and channels formed prior to flow regulation on the dammed river during controlled flood events.

The Yampa River's peak flow was rarely included in models estimating the likelihood that recruitment would occur in any year. Flow variability and the interannual pattern of flows, rather than individual large floods, control most establishment.

Regulation of the Green River flow since 1962 has had different effects on woody vegetation recruitment in canyons and valleys. The current regime mimics drought in a canyon setting, accelerating Tamarix invasion whereas in valleys the ongoing geomorphic adjustment of the channel, combined with reduced flow variability, has nearly eliminated Populus establishment.

A single year's flow or a particular pattern of flows over a sequence of years, whether natural or man‐made, produces different recruitment opportunities in alluvial and canyon reaches, in diverse landforms within a particular river reach, and for Populus and Tamarix. The design of flows to restore riparian ecosystems must consider these multiple pathways and adjust the seasonal timing, magnitude and interannual frequency of flows to match the desired outcome.
Numerical studies of optical switching and optical bistability phenomena of nano‐ or meso‐size spheres
Authors: Okamoto T. , Haraguchi M. , Fukui M.
Published: June 2003

We propose the use of numerical calculations of the optical response of nonlinear Kerr‐spheres, modifying the Mie theory. As a numerical example, we use a CuCl sphere coated with a Kerr‐nonlinear sphere, taking into account the excitation of the Z3‐exciton. The results clearly show that optical bistable and/or optical switching devices can be realized on a nano‐ and meso‐size scale when the real part of the dielectric constant of CuCl is negative.
Upconversion fluorescence imaging of erbium‐doped fluoride glass particles by apertureless SNOM
Authors: Fragola A. , Aigouy L. , De Wilde Y. , Mortier M.
Published: June 2003

We have imaged fluorescent erbium‐doped fluoride glass particles by apertureless scanning near‐field optical microscopy. The optical excitation has been performed at λ = 780 nm whereas fluorescence emission has been collected around λ = 550 nm. This process, called upconversion by energy transfer, involves two erbium ions and is not linear. Besides an improvement of the lateral resolution, we have observed on some particles that the fluorescence is not homogeneously distributed, but is rather localized in some zones brighter than others. By making tip approach curves, we have also observed that the amount of fluorescence intensity scattered by the tip is increasing when the tip is approaching the sample surface.
Probing highly confined optical fields in the focal region of a high NA parabolic mirror with subwavelength spatial resolution
Authors: Debus C. , Lieb M. A. , Drechsler A. , Meixner A. J.
Published: June 2003

Parabolic mirrors with a high numerical aperture can be conveniently used to produce highly confined optical fields in the focal region. Furthermore, these fields can have interesting polarization behaviour due to the high numerical aperture. In particular, if the mirror is illuminated with a size matched radially polarized or azimuthally polarized doughnut mode, the electric field has in the focal region almost exclusively a longitudinal or a transverse polarization component. Such field distributions are interesting for applications in confocal or near‐field optical microscopy. Here we present experimental results where we have probed some of these field distributions by raster scanning a fine gold tip in nanometer steps through the focal region and detecting the scattered light intensity. The measured intensity patterns are compared with corresponding vector‐field calculations.
Plasmon‐coupled tip‐enhanced near‐field optical microscopy
Authors: Bouhelier A. , Renger J. , Beversluis M. R. , Novotny L.
Published: June 2003

Near the cut‐off radius of a guided waveguide mode of a metal‐coated glass fibre tip it is possible to couple radiation to surface plasmons propagating on the outside surface of the metal coating. These surface plasmons converge toward the apex of the tip and interfere constructively for particular polarization states of the initial waveguide mode. Calculations show that a radially polarized waveguide mode can create a strong field enhancement localized at the apex of the tip. The highly localized enhanced field forms a nanoscale optical near‐field source.
Current‐sensing scanning near‐field optical microscopy using a metal probe for nanometre‐scale observation of electrochromic films
Authors: Iwata F. , Mikage K. , Sakaguchi H. , Kitao M. , Sasaki A.
Published: June 2003

A novel technique for scanning near‐field optical microscopy capable of point‐contact current‐sensing was developed in order to investigate the nanometre‐scale optical and electrical properties of electrochromic materials. An apertureless bent‐metal probe was fabricated in order to detect optical and current signals at a local point on the electrochromic films. The near‐field optical properties could be observed using the local field enhancement effect generated at the edge of the metal probe under p‐polarized laser illumination. With regard to electrical properties, current signal could be detected with the metal probe connected to a high‐sensitive current amplifier. Using the current‐sensing scanning near‐field optical microscopy, the surface topography, optical and current images of coloured WO3 thin films were observed simultaneously. Furthermore, nanometre‐scale electrochromic modification of local bleaching could be performed using the current‐sensing scanning near‐field optical microscopy. The current‐sensing scanning near‐field optical microscopy has potential use in various fields of nanometre‐scale optoelectronics.
Excitation dynamics in a three‐quantum dot system driven by optical near‐field interaction: towards a nanometric photonic device
Authors: Kobayashi K. , Sangu S. , Shojiguchi A. , Kawazoe T. , Kitahara K. , Ohtsu M.
Published: June 2003

Using density operator formalism, we discuss interdot excitation energy transfer dynamics driven by the optical near‐field and phonon bath reservoir, as well as coherent excitation dynamics of a quantum dot system. As an effective interaction between quantum dots induced by the optical near‐field, the projection operator method gives a renormalized dipole interaction, which is expressed as a sum of the Yukawa functions and is used as the optical near‐field coupling of quantum dots. We examine one‐ and two‐exciton dynamics of a three‐quantum dot system suggesting a nanometric photonic switch, and numerically obtain a transfer time comparable with the recent experimental results for CuCl quantum dots.
Large‐area topography analysis and near‐field Raman spectroscopy using bent fibre probes
Authors: Prikulis J. , Murty K. V. G. K. , Olin H. , Käll M.
Published: June 2003

We present a method for combined far‐field Raman imaging, topography analysis and near‐field spectroscopy. Surface‐enhanced Raman spectra of Rhodamine 6G (R6G) deposited on silver nanoparticles were recorded using a bent fibre aperture‐type near‐field scanning optical microscope (NSOM) operated in illumination mode. Special measures were taken to enable optical normal‐force detection for control of the tip–sample distance. Comparisons between far‐field Raman images of R6G‐covered Ag particle aggregates with topographic images recorded using atomic force microscopy (AFM) indicate saturation effects due to resonance excitation.
Scanning near‐field optical microscopy using semiconductor nanocrystals as a local fluorescence and fluorescence resonance energy transfer source
Authors: Shubeita G. T. , Sekatskii S. K. , Dietler G. , Potapova I. , Mews A. , Basché T.
Published: June 2003

Local fluorescence probes based on CdSe semiconductor nanocrystals were prepared and tested by recording scanning near‐field optical microscopy (SNOM) images of calibration samples and fluorescence resonance energy transfer SNOM (FRET SNOM) images of acceptor dye molecules inhomogeneously deposited onto a glass substrate. Thousands of nanocrystals contribute to the signal when this probe is used as a local fluorescence source while only tens of those (the most apical) are involved in imaging for the FRET SNOM operation mode. The dip‐coating method used to make the probe enables diminishing the number of active fluorescent nanocrystals easily. Prospects to realize FRET SNOM based on a single fluorescence centre using such an approach are briefly described.
Near‐field radiation of bow‐tie antennas and apertures at optical frequencies
Authors: Şendur K. , Challener W.
Published: June 2003

We investigate the ability of the bow‐tie slot antenna to generate intense optical spots below the diffraction limit. A commercially available finite‐difference time‐domain electromagnetic modelling software is used in the numerical simulations. The finite‐difference time‐domain software is first compared to analytical results at optical frequencies to verify its accuracy. We then present numerical simulations for various geometries involving apertures on thin films and the bow‐tie antenna. The transmission efficiency and optical spot size of the bow‐tie antenna are compared with those of rectangular and circular apertures on thin metal films. We also investigate the effects of material composition, frequency, and antenna geometry on the near‐field radiation pattern using numerical simulations.
Scanning near‐field optical microscopy of a cell membrane in liquid
Authors: Höppener C. , Molenda D. , Fuchs H. , Naber A.
Published: June 2003

The applications of scanning near‐field optical microscopy to biological specimens under physiological conditions have so far been very rare since common techniques for a probe–sample distance control are not as well suited for operation in liquid as under ambient conditions. We have shown previously that our own approach for a distance control, based on a short aperture fibre probe and a tuning fork as force sensor in a tapping mode, works well even on soft material in water. By means of an electronic self‐excitation circuit, which compensates for changes of the resonance frequency due to evaporation of liquid, the stability of the force feedback has now been further improved. We present further evidence for the excellent suitability of the tapping‐mode‐like distance control to an operation in liquid, for example, by force‐imaging of double‐stranded DNA. Moreover, we demonstrate that a nuclear envelope in liquid can be imaged with a high optical resolution of ∼70 nm without affecting its structural integrity. Thereby, single nuclear pores in the nuclear envelope with a nearest neighbour distance of ∼120 nm have been optically resolved for the first time.
A versatile multipurpose scanning probe microscope
Authors: Cefalì E. , Patanè S. , Gucciardi P. G. , Labardi M. , Allegrini M.
Published: June 2003

A combined scanning probe microscope has been developed that allows simultaneous operation as a non‐contact/tapping mode atomic force microscope, a scattering near‐field optical microscope, and a scanning tunnelling microscope on conductive samples. The instrument is based on a commercial optical microscope. It operates with etched tungsten tips and exploits a tuning fork detection system for tip/sample distance control. The system has been tested on a p‐doped silicon substrate with aluminium depositions, being able to discriminate the two materials by the electrical and optical images with a lateral resolution of 130 nm.
Study of the focused laser spots generated by various polarized laser beam conditions
Authors: Fu Y. H. , Ho F. H. , Lin W. C. , Liu W.‐C. , Tsai D. P.
Published: June 2003

In this work, three‐dimensional near‐field imaging of the focused laser spot was studied theoretically and experimentally. In the theoretical simulation, we use the electromagnetic equivalent of the vectorial Kirchhoff diffraction integral to calculate the intensity distribution of the focal region, and a high depolarization is found in high numerical aperture systems (NA = 0.85). The experimental set‐up is based on a near‐field scanning optical microscope (NSOM) system. A high‐NA objective lens is used to focus incident light of various polarizations, and a tapered near‐field optical fibre probe of the NSOM system is used to determine the intensity of the focal field. The results show an asymmetric distribution of the focused intensity with the linear polarized laser beam.
Simulation of an aperture in the thick metallic screen that gives high intensity and small spot size using surface plasmon polariton
Authors: Tanaka K. , Tanaka M.
Published: June 2003

The optical wave behaviour around a subwavelength aperture in a thick metallic screen is examined through three‐dimensional computer simulation. Treating the metallic screen as a dielectric slab with complex‐valued permittivity, it is possible to design an aperture that simultaneously provides high intensity and small spot size through the excitation of surface plasmon polaritons on the side walls of the aperture.
Transient optical elements: application to near‐field microscopy
Authors: Simanovskii D. , Palanker D. , Cohn K. , Smith T.
Published: June 2003

We report methods of near‐field infrared microscopy with transient optically induced probes. The first technique – a transient aperture (TA) – uses photoinduced reflectivity in semiconductors to generate a relatively large transient mirror (TM) with a small aperture at its centre. We report the optical properties of the TM and TA and experiments performed on near‐field imaging with the TA. The second technique is based on solid immersion microscopy, in which high resolution is achieved when light is focused inside a solid with a high refractive index. By creating a transient Fresnel lens on the surface of a semiconductor wafer via photoinduction, we were able to form a solid immersion lens (SIL) for use as a near‐field probe. The use of transient probes eliminates the need for mechanical scanning of the lens or sample, and thus provides a much faster scanning rate and the possibility to work with soft and liquid objects.
Photo‐initiated energy transfer in nanostructured complexes observed by near‐field optical microscopy
Authors: Wurtz G. A. , Hranisavljevic J. , Wiederrecht G. P.
Published: June 2003

We report an apertureless near‐field optical study on nanostructured objects formed by J‐aggregates adsorbed on silver (Ag) nanoparticles. Near‐field images reveal that the enhanced near‐field from the dressed particle's (DP) resonantly excited plasmon oscillation is efficiently absorbed by the J‐aggregates. The sensitivity of the near‐field images recorded at the harmonics of the probe vibration frequency suggests that the DP is releasing part of the absorbed energy radiatively upon interaction with the probe. The role of the probe in providing this new radiative relaxation channel is further confirmed as fluorescence from the J‐aggregates on the particle is detected on the particle location only. We based the interpretation of our results on the near‐field optical response from a bare Ag particle excited at the plasmon resonance as well as on far‐field emission and transient absorption experiments.
How light gets through periodically nanostructured metal films: a role of surface polaritonic crystals
Authors: Zayats A. V. , Salomon L. , De Fornel F.
Published: June 2003

The physical origin of the enhanced optical transmission of periodically structured films related to surface plasmon polaritons is discussed from first principles. The enhancement of transmission through smooth, randomly rough and periodically nanostructured films is considered. Analysis shows that any metal (or dielectric) nanostructured film can exhibit enhanced transmission in certain spectral ranges corresponding to surface plasmon (or phonon) polariton Bloch mode states on a periodic structure. Resonant tunnelling via these states is responsible for the transmission enhancement. The properties of surface polaritonic crystals are analogous to those of photonic crystals and can find numerous applications for scaling down optical devices to nanometric dimensions as well as for designing novel nanostructured materials whose optical properties are determined by surface polariton interaction in a periodic structure.
Bessel beams as virtual tips for near‐field optics
Authors: Grosjean T. , Courjon D. , Van Labeke D.
Published: June 2003

In the previous NFO meeting, we proposed the use of confined evanescent light beams as ‘virtual’ or ‘immaterial’ tips. Unfortunately, this technique was hindered by the need for perfectly radially polarized light beams. In this communication, we propose a simple, stable and cheap method allowing the generation of beams of any polarization and more especially of purely radially polarized light beams. We also demonstrate both theoretically and experimentally that for near‐field imaging systems polarization is a limiting factor of resolution and light confinement. Finally, we present the very first experimental results dealing with virtual tips.
Performance of visible and mid‐infrared scattering‐type near‐field optical microscopes
Authors: Taubner T. , Hillenbrand R. , Keilmann F.
Published: June 2003

We describe the principles of two scattering‐type near‐field optical microscopes (s‐SNOMs), one operating at 633 nm wavelength, the other at selectable wavelengths in the range 7.3–11.3 µm, and compare the measurement experience. Both use interferometric detection of scattered radiation, and are therefore capable of amplitude and phase‐contrast imaging. In this study both instruments use the same or even identical commercial probe tips, and measure a single, three‐component, test sample. Our results show that the imaging process of s‐SNOM is wavelength‐independent, namely, that the resolution is determined by the properties of the tip only, and that the contrast is given by the complex refractive index of the sample, predictable from a simple, analytical model of tip–sample interaction. A novel, ‘edge‐darkening’ artefact is described which may appear in s‐SNOM and that is wavelength‐independent.
Experimental studies of surface plasmon polariton band gap effect
Authors: Volkov V. S. , Bozhevolnyi S. I. , Leosson K. , Boltasseva A.
Published: June 2003

Surface plasmon polaritons (SPPs) propagation at a gold film surface covered by periodic arrays of ∼40‐nm‐high scatterers arranged in a triangular lattice of different periods containing straight line defects is studied using collection scanning near‐field optical microscopy. The results reveal the dependence of the SPP band gap (SPPBG) effect manifested via the SPP reflection and guiding (along line defects) on the parameters of the surface structures (period, filling factor and lattice orientation). We find that the SPPBG effect is stronger along ΓK direction for all investigated periodic structures. Our results demonstrate that the SPPBG effect becomes less pronounced with a decrease of the filling factor and disappears for a filling factor close to 0.2. We also observe that the centre of the SPPBG shifts towards longer wavelengths with an increase of the lattice period.
Photoperiodic and temperature control of diapause induction and colour change in the southern green stink bug Nezara viridula
Authors: Musolin Dmitry L. , Numata Hideharu
Published: June 2003

Abstract. The effect of photoperiod and temperature on the duration of the nymphal period, diapause induction and colour change in adults of Nezara viridula (L.) (Heteroptera: Pentatomidae) from Japan was studied in the laboratory. At 20 °C, the developmental period for nymphs was significantly shorter under LD 10 : 14 h (short day) and LD 16 : 8 h (long day) than under intermediate photoperiods, whereas at 25 °C it was slightly shorter under intermediate than short‐ and long‐day conditions. It is assumed that photoperiod‐mediated acceleration of nymphal growth takes place in autumn when day‐length is short and it is unlikely that nymphal development is affected by day‐length under summer long‐day and hot conditions. Nezara viridula has an adult diapause controlled by a long‐day photoperiodic response. At 20 °C and 25 °C in both sexes, photoperiodic responses were similar and had thresholds close to 12.5 h, thus suggesting that the response is thermostable within this range of temperatures and day‐length plays a leading role in diapause induction. Precopulation and preoviposition periods were significantly longer under near‐critical regimes than under long‐day ones. Short‐day and near‐critical photoperiods induced a gradual change of adult colour from green to brown/russet. The rate of colour change was significantly higher under LD 10 : 14 h than under LD 13 : 11 h, suggesting that the colour change is strongly associated with diapause induction. The incidences of diapause or dark colour did not vary among genetically determined colour morphs, indicating that these morphs have a similar tendency to enter diapause and change colour in response to short‐day conditions.
Genotype and temperature influence pea aphid resistance to a fungal entomopathogen
Authors: Stacey David A. , Thomas Matthew B. , Blanford Simon , Pell Judith K. , Pugh Clare , Fellowes Mark D. E.
Published: June 2003

Abstract. The influence of temperature on life history traits of four Acyrthosiphon pisum clones was investigated, together with their resistance to one genotype of the fungal entomopathogen Erynia neoaphidis. There was no difference among aphid clones in development rate, but they did differ in fecundity. Both development rate and fecundity were influenced by temperature, but all clones showed similar responses to the changes in temperature (i.e. the interaction term was nonsignificant). However, there were significant differences among clones in susceptibility to the pathogen, and this was influenced by temperature. Furthermore, the clones differed in how temperature influenced susceptibility, with susceptibility rankings changing with temperature. Two clones showed changes in susceptibility which mirrored changes in the in vitro vegetative growth rate of E. neoaphidis at different temperatures, whereas two other clones differed considerably from this expected response. Such interactions between genotype and temperature may help maintain heritable variation in aphid susceptibility to fungal pathogen attack and have implications for our understanding of disease dynamics in natural populations. This study also highlights the difficulties of drawing conclusions about the efficacy of a biological control agent when only a restricted range of pest genotypes or environmental conditions are considered.
Presence of trehalulose and other oligosaccharides in hemipteran honeydew, particularly Aleyrodidae
Authors: Byrne David N. , Hendrix Donald L. , Williams Livy H.
Published: June 2003

Abstract. Production by a bacterium of the disaccharide trehalulose was reported 30 years ago. The association between the fabrication of trehalulose and Insecta was found more recently. It was initially discovered in the honeydew, excreta, of the whitefly Bemisia tabaci feeding on Euphorbia pulcherrima where it was the predominant sugar. In the present study, B. tabaci‐produced trehalulose was again found in honeydew at significant levels, this time when the whitefly fed on 10 different plants. In seven of 10 Bemisia/host combinations, trehalulose accounted for more than 30% of the total carbohydrates found in their honeydew and was the principal oligosaccharide. Trehalulose constituents, glucose and fructose, were also present at lower levels, as were other oligosaccharides such as melezitose. Feeding by B. tabaci on the three other plant hosts also resulted in the production of trehalulose at relatively high levels (6.1–16.5%). Other whitefly species examined had little (e.g. B. afer and Aleurothrixus spp.), or no trehalulose (e.g. Trialeurodes spp. and Siphoninus phillyreae), in their honeydew. Trehalulose was also found in the honeydew of two aphid and one scale insect species. In insects whose honeydew had low levels or no trehalulose, sucrose, its constituents, or larger sugars predominated. The trisaccharide bemisiose was also found in the honeydew of half the whitefly species examined. Bemisiose was discovered here for the first time in the honeydew of three aphid species and three species of scale insects. Reasons for the production of trehalulose are often linked to high levels of dietary sucrose in whiteflies. This is probably true in our case because cotton and cucurbits, at least, are known to contain a great deal of sucrose. Although other functional possibilities were explored, the data suggest that trehalulose, being less susceptible to hydrolysis than sucrose, is involved in osmoregulation.
Photoperiodic and temperature effects on the intensity of larval diapause inSesamia nonagrioides
Authors: Fantinou Argyro A. , Kourti Anna T. , Saitanis Constantinos J.
Published: June 2003

Abstract.The intensity of larval diapause inSesamia nonagrioidesLef (Lepidoptera: Noctuidae) was investigated under laboratory conditions. Newly hatched larvae were exposed to different stationary photoperiods (from LD 7 : 17 h to LD 14 : 10 h), at a constant temperature of 25 °C. Diapause incidence was higher when larvae were exposed to daylengths shorter than the critical value (LD 12 : 12 h), whereas the within‐treatment variation in the larval period appeared to be significantly correlated with the photoperiod applied. The incidences of diapause and the duration of larval development were also measured after exposing larvae to short photoperiods (LD 8 : 16 h, LD 10 : 14 h or LD 12 : 12 h) in combination with various temperatures (20, 22.5 or 25 °C). Although an increase in the incidence of diapause appeared with the lowering of the temperature, no statistical differences were observed in the time needed for pupation within the photoperiodic treatments at the temperatures of 20 and 22.5 °C. Furthermore, when diapausing larvae were transferred to the long photoperiod of LD 16 : 8 h, they immediately proceeded to pupation, regardless of the photoperiod or the temperature to which they had been previously exposed, indicating that there were no differences in the intensity of diapause. Photoperiodic changes from LD 10 : 14 h to LD 12 : 12 h or to LD 14 : 10 h at different larval ages reduced the intensity of diapause with (a) early age of transfer and (b) increase of daylength. By contrast, when larvae were transferred from the long photoperiod of LD 14 : 10 h to shorter, such as LD 10 : 14 h or LD 12 : 12 h, a small increase in the intensity of diapause with the shortening of the daylength was apparent. These results support the hypothesis that insects may compare the duration of the photoperiod and could classify them as either longer or shorter in relation to the critical value.
Concentration of air‐borne pheromone required for long‐lasting peripheral adaptation in the obliquebanded leafroller, Choristoneura rosaceana
Authors: Stelinski Lukasz L. , Gut Larry J. , Miller James R.
Published: June 2003

Abstract. Electroantennogram (EAG) responses of male obliquebanded leafrollers, Choristoneura rosaceana (Harris), to the main component of its pheromone blend and traces of geometric isomer ((Z)11‐14:Ac and (E)11‐14:Ac, respectively) were recorded before and after 1 h of continuous exposure to pheromone in laboratory experiments, and 24 h of exposure under field conditions. Concentrations of pheromone ranging from 56 to below 1 ng mL−1 air in Teflon chambers with regulated air exchange reduced peripheral sensory responses by 40–60% as measured by amplitudes of the EAG. Adaptation did not increase in a dosage‐dependent fashion over most of this range; an identical reduction of responsiveness was observed at each exposure to an effective concentration. Exposure of C. rosaceana at a loading dosage of 1 ng of pheromone in 100 µL of mineral oil (air concentration below the GLC detection limit) did not induce measurable adaptation. Caging C. rosaceana in apple trees adjacent to one, two or four Isomate OBLR/PLR Plus polyethylene pheromone dispensers for 24 h resulted in long‐lasting adaptation similar to that seen in laboratory experiments. Adaptation was not observed for C. rosaceana caged at a distance of 2 m from Isomate dispensers in 1‐ha plots treated with 500 dispensers per ha. Whenever observed, this type of adaptation was expressed for more than 5 min after exposure to pheromone ceased. Collectively, this adaptation phenomenon in C. rosaceana is consistent with the third of Zufall & Leinders‐Zufall's types of olfactory adaptation that is ‘long‐lasting’. Although the dosage of pheromone required to induce long‐lasting adaptation in this moth is judged high relative to that for normal sexual communication, we suggest this type of adaptation may come into play for some but not all moths under pest‐control regimes using the tactic of pheromone‐disruption, particularly those using high‐dosage release technologies like pheromone rope dispensers or Microsprayers.
Electrophysiological identification of cold receptors on the antennae of the ground beetle Pterostichus aethiops
Authors: Merivee Enno , Vanatoa Alo , Luik Anne , Rahi Märt , Sammelselg Väino , Ploomi Angela
Published: June 2003

Abstract.  In single‐sensillum extracellular electrophysiological recordings, terminal campaniform sensilla at the tip of antennae of the ground beetle Pterostichus aethiops (Pz., 1797) show action potentials of three sensory cells, A‐, B‐ and C‐cells, distinguished by differences in their spike amplitudes. Only the A‐cell, with the largest spike amplitude, is highly sensitive to temperature fluctuations, showing remarkable changes in its firing rate induced by changes in temperature of 0.1 °C. The firing rate of A‐cells at 23 °C varies from 15–52 Hz among different beetles. Mean impulse frequency of A‐cells is found to be a function of steady temperature, the firing rate decreasing with temperature increase. A‐cells respond to a rapid temperature drop with a strong phasic‐tonic reaction; larger decreases in temperature evoke higher peak frequency values. Maximum peak frequencies, varying from 380–630 Hz in different beetles, are induced by temperature decreases of 3–10 °C, whereas temperature rise strongly inhibits impulse activity of the A‐cell. The first manifestation of rapid warming in the nerve impulse sequence is a very long interspike period, followed by diminished activity. Both the length of the long interspike period and the rate of following impulse activity are functions of temperature change; hence, A‐cells respond to temperature changes as typical cold receptors, similar to coeloconic and short hair‐like sensilla in other insects.
A maternal influence on the conditioning to plant cues of Aphidius colemani Viereck, parasitizing the aphid Myzus persicae Sulzer
Authors: Douloumpaka Sophia , Van Emden Helmut F.
Published: June 2003

Abstract. The offspring of parasitoids, Aphidius colemani Viereck, reared on Brussels sprouts and emerging from Myzus persicae Sulzer on a fully defined artificial diet, show no preferences in a four‐way olfactometer, either for the odour of the diet, the odour of Brussels sprouts, or the odour of two other crucifers (cabbage and Chinese cabbage). A similar lack of odour preferences is shown when the host aphids are exposed for parasitization (for 48 h) on cabbage, Chinese cabbage or wheat. However, if parasitization occurs on Brussels sprouts, a weak but statistically highly significant response to Brussels sprout odour is observed. Although as many as 30–35% of the parasitoids show no response to any odour, another 35% respond positively to the odour of Brussels sprout compared with responses to the odours of cabbage, Chinese cabbage or wheat of only approximately 10%. An analagous result is obtained when the parent parasitoids are reared on cabbage. In this case, significant positive responses of their offspring to cabbage odour occur only if the 48‐h parasitization has occurred also on cabbage. However, with parasitoids from Brussels sprouts parasitizing the aphids for 48 h also on Brussels sprouts, the offspring subsequently emerging from pupae excised from the mummies show no preference for Brussels sprout odour. Thus, although the Brussels sprout cue had been experienced early in the development of the parasitoids, they only become conditioned to it when emerging from the mummy. Both male and female parasitoids respond very similarly in all experiments. It is proposed that the chemical cue (probably glucosinolates in these experiments) is most likely in the silk surrounding the parasitoid pupa, and that the mother may leave the chemical in or around the egg at oviposition, inducing chemical defences in her offspring to the secondary plant compounds that the offspring are likely to encounter.
Temperature preferences of the mite, Alaskozetes antarcticus, and the collembolan, Cryptopygus antarcticus from the maritime Antarctic
Authors: Hayward S. A. L. , Worland M. R. , Convey P. , Bale J. S.
Published: June 2003

Abstract. The thermal preferences of Alaskozetes antarcticus (Acari, Cryptostigmata) and Cryptopygus antarcticus (Collembola, Isotomidae) were investigated over 6 h within a temperature gradient (−3 to +13 °C), under 100% relative humidity (RH) conditions. After 10 days of acclimation at −2 or +11 °C, individual supercooling points (SCP) and thermopreferences were assessed, and compared with animals maintained for 10 days under fluctuating field conditions (−6 to +7 °C). Acclimation at −2 °C lowered the mean SCP of both A. antarcticus (−24.2 ± 9.1) and C. antarcticus (−14.7 ± 7.7) compared to field samples (−19.0 ± 9.0 and −10.7 ± 5.2, respectively). Acclimation at +11 °C increased A. antarcticus mean SCP values (−13.0 ± 8.5) relative to field samples, whereas those of C. antarcticus again decreased (−16.7 ± 9.1). Mites acclimated under field conditions or at +11 °C selected temperatures between −3 and +1 °C. After acclimation at −2 °C, both species preferred +1 to +5 °C. Cryptopygus antarcticus maintained under field conditions preferred +5 to +9 °C, whereas individuals acclimated at +11 °C selected +9 to +13 °C. For A. antarcticus, thermopreference was not influenced by its cold hardened state. The distribution of field specimens was further assessed within two combined temperature and humidity gradient systems: (i) 0–3 °C/12% RH, 3–6 °C/33% RH, 6–9 °C/75% RH and 9–12 °C/100% RH and (ii) 0–3 °C/100% RH, 3–6 °C/75% RH, 6–9 °C/33% RH and 9–12 °C/12% RH. In gradient (i), C. antarcticus distributed homogeneously, but, in gradient (ii), C. antarcticus preferred 0–3 °C/100% RH. Alaskozetes antarcticus selected temperatures between 0 and +6 °C regardless of RH conditions. Cryptopygus antarcticus appears better able than A. antarcticus to opportunistically utilize developmentally favourable thermal microclimates, when moisture availability is not restricted. The distribution of A. antarcticus appears more influenced by temperature, especially during regular freeze‐thaw transitions, when this species may select low temperature microhabitats to maintain a cold‐hardened state.
Visual discrimination by the honeybee (Apis mellifera): the position of the common centre as the cue
Authors: Horridge Adrian
Published: June 2003

Abstract. Bees can be trained to discriminate between a target with a 20° spot above a 10° spot of the same colour, and another target with the spots exchanged in position. Tests show that they do not remember the separate positions of spots of the same colour (including black) on the same target. The bees discriminate the difference in positions, in the vertical direction, of the common centres of the spots taken together, with or without green contrast.

Similar results are obtained in discriminations of a fixed T shape, each composed of two broad black bars subtending 8 by 24°, vs the same shape inverted. The trained bees fail to discriminate between the T shapes when the centroids are at the same level in the vertical direction. Moving the shapes in the horizontal direction in tests has less effect. Quite different results are obtained when the two bars of the T shape differ in colour. The bees discriminate the positions of the two colours separately, but they still fail to discriminate the shape of the T. The results can be explained by filters that detect the intensities within their fields, irrespective of shape, and weigh them according to their vertical angles from the horizontal midline. The normal function of these filters could be to detect the levels of objects relative to the horizon when the bee is in flight.