PCR detection of MLOs in quick decline-affected pear trees in Italy

Polymerase chain reaction (PCR) amplification, using primers derived from the 16S rRNA gene, followed by restriction fragment length polymorphism (RFLP) analysis with Alu I restriction endonuclease was used to detect myc-oplasma-like organisms (MLOs) associated with pear decline. MLOs were consistently detected in pear trees that suddenly wilted and died within a few days during summer, as well as in pears of the same orchards with symptoms similar to the slow form of pear decline. In both cases the same RFLP pattern was obtained. Declining pear trees were 5 to 8-yr-old cvs Williams, Kaiser and Max Red Bartlett grafted on to Pyrus communis seedling rootstocks. All the orchards affected by quick decline had severe attacks of pear psyllid (Cacopsylla pyri) during the year this study was performed and during the previous year. The results showed the suitability of DNA amplification by the polymerase chain reaction for the detection of pear decline MLOs and established that MLOs can be detected in infected tissues of dead trees.     

Preliminary caged‐field trial,using the fungal pathogen Zoophthora radicans brefeld (zygomycetes: entomophthorales) against the diamondback moth Plutella xylostella L. (lepidoptera: Yponomeutidae) in the UK

Zoophthora radicans Brefeld was tested for control of Plutella xylostella L. in a caged‐field trial. No infection was seen in control cages, but between 36% and 68% of larvae in live samples, and 38% and 55% of larvae at the final harvest, were infected in inoculated cages, suggesting the biological control potential of this fungus.     

Resource limitation and the lethal and sublethal effects of a viral pathogen in the Indian meal moth, Plodia interpunctella

Abstract.

• 1 The effects of resource limitation and the lethal and sublethal effects of a granulosis virus on a lepidopteran host, the Indian meal moth, Plodia interpunctella, were examined.
• 2 The food quality was manipulated by the addition of an inert bulking agent (methyl cellulose) which caused the size, development rate and fecundity of the moths to be reduced.
• 3 The resource quality had no effect on the mortality due to the virus. In contrast, sublethal effects of the virus on pupal weight were more apparent under conditions of resource limitation.
• 4 Considerable variation between the sublethal effects after challenge with different doses of the virus was found. The balance between deleterious sublethal effects of the virus and the selection of more robust individuals by the bioassays is proposed as a mechanism to explain this variation.
• 5 Implications for the dynamics of insect hosts and their pathogens are discussed.

     

Detection of gaps in sinusoids by frog auditory nerve fibers: importance in AM coding

Physiological studies were carried out in the frog (Rana pipiens pipiens) eighth nerve to determine: (i) whether the modulation rate or the silent gap was the salient feature that set the upper limit of time-locking to pulsed amplitude-modulated (PAM) stimuli, (ii) the gap detection capacity of individual eighth nerve fibers. Time-locked responses of 79 eighth nerve fibers to PAM stimuli (at the fiber's characteristic frequency) showed that the synchronization coefficient was a low-pass function of the modulation rate. In response to PAM stimuli having different pulse durations, a fiber gave rise to non-overlapping modulation transfer functions. The upper cut-off frequency of time locking was higher when tonepulses in PAM stimuli had shorter duration. The fact that the cut-off frequency was different for the different PAM series suggested that the AM rate was neither the sole, nor the main, determinant for the decay in time-locking at high AM rates. Gap detection capacity was determined for 69 eighth nerve fibers by assessing fiber's spiking activities to paired tone-pulses during an OFF-window and an ON-window. It was found that the minimum detectable gap of eighth nerve fibers ranged from 0.5 to 10 ms with an average of 1.23–2.16 ms depending on the duration of paired tone pulses. For each fiber, the minimum detectable gap was longer when the duration of tone pulses comprising the twin-pulse stimuli was more than four times longer. When the synchronization coefficient was plotted against the silent gap between tones pulses in the PAM stimuli, the gap response functions of a fiber as derived from multiple PAM series were equivalent to gap response functions deriving from twin-pulse series suggesting that it was the silent gap which primarily determined the upper limit of time-locking to PAM stimuli.Abbreviations MTF modulation transfer function - PAM pulse amplitude modulated - SAM sinusoidally amplitude modulated - SC synchronization coefficient - TW time window     

Bayesian signal extraction from noisy FT NMR spectra

Summary The statistical interpretation of the histogram representation of NMR spectra is described, leading to an estimation of the probability density function of the noise. The white-noise and Gaussian hypotheses are discussed, and a new estimator of the noise standard deviation is derived from the histogram strategy. The Bayesian approach to NMR signal detection is presented. This approach homogeneously combines prior knowledge, obtained from the histogram strategy, together with the posterior information resulting from the test of presence of a set of reference shapes in the neighbourhood of each data point. This scheme leads to a new strategy in the local detection of NMR signals in 2D and 3D spectra, which is illustrated by a complete peak-picking algorithm.     

Long-term changes in frequencies ofPythium iwayamai andP. paddicum in upland- and paddy-field soils

The long-term changes in the frequencies ofPythium iwayamai andP. paddicum in upland- and flooded paddy-field soils were compared. The frequencies of both species fell in both soils within the first 6 months after they had been buried. After 36 and 48 months,P. iwayamai showed higher frequency thanP. Paddicum in upland-field soil, whileP. paddicum showed higher frequency thanP. iwayamai in paddy-field soil. These findings indicate respectively higher colonization ability to organic matters ofP. iwayamai in upland-field soil andP. paddicum in paddy-field soil.This study was partly supported by a Grant-in-Aid (no. 63560048) from the Ministry of Education, Science and Culture, Japan.     

The Presence of (+)-S-Adenosyl-l-Methionine in the Rat Brain and Its Lack of Effect on Phenylethanolamine N-Methyltransferase Activity

Abstract: (+)-S-Adenosyl- l -methionine [(+)-SAM] was isolated from rat brain and was quantified by HPLC followed by UV spectrophotometric measurements and by ¹H-NMR. Its estimated ratio in brain is 3% of total SAM. Because of its commercial unavailability, (+)-SAM was also prepared from chemically synthesized SAM by separation of the two diastereoisomers on a preparative reverse-phase Nucleosil C8 column. The (+) diastereoisomer thus obtained was then assayed in vitro both as an inhibitor and a substrate of phenylethanolamine N -methyltransferase. Enzymatic activity was measured by HPLC analysis. It was shown that (+)-SAM has no effect on phenylethanolamine N -methyltransferase activity; therefore, it is unlikely that (+)-SAM plays any possible role in regulation of adrenaline synthesis in the brain.     

Object detection by honeybees: Why do they land on edges?

Behavioural experiments using a variety of experimental situations (Figs. 1, 3, 6, 7, 9) were conducted to investigate the visual cues which bees use in the task of object-ground discrimination. The bees' flight and landing behaviour was video-filmed throughout the experiments. The evaluation of the video data shows that bees trained to find a randomly textured figure raised above a similarly textured ground land mainly on the boundaries of the figure, facing its inner surface (Fig. 2a, b). Bees can also be trained to find a hole, i.e. a low texture viewed through a window cut in a raised texture, but these bees are not attracted to the edges of the hole (Fig. 5a, b). Bees trained to a single edge between a low and a raised random texture land at the edge mainly facing the raised side (Table 1). Bees approaching the edge from the high side cross the edge in most cases without landing on it (Table 1). Bees trained to an edge between 2 striped patterns, one raised above the other, again land on the edge facing the raised pattern, regardless of whether the stripes on the 2 patterns run parallel or perpendicular to each other or to the edge (Fig. 8). In this case, the bees acquire range information by flying in oblique directions with respect to the orientation of the stripes (Fig. 10). All of the results suggest that the edge elicits landings when the bee perceives a local increase in the speed of image motion, signalling an abrupt decrease in range. This is corroborated by the results of further experiments in which artificial motion was used to simulate range differences between the two sides of an edge (Table 2). We conclude that image speed is a powerful cue in range discrimination as well as object detection. Dedicated to G. Adrian Horridge on the occasion of his retirement     

Water conditions influence the detectability of Crossodactylus gaudichaudii (Anura,Hylodidae) in streams of the Atlantic Forest

Stream-dwelling amphibians' occurrence, behaviour and reproductive success are strongly influenced by dynamic abiotic factors, for example, water flow and spray. These factors can disproportionately affect these frogs due to their dependency on specific favourable conditions for development and incapacity to disperse from unfavourable environments. We analysed the influence of environmental covariates on the detectability of Crossodactylus gaudichaudii, an amphibian species endemic to streams in the Brazilian Atlantic Forest. We conducted sampling in the streams of the Duas Bocas Biological Reserve, Brazil, and we measured air and water temperature, air humidity and pH of water on each sampling occasion. We estimated the effects of variables on the detectability of the species using single-season occupancy models. Our results indicated that the detectability of the species increases on occasions with higher water temperatures (24–26°C) and lower pH (5.0–5.5). We investigated the influence of these covariates only on the detectability of adult frogs, but it is likely that the physiochemical properties of stream water are more important to aquatic larvae, and hence, the probability of their detection. Given this, further studies should examine the relevance of covariates on the detectability of adult frogs as well as larvae.     

Factors controlling the population dynamics of the clonal helophyte Ranunculus lingua

Abstract. Two marginal and two central populations of the pseudo-annual aquatic plant Ranunculus lingua were studied over four years. The main purpose was to quantify potentially influential abiotic and biotic factors and to derive predictions about life-history differences between the populations. Variation in abundance and height of R. lingua ramets at different depths were related to water-level fluctuations, to abundance of other helophyes (emergent macrophytes), and to the occurrence of invertebrate grazing and fungal pathogens. Clear differences between marginal and central populations were shown in the depth distribution of ramet numbers and ramet heights, as well as in the dynamic patterns, where marginal populations had a higher flux of ramets. These patterns and regression analyses indicated that abiotic factors have a greater influence in marginal populations, whereas biotic factors are more important in central populations. It is suggested that marginal habitats for R. lingua would favour life-histories with a high reproductive capacity, whereas a large size of ramet would be the most important life-history feature in central habitats. This was supported by the fact that ramets in marginal populations, in spite of their smaller size, produced higher number of rhizomes than ramets in central populations. Variation in regional abundance was finally related to differences in demographic processes and dispersal potential between the populations.