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Based on the knowledge that alpaca (Lama pacos) have a lower fractional outflow rate of feed particles (particulate FOR) from their forestomach than sheep (San Martin 1987), the current study measured methane (CH4) production and other digestion parameters in these species in three successive experiments (1, 2 and 3): Experiment 1, lucerne hay fed indoors; Experiment 2, grazed on perennial ryegrass/white clover pasture (PRG/WC); and Experiment 3, grazed on birdsfoot trefoil (Lotus corniculatus) pasture (Lotus). Six male alpaca and six castrated Romney sheep were simultaneously and successively fed on the forages either ad libitum or at generous herbage allowances (grazing). CH4 production (g/day) (using the sulphur hexafluoride tracer technique), voluntary feed intake (VFI), diet quality, and protozoa counts and volatile fatty acid concentrations in samples of forestomach contents were determined. In addition, feed digestibility, energy and nitrogen (N) balances and microbial N supply from the forestomach (using purine derivatives excretion) were measured in Experiment 1.Diets selected by alpaca were of lower quality than those selected by sheep, and the voluntary gross energy intakes (GEI, MJ) per kg of liveweight0·75 were consistently lower (Pv. 1·36, 0·61 v. 1·32 and 0·77 v. 2·53 on lucerne hay, PRG/WC and Lotus, respectively). Alpaca and sheep did not differ (P>0·05) in their CH4 yields (% GEI) when fed on lucerne hay (5·1 v. 4·7), but alpaca had a higher CH4 yield when fed on PRG/WC (9·4 v. 7·5, Pv. 2·7, PPP>0·05) in diet N partition or microbial N yield, but alpaca had higher (Pv. 0·461) and lower (Pv. 5·8 % GEI) than sheep. It is suggested that differences between these species in forestomach particulate FOR might have been the underlying physiological mechanism responsible for the differences in CH4 yield, although the between-species differences in VFI and diet quality also had a major effect on it.

Effects of five weed management regimes on abundance of weeds, insect pests, generalist predators and on pest damage and rice yield were investigated in upland rice in Côte d‘Ivoire over two years. In both years there was a highly significant negative correlation between weed biomass and grain yield across all treatments. Only two pest insect groups,Nephotettixspp. (Cicadellidae) and seed sucking Heteroptera, were consistently more abundant in unweeded plots and had a consistent significant positive correlation between abundance and weed biomass across all seven treatments. These polyphagous groups may have been more dependent on resources provided by weeds than the other pests studied. However, pest damage was not affected by presence or absence of weeds, suggesting that populations were below a damage threshold. Ants were the most abundant predators in the rice canopy and were most abundant in unweeded treatments. Abundance of both ants and spiders was significantly positively correlated with weed biomass across treatments. Abundance of reduviid bugs was positively correlated with weed biomass only in 1995. Any benefits due to presence of weeds in the crop were completely outweighed by loss of crop yield due to weed competition. However, if crop losses due to weeds were sufficiently reduced, it is possible that significant losses due to insect pests might emerge.

SUMMARYAgronomic research was carried out on upland rice in Toledo District, Belize, in 1979–86, with the objective of improving returns from the traditional system of shifting cultivation and of examining the potential for reducing the demand for new land by cropping for more than one season. The rice was grown in the wet season on land cleared from forest by slash and burn, using a traditional planting technique, placing seed in holes made with a pointed stick.In a series of fertilizer experiments, in which rice was grown for up to 7 consecutive years, urea and triple superphosphate both increased grain yield, whereas muriate of potash had no effect. Mean yield in the fifth year was 85 % of that in the first. Urea and triple superphosphate both increased the number of full grains/panicle.A slash and mulch weed control treatment before sowing resulted in low yields of grain in the third year; yield after the use of propanil and 2,4-D (after sowing) was, on average, 77% of the yield after hand weeding; omitting weed control after sowing led to very low yields, particularly in the second and third years.In the varieties Bluebonnet and C22, grain yield was increased by reducing the distance between stations, particularly where 6, rather than 15, seeds were sown per station. Reducing the distance between stations increased the leaf area index during crop development and the number of panicles/m2, which more than counterbalanced reductions in the number and area of leaf blades per plant, the number of panicles per plant and the number of full grains per panicle. However, the yield/kg of seed sown and per hour spent planting was greatest at the widest spacing. C22 produced more panicles per plant and a greater weight of grain per plant and per hectare than Bluebonnet.It was concluded that returns from the traditional system can be improved and the demand for new land reduced.

Microprobe analysis of biological tissue is now in the end phase of transition from instrumental and technique development to applications pertinent to questions of physiological relevance. The promise,implicit in early investigative efforts, is being fulfilled to an extent much greater than many had predicted. It would thus seem appropriate to briefly report studies exemplifying this, ∿. In general, the distributions of ions in tissue in a preselected physiological state produced by variations in the external environment is of importance in elucidating the mechanisms of exchange and regulation of these ions.

Elemental analysis by means of energy loss electrons transmitted through thin specimens has the potential of being a very useful technique for the microanalysis of light elements (e.g. 1-5). The advantages of the energy loss technique over x-ray detection have been discussed in detail in ref. 1. They are basically, the lack of dependence of the detection efficiency on the fluorescent yield (which decreases rapidly with decreasing Z) and the possibility of increased collection efficiency of the energy loss electrons (which are concentrated at relatively small angles with respect to the incident beam direction).

Toxic organic mercury compounds, especially methyl mercury (MeHg), have been responsible for severe environmental contamination. Industrial effluents of inorganic or metallic mercury are methylated by aquatic organisms leading to transfer and bioconcentration of MeHg up the food chain to fish and man. In vivo mammalian and teleostean (bony fish) models have provided useful data on mercury toxicity; cultures of animal cells have been used to investigate the toxic actions of heavy metals such as mercury. The present study was designed to determine if RTG-2 cells, a fibroblast-like line derived from rainbow trout (Salmo gairdneri) gonads, would provide a highly controlled system in which to study the mercury-cell interaction. A mammalian cell line derived from Chinese hamster ovary (CHO)2 and known to be sensitive to MeHg3 was chosen as a positive control. The specific objective was to determine the effect of MeHg on RTG-2 and CHO cell viability and ultrastructure.

The use of electron energy loss spectroscopy (ELS) for elemental analysis of thin films holds considerable promise. This technique has definite advantages in comparison with energy dispersive X-ray spectroscopy (EDS) for two fundamental reasons. First, the detection sensitivity is independent of the fluorescence yield, since for each inner shell excitation an energy loss electron exists as opposed to only a finite probability that an excitation will result in a X-ray emitted. Second, the information carrying energy loss electrons are contained in a small solid angle about 0° scattering angle as opposed to the resulting X-rays which are emitted uniformly over 4Π steradians. This means that a large fraction of the energy loss electrons can be detected (up to ∼90%) compared to only a small fraction (∼1%) of the emitted X-rays with an EDS system.

The advantages of parallel detection systems for energy loss spectometry are certainly clear. A variety of approaches are possible ranging from simple film recording to elaborate intensified television cameras. We are in the process of evaluating one approach to such a parallel detection system, which consists of; a magnetic post-spectrometer lens to increase dispersion, a phosphor conversion plate, glass coupling lenses, a dual channeltron image intensifier, and a cooled photodiode array (Reticon RL256C/17). A schematic diagram of the system is shown in Fig. 1.The post-spectrometer lens is an RCA-3G intermediate lens which typically magnifies (∼15x) the dispersion to ∼25μm/ev with a rotation of ∼90°. Although the dispersion plane of the straight edge sector magnet used is tilted at 30° from the beam axis, pre-spectrometer optics reduce the angular divergence of the beam entering and leaving the spectrometer to ∼1 mr and the consequently large depth of focus assures that the dispersed beam is in focus across the conversion plate, perpendicular to the beam axis.

The toxicity of mercury and its compounds is widely recognized. Symptoms of mercury intoxication vary greatly depending on mode of entry, form of mercury, dose, and duration of exposure. In humans, the principal toxic effects of inorganic mercury involve the liver and kidney. Organic mercurials such as methylmercury have a more pronounced effect on the central nervous system.Pharmacological studies suggest an intestinal elimination of organic mercurials and the possibility of an intestinal lesion associated with mercury. Autoradiographic studies have indicated that uptake of 203HgCl2 by rat paneth cells exceeded that of other cells of the small intestine. Paneth cells line the bottoms of intestinal crypts. They are pyramidal in shape with basally located nuclei and large secretory granules in their apical aspect which contain the bacteriolytic enzyme lysozyme.

The purpose of this symposium/tutorial presentation will be to assess the current state and future prospects of both energy dispersive x-ray analysis and electron energy loss analysis in the submicron spectroscopy of biological systems.In the successful use of any analytical technique in a biological study, the specimen preparative steps are crucial to the ultimate validity of the results. Nowhere is this more true, than in the analytical electron microscope. Fortunately, current techniques of cryofixation, cryosectioning and analysis, including freeze drying, have developed such that morphology and elemental distributions are typically preserved to a spatial resolution at least as good as the analytical and electron optical instrumentation allow.

Electron microprobe analysis has been used increasingly in, recent years for low Z analysis of thin biological sections. Although this technique has produced useful results, the sensitivity is limited by two main factors. First, the fluorescence yield (wK) decreases rapidly with decreasing Z. Using the value of wK (for carbon for example, only about one out of every 400 K ionizations in carbon results in a carbon x-ray. Second, this poor x-ray production efficiency is coupled with the inherently poor x-ray collection efficiency of most microprobe detectors. In thin sections the x-rays are emitted uniformly over 4TT steradians but the detector subtends only a small solid angle at the specimen. Hall estimates the collection efficiency of most diffracting detectors at 10−4 and, with the qualification of much lower peak to background ratios, he estimates the collection efficiency of solid state nondiffractive detectors as 10−4 to 10−2.