Simulium metallicum cytospecies E larval habitat characterization in the Altamira focus of onchocerciasis, northern Venezuela

Abstract. Simulium metallicum sibling species E was identified cytotaxonomically from an onchocerciasis focus at Altamira in northern Venezuela. S. metallicum E larvae were sampled monthly from two small mountain streams over a 15-month period (July 1990 to September 1991) and eleven habitat variables were measured at two altitudes. One stream consistently harboured much higher densities of S. metallicum E larvae than the other, with three annual peaks of abundance: during the dry season and at the beginning and end of the rainy season. These peak densities were correlated with high rainfall 4 months previously. Larvae were most abundant on submerged rocks and fallen leaves, in small shallow areas characterized by slow water current, high conductivity and sparse terrestrial vegetation cover. Stream variables which best explained the temporal changes in abundance were water discharge and conductivity. The population dynamics of S. metallicum E appeared to be influenced primarily by interactions between stream discharge and substrate stability. Relevance of these results to vector control with larvicides is discussed.     

Dynamics of root growth and decay in two grasses native to semi-arid Argentina

The pattern of root growth and decay in Stipa tenuis Phil, and Piptochaetium napostaense (Speg.) Hack, was examined under field conditions in root observation chambers. The roots of both species grew uninterruptedly throughout the whole year. Root elongation during spring, summer, and early autumn can be six and five times as high as that in the late autumn to winter period for S. tenuis and P. napostaense, respectively. Root decay was a continuous process in both species throughout the year, with maximum decay rates occurring from late spring through to the middle of autumn. Comparison of minimum and maximum values registered during the year showed a root decay ratio of about 4:1 for S. tenuis and one of 5:1 for P. napostaense. During the period of maximum root growth, both species showed a pulse-like pattern of root elongation in response to rapid changes in water availability. In a semi-arid region in which the soil is notably shallow, root growth behaviour of this kind should allow these species to respond opportunistically to water.     

Temperature control of male embryo viability of the aphid Megoura viciae

Summary

Early stages of gametogenesis were observed in embryos of Megoura viciae Buckton at two temperatures, 24°C and 27°C. The higher temperature is lethal for male embryos but not for female embryos. Spermatogenesis proceeds to the synizesis contraction stage at both temperatures but goes no further at 27°C. All the spermatocytes degenerate prior to undergoing metaphase I and gamete degeneration is followed by the death of the male embryos. In oogenesis, synizesis lasts for much longer and no differential viability at the two temperatures can be observed. A possible explanation, related to the different timing of meiosis in the two sexes, is proposed and discussed.     

3,4 Dichloroaniline-haemoglobin adducts in humans: preliminary data on agricultural workers exposed to propanil

Propanil is one of the major herbicides used on rice-paddies and is thought to produce adverse health effects through the action of its metabolite 3,4-dichloroaniline (3,4-DCA). T he feasibility of monitoring human exposure to propanil on the basis of 3,4-DCA adducts to haemoglobin (Hb) was investigated. We developed a method based on gas chromatography negative ion chemical ionization-mass spectrometry (NICI-GC-MS) to quantify 3,4-DCA released from human Hb after alkaline hydrolysis of the protein. 3,4-DCA-Hb adducts were identified in agricultural workers exposed to propanil and were detectable even 4 months after the last herbicide application. Urine samples collected at the same time had no measurable level of 3,4-DCA. 3,4-DCA-Hb adducts might be useful for monitoring human exposure to 3,4-DCA from agricultural sources.     

Induction of the Synthesis of Melanin and Pteridine in Cells Isolated from the Axolotl Embryo

It has previously been reported that when LiCl and tyrosine is added to ectodermal cells isolated from the blastula of Ambystoma mexicanum , then the synthesis of melanin is initiated in cells not normally engaged in this activity (mesenchyme cells, nerve cells and undifferentiated animal cells). In the present paper it has been shown that to obtain this effect tyrosine (0.02 mM) has to be present in the culture medium during at least one of the first seven days of culture, thus several days before melanin is produced. It is concluded that the added tyrosine is acting as an inductor of, and not as a substrate for the synthesis of melanin.
In the normal cultures it is possible to observe the spontaneous formation of yellow cells, indicating that they have produced pteridine. These cells are spherical, suggesting that they are undifferentiated embryonic cells. GTP is a precursor in the synthesis of pteridine, and in analogy with the observations made with tyrosine it was found that in the presence of LiCl a number of different cell types elaborate pteridine when GTP (0.1 mM) is added to the medium. Also in this case was it possible to show that GTP acts as an inductor, not as a substrate.     

Host‐associated genetic differentiation in a seed parasitic weevil Rhinusa antirrhini (Coleptera: Curculionidae) revealed by mitochondrial and nuclear sequence data

Plant feeding insects and the plants they feed upon represent an ecological association that is thought to be a key factor for the diversification of many plant feeding insects, through differential adaptation to different plant selective pressures. While a number of studies have investigated diversification of plant feeding insects above the species level, relatively less attention has been given to patterns of diversification within species, particularly those that also require plants for oviposition and subsequent larval development. In the case of plant feeding insects that also require plant tissues for the completion of their reproductive cycle through larval development, the divergent selective pressure not only acts on adults, but on the full life history of the insect. Here we focus attention on Rhinusa antirrhini (Curculionidae), a species of weevil broadly distributed across Europe that both feeds on, and oviposits and develops within, species of the plant genus Linaria (Plantaginaceae). Using a combination of mtDNA (COII) and nuclear DNA (EF1‐α) sequencing and copulation experiments we assess evidence for host associated genetic differentiation within R. antirrhini. We find substantial genetic variation within this species that is best explained by ecological specialisation on different host plant taxa. This genetic differentiation is most pronounced in the mtDNA marker, with patterns of genetic variation at the nuclear marker suggesting incomplete lineage sorting and/or gene flow between different host plant forms of R. antirrhini, whose origin is estimated to date to the mid‐Pliocene (3.77 Mya; 2.91–4.80 Mya).     

NEXT GENERATION HEALTHY SOUP: AN EXPLORATION USING CONJOINT ANALYSIS

This paper presents results on consumer attitudes towards healthy soup, using conjoint analysis, executed on the Internet. The results show moderate interest in new ideas for the total panel, but reveal three concept-response segments. The first segment responds to nutrition and functional ingredients. The second segment responds to packaging and convenience. The third segment responds to taste and ingredients. Statistical analysis confirms the idea that they represent different 'mind-sets'. The segmentation based on psychographic variables is a useful tool to identify the features of the next generation "healthy soups" and to design custom products on the basis of consumer requirements.     

3,4 Dichloroaniline-haemoglobin adducts in humans: preliminary data on agricultural workers exposed to propanil

Propanil is one of the major herbicides used on rice-paddies and is thought to produce adverse health effects through the action of its metabolite 3,4-dichloroaniline (3,4-DCA). T he feasibility of monitoring human exposure to propanil on the basis of 3,4-DCA adducts to haemoglobin (Hb) was investigated. We developed a method based on gas chromatography negative ion chemical ionization-mass spectrometry (NICI-GC-MS) to quantify 3,4-DCA released from human Hb after alkaline hydrolysis of the protein. 3,4-DCA-Hb adducts were identified in agricultural workers exposed to propanil and were detectable even 4 months after the last herbicide application. Urine samples collected at the same time had no measurable level of 3,4-DCA. 3,4-DCA-Hb adducts might be useful for monitoring human exposure to 3,4-DCA from agricultural sources.     

Development of the leafy shoot in Sphagnum (Bryophyta) involves the activity of both apical and subapical meristems

This light- and electron-microscope study of four species of Sphagnum reveals that stem elongation involves meristematic activities unique to the group and hitherto unrecognized. The internal tissue of the mature stem arises by the concerted activity of an apical (primary) and a subapical (secondary) meristem. The primary meristem comprises the immediate derivatives of the single apical cell. Following a small number of divisions, the primary derivatives differentiate into highly vacuolate parenchymatous cells with a storied arrangement. Subsequently, the large vacuoles are replaced by numerous small vacuoles and the cells then divide repeatedly, by transverse septa, producing files of about nine short cells. Finally, ninefold elongation of these secondary cells is responsible for extension growth of the main stem below the mature capitulum. An early step in primary differentiation is the confinement of pre-existing plasmodesmata to distinct pitted areas. Further enlargement of the cells during primary and secondary differentiation involves the thickening of non-pitted wall areas, followed by expansion and thinning out, while the pitted areas remain virtually unchanged. A cortical array of microtubules is regularly found in association with non-pitted wall areas, while the unexpanded pitted areas are associated with smooth endoplasmic reticulum showing continuity with desmotubules. Though sharing much the same cytology as the conducting cells in bryoid mosses, in terms of their development the central stem cells in Sphagnum are not homologous with those of other mosses. The unique mode of stem development may be an important factor in the ecological success of Sphagnum .