Mechanical stress and reactivity in organic solids

Organic single crystals provide an ideal model for studying the factors that influence chemical processes in structured media. Reaction trajectories are well defined and reveal the influence of spontaneous mechanical stresses equivalent to tens of thousands of atmospheres. Analysis of molecular and crystal structures helps to explain both local mechanical properties, which influence reactions, and bulk properties such as melting point, compressibility, and surface energy.     

Genetic structure of human populations

We studied human population structure using genotypes at 377 autosomal microsatellite loci in 1056 individuals from 52 populations. Within-population differences among individuals account for 93 to 95% of genetic variation; differences among major groups constitute only 3 to 5%. Nevertheless, without using prior information about the origins of individuals, we identified six main genetic clusters, five of which correspond to major geographic regions, and subclusters that often correspond to individual populations. General agreement of genetic and predefined populations suggests that self-reported ancestry can facilitate assessments of epidemiological risks but does not obviate the need to use genetic information in genetic association studies.     

Complex multicolor tilings and critical phenomena in tetraphilic liquid crystals

T-shaped molecules with a rod-like aromatic core and a flexible side chain form liquid crystal honeycombs with aromatic cell walls and a cell interior filled with the side chains. Here, we show how the addition of a second chain, incompatible with the first (X-shaped molecules), can form honeycombs with highly complex tiling patterns, with cells of up to five different compositions ("colors") and polygonal shapes. The complexity is caused by the inability of the side chains to separate cleanly because of geometric frustration. Furthermore, a thermoreversible transition was observed between a multicolor (phase-separated) and a single-color (mixed) honeycomb phase. This is analogous to the Curie transition in simple and frustrated ferro- and antiferromagnets; here spin flips are replaced by 180° reorientations of the molecules.     

Impact of soil stockpiling and mining rehabilitation on earthworm communities

As key ‘ecosystem engineers’, earthworms improve mineralization of organic matter, plant growth, soil quality, and are an important component of many terrestrial food webs. Under appropriate conditions, they are therefore likely to accelerate the restoration of soil ecosystem function after mining.Conserving naturally occurring populations and facilitating their recolonisation appears as the most efficient way to increase earthworms’ overall effect. The impact of mining activities and restoration measures on New Zealand endemic earthworm communities was tested. Earthworm biomass and diversity were compared in four different habitat types.Mining activities, not surprisingly, are shown here to have a detrimental impact on earthworm communities. Soil stockpiling induces anaerobic conditions at and below a depth of 1 m, where earthworms do not survive. The use of stockpiled soil for vegetation replanting therefore leads to low diversity and low abundance of earthworms. An alternative restoration technique consisting in transferring vegetation and soil units (the vegetation direct transfer) was efficient in preserving earthworm populations with earthworm biomass and diversity not significantly different from those observed in undisturbed areas. Based on these results, we recommend vegetation direct transfer (VDT) to be prioritised whenever it is logistically and economically feasible. When VDT is not applicable, low stockpiles should be prioritised as they will comprise a higher proportion of good quality soil (at the surface) and a lower proportion of anaerobic and compacted soil (below 1 m depth at the studied site).     

Insecticide resistance status of Aedes aegypti (L.) from Colombia

BACKGROUND: To evaluate the insecticide susceptibility status of Aedes aegypti (L.) in Colombia, and as part of the National Network of Insecticide Resistance Surveillance, 12 mosquito populations were assessed for resistance to pyrethroids, organophosphates and DDT. Bioassays were performed using WHO and CDC methodologies. The underlying resistance mechanisms were investigated through biochemical assays and RT‐PCR. RESULTS: All mosquito populations were susceptible to malathion, deltamethrin and cyfluthrin, and highly resistant to DDT and etofenprox. Resistance to lambda‐cyhalothrin, permethrin and fenitrothion ranged from moderate to high in some populations from Chocó and Putumayo states. In Antioquia state, the Santa Fe population was resistant to fenitrothion. Biochemical assays showed high levels of both cytochrome P450 monooxygenases (CYP) and non‐specific esterases (NSE) in some of the fenitrothion‐ and pyrethroid‐resistant populations. All populations showed high levels of glutathione‐S‐transferase (GST) activity. GSTe2 gene was found overexpressed in DDT‐resistant populations compared with Rockefeller susceptible strain. CONCLUSIONS: Differences in insecticide resistance status were observed between insecticides and localities. Although the biochemical assay results suggest that CYP and NSE could play an important role in the pyrethroid and fenitrothion resistance detected, other mechanisms remain to be investigated, including knockdown resistance. Resistance to DDT was high in all populations, and GST activity is probably the main enzymatic mechanism associated with this resistance. The results of this study provide baseline data on insecticide resistance in Colombian A. aegypti populations, and will allow comparison of changes in susceptibility status in this vector over time. Copyright © 2011 Society of Chemical Industry     

A rapid and simple method for determining fungicide resistance in Botrytis

A simple test based on the germination of conidia of Botrytis on agar media augmented with various fungicides has been developed. Average concentrations causing a 50% reduction of germ-tube growth (EC₅₀) of highly sensitive isolates were determined on 1% malt extract agar (thiophanate-methyl 0.090 ppm; iprodione 0.566 ppm; fludioxonil 0.026 ppm; fenhexamid 0.144 ppm), 1% malt extract agar with 100 ppm salicyl hydroxamic acid (QoI fungicides, viz. trifloxystrobin 0.009 ppm; pyraclostrobin 0.013 ppm; azoxystrobin 0.087 ppm), 0.5% yeast extract agar (boscalid 0.069 ppm) and 0.5% sucrose agar (cyprodinil 0.053 ppm). In order to detect different levels of resistance against these various fungicides, two discriminatory concentrations were identified for each compound. A routine assay method was developed in which drops of a conidial suspension harvested directly from diseased plant material or sporulating cultures were incubated on each of 20 different agar media. Because of a very short time-span of 24–48 h between sample collection and evaluation of results, field-specific information on the occurrence, frequency and types of resistance of Botrytis against common botryticides in soft-fruit production may be generated prior to the main fungicide spray season at blossom time.

     

Effects of grazing practices and fossorial rodents on a winter avian community in Chihuahua, Mexico

Chihuahuan Desert grasslands are important wintering grounds for grassland and shrub-adapted birds. Many species belonging to these assemblages are currently exhibiting population declines. One area recognized for its importance to biological diversity, including grassland birds, is the Janos-Nuevo Casas Grandes black-tailed prairie dog (Cynomys ludovicianus) complex in northwestern Chihuahua, Mexico, an area containing 58 colonies with 30,000 ha of prairie dogs. This is one of the largest remaining prairie dog complexes and the only intact complex in the Chihuahuan Desert. In its current condition, a large percentage of this complex is of reduced value to wildlife. Overgrazing on communal (ejido) lands has resulted in areas being comprised of annual grasses and forbs. The density of active prairie dog burrows and banner-tailed kangaroo rat (Dipodomys spectabilis) mounds as well as avian diversity and abundance were lower on ejido lands than an adjacent private ranchland with and without prairie dogs. Few avian species used overgrazed portions of the prairie dog colony. Community similarity among plot types was low due to different management practices and differences on and off colony. To retain, and in many instances restore the biological diversity of this important region it is essential to work with local ejidos on grazing management.     

Development of an analytical scheme for simazine and 2,4-D in soil and water runoff from ornamental plant nursery plots

The transport and fate of pesticides applied to ornamental plant nursery crops are not well documented. Methodology for analysis of soil and water runoff samples concomitantly containing the herbicides simazine (1-chloro-4,6-bis(ethylamino)-s-triazine) and 2,4-D ((2,4-dichlorophenoxy)acetic acid) was developed in this research to investigate the potential for runoff and leaching from ornamental nursery plots. Solid-phase extraction was used prior to analysis by gas chromatography and liquid chromatography. Chromatographic results were compared with determination by enzyme-linked immunoassay analysis. The significant analytical contributions of this research include (1) the development of a scheme using chromatographic mode sequencing for the fractionation of simazine and 2,4-D, (2) optimization of the homogeneous derivatization of 2,4-D using the methylating agent boron trifluoride in methanol as an alternative to in situ generation of diazomethane, and (3) the practical application of these techniques to field samples.     

Microbial activities in a histosol: Effects of wood ash and NPK fertilizers

Mineralization of organic matter and microbial activities in an intensively cultivated acid, N-rich peat soil planted with Salix sp. cv. aquatica were examined for 3 yr. The soil was amended with wood ash or NPK fertilizers providing N as ammonium nitrate or urea. The wood ash amendment (10 tons ha^?1) increased soil pH from 4.6 to 5.5 and increased markedly all microbial activities measured, resulting in increased mineralization and N availability, and in loss of 9% total soil N during the first year. The addition of ammonium nitrate caused a corresponding though less pronounced increase in N mineralization. Cellulose decomposition increased in all amended soils, reaching rates 53–86% higher than in non-amended soil. Potential N₂ fixation (C₂H₂ reduction) by free-living organisms was increased by the ash-amendment. Potential denitrification rates were positively correlated (r = 0.98) with the presence of water-soluble organic-C, which was more abundant in ash-amended and non-amended soils than in the soils fertilized with N.