Use of a hydrological model for environmental management of the Usangu Wetlands, Tanzania

Wetlands / Rivers / Ecology / Environmental effects / Remote sensing / Hydrology / Simulation models / Water budget / Irrigated sites / Land cover / Time series analysis / Tanzania / Usangu Wetlands / Great Ruaha River

Assessment of trace metal contamination by geochemical normalisation in sediments of two lagoons: A comparative study of the Kpeshie and Muni lagoons, Ghana

Heavy metal contamination status of bottom sediments of two lagoons was compared by the employment of Enrichment Factor (EF) analysis for Iron (Fe), Manganese (Mn), Cupper (Cu), Lead (Pb), Chromium (Cr), Nickel (Ni), Silver (Ag), Zinc (Zn) and Mercury (Hg). Kpeshie Lagoon recorded enrichment (EF ≥ 1) for Cd, Pb, Ag, Hg and Zn, whilst Muni Lagoon recorded enrichment for Cd, Mn, Ag, Hg and Zn as metals of anthropogenic influence. Kpeshie, situated in a highly urbanized area, has 75% spatial distribution of Pb enrichment. The assessment shows that Ag and Hg are the most enriched metals in the sediments of both Lagoons, reaching extremely severe levels. Only Mn showed statistically significant difference in mean concentration of metals for both Lagoons. Pearson correlation matrix indicated that Pb had a strong relation with Ag, Hg and Zn (r = 0.956; p < 0.05) which is significant in Kpeshie. It also had a strong association with Ag and Hg but not with Zn (r = 0.240) in the Muni. The study clearly delineates Pb as a pollutant that designates the urban status of Kpeshie. Its associated metals; Ag, Hg and Zn which may be coming from a common source are from industrialized zones

Evaluation of four local plant species for insecticidal activity against Sitophilus zeamais Motsch. (Coleoptera: Curculionidae) and Callosobruchus maculatus (F) (Coleoptera: Bruchidae)

The study investigated the insecticidal properties of four local medicinal plants–Ricinus communis Linn. (castor bean), Jatropha curcas Linn. (coral/purging nut), Anacardium occidentale Linn. (cashew nut), and Erythrophleum sauvelens (sasswood)–under laboratory conditions against two storage pests, Sitophilus zeamais (Motsch.) and Callosobruchus maculatus (F.), using two methods of treatment, topical application of crude powder water extracts and dried powder admixture in grains. The materials were tested at 0, 1, 5, 10, and 20 per cent concentrations. Contact toxicity, repellence, and inhibition of progeny emergence were monitored after treatments. At 20 per cent, Ricinus showed the highest repellence of C. maculatus (96.08%), followed by Jatropha (68.15%), Anacardium (62.30%) and Erythrophleum (25.40%), respectively. Against S. zeamais, Anacardium recorded 80.32 per cent repellence, followed by Ricinus (60%), Jatropha (58%) and Erythrophleum (10.02%). At lower concentrations (1, 5 and 10%), repellence of all the plant extracts did not seem to follow any trend. Dried ground seeds or powder water extract of the four plant materials at a dose of 5 per cent (w/w) significantly reduced progeny emergence in treated maize and cowpea grains. From the study, R. communis seems to be the best candidate among the four plant species tested. It is highly toxic, repellent, and inhibits progeny emergence to a larger extent than the other three plants. Jatropha curcas and A. occidentale were also very effective. It is, therefore, concluded that R. communis, J. curcas, and A. occidentale have great potential to develop into botanical pesticides and must be exploited.). Les propriétés insecticides de quatre plantes médicinales locales: Ricinus communis Linn. (haricot de ricin), Jatropha curcas Linn. (noix de purge/corail), Anacardium occidentale Linn. (noix de cajou), et Erythrophleum sauveolens (le mançone) étaient étudiées sous les conditions de laboratoire contre deux ravageurs de stockage: Sitophilus zeamais (Motsch.) et Callosobruchus maculatus (F.) en utilisant deux méthodes de traitement: application actuelle d'extraits de poudre brute en eau et la poudre sèche additionnée engrains. Les matières étaient mises á l'essai à 0, 1, 5, 10, et 20% de concentrations. Toxicité par contact, repoussement et l'inhibition de l'émergence de progéniture étaient suivies de près après les traitements. A 20%, Ricinus montrait le repoussement le plus élevé de C. maculatus (96.08%), suivi par Jatropha (68.15%), Anacardium (62.30%) et Erythrophleum (25.40%), respectivement. Contre S. zeamais, Anacardium donnait 80.32% de repoussement, suivi par Ricinus (60%), Jatropha (58%), et Erythrophleum (10.2%). Aux concentrations plus faibles de (1, 5 et 10%), le repoussement de tous les extraits de plantes ne donnaient pas l'impression de suivre aucune tendance. Les grains secs moulus ou l'extrait de poudre en eau des quatre matières de plantes à une dose de 5% (w/w) causaient des réductions considérables dans l'émergence de progéniture de grains de maïs et de dolique traités. D'aprè l'étude, R. communis semble être le meilleur spécimen de quatre espèces de plantes mises à l'essai. Elle est hautement toxique, repoussante et inhibe l'émergence de progéniture dans une plus grande mesure que les trois autres plantes. Jatropha curcas et A. occidentale étaient également très efficace. Donc, la conclusion est tirée que R. communis, J. curcas et A. occidentale ont beaucoup de potentiel pour le développement en pesticides botaniques et devraient être exploité. Ghana Journal of Agricultural Science Vol. 39 (2) 2006: pp. 147-15

Spatial Variability of Trace Metals in Surface and Groundwater Within a Contaminated Mining Environment in Ghana

Abstract: The aim of the study was to spatially assess the distribution of heavy metals within the catchment of the Tarkwa mining area using interpolation techniques in a geographical information systems environment. Water quality trends for 84 sites in Tarkwa, a mining district in Ghana, were examined for fourtee

Thienoisoindigo-Based Semiconductor Nanowires Assembled with 2-Bromobenzaldehyde via Both Halogen and Chalcogen Bonding

We fabricated nanowires of a conjugated oligomer and applied them to organic field-effect transistors (OFETs). The supramolecular assemblies of a thienoisoindigo-based small molecular organic semiconductor (TIIG-Bz) were prepared by co-precipitation with 2-bromobenzaldehyde (2-BBA) via a combination of halogen bonding (XB) between the bromide in 2-BBA and electron-donor groups in TIIG-Bz, and chalcogen bonding (CB) between the aldehyde in 2-BBA and sulfur in TIIG-Bz. It was found that 2-BBA could be incorporated into the conjugated planes of TIIG-Bz via XB and CB pairs, thereby increasing the pi - pi stacking area between the conjugated planes. As a result, the driving force for one-dimensional growth of the supramolecular assemblies via pi - pi stacking was significantly enhanced. TIIG-Bz/2-BBA nanowires were used to fabricate OFETs, showing significantly enhanced charge transfer mobility compared to OFETs based on pure TIIG-Bz thin films and nanowires, which demonstrates the benefit of nanowire fabrication using 2-BB

Impact of urban agriculture on malaria vectors in Accra, Ghana

To investigate the impact of urban agriculture on malaria transmission risk in urban Accra larval and adult stage mosquito surveys, were performed. Local transmission was implicated as Anopheles spp. were found breeding and infected Anopheles mosquitoes were found resting in houses in the study sites. The predominant Anopheles species was Anopheles gambiae s.s.. The relative proportion of molecular forms within a subset of specimens was 86% S-form and 14% M-form. Anopheles spp. and Culex quinquefasciatus outdoor biting rates were respectively three and four times higher in areas around agricultural sites (UA) than in areas far from agriculture (U). The annual Entomological Inoculation Rate (EIR), the number of infectious bites received per individual per year, was 19.2 and 6.6 in UA and U sites, respectively. Breeding sites were highly transitory in nature, which poses a challenge for larval control in this setting. The data also suggest that the epidemiological importance of urban agricultural areas may be the provision of resting sites for adults rather than an increased number of larval habitats. Host-seeking activity peaked between 2–3 am, indicating that insecticide-treated bednets should be an effective control method

Molecular Ecology of Pyrethroid Knockdown Resistance in Culex pipiens pallens Mosquitoes

Pyrethroid insecticides have been extensively used in China and worldwide for public health pest control. Accurate resistance monitoring is essential to guide the rational use of insecticides and resistance management. Here we examined the nucleotide diversity of the para-sodium channel gene, which confers knockdown resistance (kdr) in Culex pipiens pallens mosquitoes in China. The sequence analysis of the para-sodium channel gene identified L1014F and L1014S mutations. We developed and validated allele-specific PCR and the real-time TaqMan methods for resistance diagnosis. The real-time TaqMan method is more superior to the allele-specific PCR method as evidenced by higher amplification rate and better sensitivity and specificity. Significant positive correlation between kdr allele frequency and bioassay-based resistance phenotype demonstrates that the frequency of L1014F and L1014S mutations in the kdr gene can be used as a molecular marker for deltamethrin resistance monitoring in natural Cx. pipiens pallens populations in the East China region. The laboratory selection experiment found that L1014F mutation frequency, but not L1014S mutation, responded to deltamethrin selection, suggesting that the L1014F mutation is the key mutation conferring resistance to deltamethrin. High L1014F mutation frequency detected in six populations of Cx. pipens pallens suggests high prevalence of pyrethroid resistance in Eastern China, calling for further surveys to map the resistance in China and for investigating alternative mosquito control strategies

Multiple Origins of Knockdown Resistance Mutations in the Afrotropical Mosquito Vector Anopheles gambiae

How often insecticide resistance mutations arise in natural insect populations is a fundamental question for understanding the evolution of resistance and also for modeling its spread. Moreover, the development of resistance is regarded as a favored model to study the molecular evolution of adaptive traits. In the malaria vector Anopheles gambiae two point mutations (L1014F and L1014S) in the voltage-gated sodium channel gene, that confer knockdown resistance (kdr) to DDT and pyrethroid insecticides, have been described. In order to determine whether resistance alleles result from single or multiple mutation events, genotyping of the kdr locus and partial sequencing of the upstream intron-1 was performed on a total of 288 A. gambiae S-form collected from 28 localities in 15 countries. Knockdown resistance alleles were found to be widespread in West Africa with co-occurrence of both 1014S and 1014F in West-Central localities. Differences in intron-1 haplotype composition suggest that kdr alleles may have arisen from at least four independent mutation events. Neutrality tests provided evidence for a selective sweep acting on this genomic region, particularly in West Africa. The frequency and distribution of these kdr haplotypes varied geographically, being influenced by an interplay between different mutational occurrences, gene flow and local selection. This has important practical implications for the management and sustainability of malaria vector control programs

Resistance to pirimiphos-methyl in West African Anopheles is spreading via duplication and introgression of the Ace1 locus

Vector population control using insecticides is a key element of current strategies to prevent malaria transmission in Africa. The introduction of effective insecticides, such as the organophosphate pirimiphos-methyl, is essential to overcome the recurrent emergence of resistance driven by the highly diverse Anopheles genomes. Here, we use a population genomic approach to investigate the basis of pirimiphos-methyl resistance in the major malaria vectors Anopheles gambiae and A. coluzzii. A combination of copy number variation and a single non-synonymous substitution in the acetylcholinesterase gene, Ace1, provides the key resistance diagnostic in an A. coluzzii population from Coˆte d’Ivoire that we used for sequence-based association mapping, with replication in other West African populations. The Ace1 substitution and duplications occur on a unique resistance haplotype that evolved in A. gambiae and introgressed into A. coluzzii, and is now common in West Africa primarily due to selection imposed by other organophosphate or carbamate insecticides. Our findings highlight the predictive value of this complex resistance haplotype for phenotypic resistance and clarify its evolutionary history, providing tools to for molecular surveillance of the current and future effectiveness of pirimiphos-methyl based interventions

Dynamics of insecticide resistance in malaria vectors in Benin: first evidence of the presence of L1014S kdr mutation in Anopheles gambiae from West Africa

<p>Abstract</p> <p>Background</p> <p>Insecticide resistance monitoring is essential to help national programmers to implement more effective and sustainable malaria control strategies in endemic countries. This study reported the spatial and seasonal variations of insecticide resistance in malaria vectors in Benin, West Africa.</p> <p>Methods</p> <p><it>Anopheles gambiae s.l </it>populations were collected from October 2008 to June 2010 in four sites selected on the basis of different use of insecticides and environment. WHO susceptibility tests were carried out to detect resistance to DDT, fenitrothion, bendiocarb, permethrin and deltamethrin. The synergist piperonyl butoxide was used to assess the role of non-target site mechanisms in pyrethroid resistance. <it>Anopheles gambiae </it>mosquitoes were identified to species and to molecular M and S forms using PCR techniques. Molecular and biochemical assays were carried out to determine <it>kdr </it>and <it>Ace.1^R</it>allelic frequencies and activity of the detoxification enzymes.</p> <p>Results</p> <p>Throughout the surveys very high levels of mortality to bendiocarb and fenitrothion were observed in <it>An. gambiae s.l</it>. populations. However, high frequencies of resistance to DDT and pyrethroids were seen in both M and S form of <it>An. gambiae s.s</it>. and <it>Anopheles arabiensis</it>. PBO increased the toxicity of permethrin and restored almost full susceptibility to deltamethrin. <it>Anopheles gambiae s.l</it>. mosquitoes from Cotonou and Malanville showed higher oxidase activity compared to the Kisumu susceptible strain in 2009, whereas the esterase activity was higher in the mosquitoes from Bohicon in both 2008 and 2009. A high frequency of <it>1014F kdr </it>allele was initially showed in <it>An. gambiae </it>from Cotonou and Tori-Bossito whereas it increased in mosquitoes from Bohicon and Malanville during the second year. For the first time the <it>L1014S kdr </it>mutation was found in <it>An. arabiensis </it>in Benin. The <it>ace.1^R</it>mutation was almost absent <it>in An. gambiae s.l</it>.</p> <p>Conclusion</p> <p>Pyrethroid and DDT resistance is widespread in malaria vector in Benin and both metabolic and target site resistance are implicated. Resistance was not correlated with a change of malaria species and/or molecular forms. The <it>1014S kdr </it>allele was first identified in wild population of <it>An. arabiensis </it>hence confirming the expansion of pyrethroid resistance alleles in Africa.</p