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      Efectos ovicida y larvicida del spinosad en Aedes aegypti (Diptera: Culicidae) Translated title: Ovicidal and larvicidal effects of spinosad in Aedes aegypti (Diptera: Culicidae)

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          Abstract

          Se evaluaron los efectos ovicida y larvicida del spinosad (Tracer 480SC) en Aedes aegypti a concentraciones de 0,1, 5 y 10ppm, a diferentes tiempos de exposición en condiciones controladas de temperatura (25±1ºC). En el primer experimento se observó un efecto ovicida bajo (promedio 6,6-8,2% de no eclosión y periodos de 12 a 96h de exposición) y en el segundo un efecto mediano (promedio 27,9-31,9% de no eclosión expuestos a spinosad de 1 a 12 semanas). La mortalidad de larvas se incrementó significativamente a mayor concentración de spinosad (100% a 10ppm a 6h) y a mayor tiempo de exposición (99,9% a 1ppm a 12h). Este bioinsecticida puede ser una buena herramienta para el control de inmaduros de insectos vectores como el mosquito A. aegypti por sus características insecticidas y el bajo impacto sobre organismos no blanco y la salud humana. Está claro que su potencial en el control de vectores reside en su efecto larvicida más que en su actividad ovicida.

          Translated abstract

          The ovicidal and larvicidal effects of spinosad were studied in Aedes aegypti treated with concentrations of 0.1, 5 y 10 ppm spinosad (Tracer 480SC) during different periods of exposure at a constant temperature of 25±1ºC. In a frst experiment the ovicidal effects were low (6.6-8.2% of non-eclosion averaged over 12-96h exposure periods), whereas in a second experiment ovicidal effects were moderate (27,9 - 31,9% of non-eclosion in eggs exposed to spinosad suspension of 1-12 weeks old). Mortality of larvae increased significantly with increasing concentration and increasing duration of exposure to this product. Although spinosad has clear applications as a mosquito control product for control of vectors such as A. aegypti, it is clear that its vector control potential resides in its larvicidal effects rather than its ovicidal activity.

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          A mutation in the voltage-gated sodium channel gene associated with pyrethroid resistance in Latin American Aedes aegypti.

          Pyrethroids are commonly used as mosquito adulticides and evolution of resistance to these compounds is a major threat to public health. 'Knockdown resistance' to pyrethroids (kdr) is frequently caused by nonsynonymous mutations in the voltage-gated sodium channel transmembrane protein (para) that reduce pyrethroid binding. Early detection of kdr is critical to the development of resistance management strategies in mosquitoes including Aedes aegypti, the most prevalent vector of dengue and yellow fever viruses. Brengues et al. described seven novel mutations in hydrophobic segment 6 of domain II of para in Ae. aegypti. Assays on larvae from strains bearing these mutations indicated reduced nerve sensitivity to permethrin inhibition. Two of these occurred in codons Iso1011 and Val1016 in exons 20 and 21 respectively. A transition in the third position of Iso1011 encoded a Met1011 replacement and a transversion in the second position of Val1016 encoded a Gly1016 replacement. We have screened this same region in 1318 mosquitoes in 32 additional strains; 30 from throughout Latin America. While the Gly1016 allele was never detected in Latin America, we found two new mutations in these same codons. A transition in the first position of codon 1011 encodes a Val replacement while a transition in the first position of codon 1016 encodes an Iso replacement. We developed PCR assays for these four mutations that can be read either on an agarose gel or as a melting curve. Selection experiments, one with deltamethrin on a field strain from Santiago de Cuba and another with permethrin on a strain from Isla Mujeres, Mexico rapidly increased the frequency of the Iso1016 allele. Bioassays of F(3) offspring arising from permethrin susceptible Val1016 homozygous parents and permethrin resistant Iso1016 homozygous parents show that Iso1016 segregates as a recessive allele in conferring kdr. Analysis of segregation between alleles at the 1011 and 1016 codons in the F(3) showed a high rate of recombination even though the two codons are only separated by a ~250 bp intron. The tools and information presented provide a means for early detection and characterization of kdr that is critical to the development of strategies for resistance management.
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            Embryonic desiccation resistance in Aedes aegypti: presumptive role of the chitinized Serosal Cuticle

            Background One of the major problems concerning dengue transmission is that embryos of its main vector, the mosquito Aedes aegypti, resist desiccation, surviving several months under dry conditions. The serosal cuticle (SC) contributes to mosquito egg desiccation resistance, but the kinetics of SC secretion during embryogenesis is unknown. It has been argued that mosquito SC contains chitin as one of its components, however conclusive evidence is still missing. Results We observed an abrupt acquisition of desiccation resistance during Ae. aegypti embryogenesis associated with serosal cuticle secretion, occurring at complete germ band extension, between 11 and 13 hours after egglaying. After SC formation embryos are viable on dry for at least several days. The presence of chitin as one of the SC constituents was confirmed through Calcofluor and WGA labeling and chitin quantitation. The Ae. aegypti Chitin Synthase A gene (AaCHS1) possesses two alternatively spliced variants, AaCHS1a and AaCHS1b, differentially expressed during Ae. aegypti embryonic development. It was verified that at the moment of serosal cuticle formation, AaCHS1a is the sole variant specifically expressed. Conclusion In addition to the peritrophic matrix and exoskeleton, these findings confirm chitin is also present in the mosquito serosal cuticle. They also point to the role of the chitinized SC in the desiccation resistance of Ae. aegypti eggs. AaCHS1a expression would be responsible for SC chitin synthesis. With this embryological approach we expect to shed new light regarding this important physiological process related to the Ae. aegypti life cycle.
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              Cost-comparison of DDT and alternative insecticides for malaria control.

              In anti-malaria operations the use of DDT for indoor residual spraying has declined substantially over the past 30years, but this insecticide is still considered valuable for malaria control, mainly because of its low cost relative to alternative insecticides. Despite the development of resistance to DDT in some populations of malaria vector Anopheles mosquitoes (Diptera: Culicidae), DDT remains generally effective when used for house-spraying against most species of Anopheles, due to excitorepellency as well as insecticidal effects. A 1990 cost comparison by the World Health Organization (WHO) found DDT to be considerably less expensive than other insecticides, which cost 2 to 23 times more on the basis of cost per house per 6 months of control. To determine whether such a cost advantage still prevails for DDT, this paper compares recent price quotes from manufacturers and WHO suppliers for DDT and appropriate formulations of nine other insecticides (two carbamates, two organophosphates and five pyrethroids) commonly used for residual house-spraying in malaria control programmes. Based on these 'global' price quotes, detailed calculations show that DDT is still the least expensive insecticide on a cost per house basis, although the price appears to be rising as DDT production declines. At the same time, the prices of pyrethroids are declining, making some only slightly more expensive than DDT at low application dosages. Other costs, including operations (labour), transportation and human safety may also increase the price advantages of DDT and some pyrethroids vs. organophosphates and carbamates, although possible environmental impacts from DDT remain a concern. However, a global cost comparison may not realistically reflect local costs or effective application dosages at the country level. Recent data on insecticide prices paid by the health ministries of individual countries showed that prices of particular insecticides can vary substantially in the open market. Therefore, the most cost-effective insecticide in any given country or region must be determined on a case-by-case basis. Regional coordination of procurement of public health insecticides could improve access to affordable products.
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                Author and article information

                Journal
                rcen
                Revista Colombiana de Entomología
                Rev. Colomb. Entomol.
                Sociedad Colombiana de Entomología (Bogotá, Distrito Capital, Colombia )
                0120-0488
                2665-4385
                December 2011
                : 37
                : 2
                : 269-272
                Affiliations
                [03] Tapachula Chiapas orgnameCentro Regional de Investigación en Salud Pública México fma-rina@ 123456insp.mx
                [02] Tapachula Chiapas orgnameECOSUR México
                [01] Tapachula Chiapas orgnameUniversidad Autónoma de Chiapas orgdiv1Facultad de Ciencias Químicas México
                Article
                S0120-04882011000200019 S0120-0488(11)03700219
                ff514f3a-df6b-4292-a8cc-eae0ae2a5efd

                This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

                History
                : 17 August 2010
                : 22 April 2011
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 16, Pages: 4
                Product

                SciELO Colombia

                Self URI: Texto completo solamente en formato PDF (ES)
                Categories
                Sección médica

                Dengue,Toxicidad,Mortalidad,Control de vectores,Toxicity,Mortality,Vector control

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