In Port-au-Prince, Haiti, the status of insecticide resistance has not recently been evaluated for Aedes aegypti (L) and Aedes albopictus (Skuse) populations. No prophylactics exist for dengue, so prevention is only through vector control methods. An earthquake occurred in Haiti on January 12, 2010, with a magnitude of 7.0 Mw that devastated the area. Dengue became a major concern for the humanitarian relief workers that entered the country. Bottle bioassays were conducted in the field on adult mosquitoes reared from larvae collected from the grounds of the U.S. Embassy and from an adjacent neighborhood in eastern Port-au-Prince, Haiti. At the CDC, Fort Collins, CO, bioassays, molecular, and biochemical assays were performed on mosquitoes reared from field-collected eggs. A small percentage of the population was able to survive the diagnostic dose in bioassays run in Haiti. Mosquitoes tested at the CDC demonstrated no phenotypic resistance. A variety of factors could be responsible for the discrepancies between the field and lab data, but temperature and larval nutrition are probably most important. Knowledge of localized resistance and underlying mechanisms helps in making rational decisions in selection of appropriate and effective insecticides in the event of a dengue outbreak. Journal of Vector Ecology 37 (2): 325-332. 2012.
Insecticide resistance to organophosphates and carbamates can be the result of changes in acetylcholinesterase activity conferred by the ACE-1 mutation. Detection of this altered target site mutation is important in guiding informed decisions for resistance management. In this study we compared a competitive enzyme assay with a polymerase chain reaction assay utilizing a restriction enzyme. Both assays detected the ACE-1 mutation in Culex quinquefasciatus and agreement was 100%. The costs and benefits of each assay are presented. KeywordsCulex quinquefasciatus; acetylcholinesterase; organophosphate resistance; ACE-1 mutation Because of biological fitness costs usually associated with insensitivity of target sites to insecticides, insects carrying modified target site gene(s) generally remain at a low frequency in the absence of selection pressure. Remarkably, it is only minor changes in the gene(s), often a single base change, which make target proteins (enzyme or receptor) insensitive to insecticides (Chaudhry and MacNicoll 1998). The gene, ACE-1, is present worldwide and causes organophosphate (OP) and carbamate resistance. A high level of acetylcholinesterase (AChE)-1 protein insensitivity or resistance displayed in Culex pipiens L. is due to a single amino acid substitution, G119S, a mutation in the 3rd exon of the ACE-1 gene, leading to the replacement of a glycine (GGC, susceptible allele) by a serine (AGC) (Weill et al. 2003(Weill et al. , 2004. This mutation is associated with reduced susceptibility to OP insecticides, modifications of the catalytic properties of AChE-1, and a high fitness cost (Weill et al. 2003). Understanding the underlying resistance mechanisms is important in making informed decisions on alternative control strategies. In our current economic situation, with funding and programs being cut, it is important to have access to a variety of different testing methods for detecting mechanisms of resistance depending on one's budget, personnel, and time. In this study we compare a biochemical assay used in our laboratory HHS Public Access Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript with a molecular assay, both of which detect resistance due to insensitive acetylcholinesterase. We evaluated not only the efficacy of each assay, but also calculated the time, cost, and skill level each assay required. Culex quinquefasciatusSay egg rafts were collected in Harris County, TX from 2004 through 2008. Mosquitoes were reared in incubators at 27.5°C, 80-85% RH, and 14 : 10 light : dark cycle. They were aspirated into 1.5-ml microtubes 1-2 wk after they had emerged and stored in a −80°C freezer (Thermo Scientific, Waltham, MA) for future use. Fifteen mosquitoes from each collection site throughout Harris County were tested, for a total sample size of 300. In order to compare the competitive enzyme assay to the polymerase chain reaction (PCR) assay, the same mosquitoes were used for both tests. For the PCR assay and sequencing, all 6 legs were removed from the females,...
Insecticides based on botanical sources have taken on increased attention due to differing modes of action from current insecticides in use and the view that they may be environmentally friendly. Thymoquinone, a component in the essential oil of incense cedar heartwood, has been shown to have insecticidal action against adult mosquitoes. This study evaluated relative toxicities of thymoquinone, selected derivatives of thymoquinone, hydroquinone, and arbutin to determine if any had similar or better activity. The intrinsic toxicities of hydroquinone and thymohydroquinone were not significantly different from thymoquinone, while libocedrol and arbutin were significantly less toxic.
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