No description available.

RNA interference (RNAi) is a gene silencing mechanism induced by double-stranded RNA (dsRNA). RNAi has been used extensively to create loss-of-function mutants in many species to identify the functions of genes, but it also has the potential to be used as a species-specific pesticide if the dsRNA can silence essential genes in pests. The mosquito Aedes aegypti is a vector of numerous viruses including Dengue and West Nile virus, and is frequently controlled by chemical insecticides. With growing concerns about the extensive use of broad-spectrum pesticides, new control methods are eagerly sought. In this study, I examined the efficacy of feeding pesticidal dsRNAs to mosquito larvae. A dose-dependent RNAi response and mortality was observed when larvae were fed dsRNA targeting several different genes. Unlike RNAi in the related dipteran Drosophila melanogaster, RNAi in A. aegypti also appeared to be systemic, spreading beyond the gut to other tissues. A degree of species-specificity was also observed, as dsRNA specific to the D. melanogaster β-tubulin gene killed D. melanogaster larvae but did not kill mosquito larvae. RNAi was also used to determine the function of a newly-identified A. aegypti cytochrome P450 (CYP) gene, Aacyp. This gene showed male-biased expression in the mosquitoes, and was expressed primarily in the male abdomen and/or thorax, but unlike some other insect male-biased CYPs, Aacyp was not highly expressed in the reproductive structures. While dsRNA injections successfully knocked down expression of Aacyp, no discernable change in reproductive or male-specific behaviours were noted. Nevertheless, RNAi is still considered a highly versatile tool for both gene function studies and has promising potential to be developed into a novel class of pesticides.

RNA interference (RNAi) is a gene silencing mechanism induced by double-stranded RNA (dsRNA). RNAi has been used extensively to create loss-of-function mutants in many species to identify the functions of genes, but it also has the potential to be used as a species-specific pesticide if the dsRNA can silence essential genes in pests. The mosquito Aedes aegypti is a vector of numerous viruses including Dengue and West Nile virus, and is frequently controlled by chemical insecticides. With growing concerns about the extensive use of broad-spectrum pesticides, new control methods are eagerly sought. In this study, I examined the efficacy of feeding pesticidal dsRNAs to mosquito larvae. A dose-dependent RNAi response and mortality was observed when larvae were fed dsRNA targeting several different genes. Unlike RNAi in the related dipteran Drosophila melanogaster, RNAi in A. aegypti also appeared to be systemic, spreading beyond the gut to other tissues. A degree of species-specificity was also observed, as dsRNA specific to the D. melanogaster β-tubulin gene killed D. melanogaster larvae but did not kill mosquito larvae. RNAi was also used to determine the function of a newly-identified A. aegypti cytochrome P450 (CYP) gene, Aacyp. This gene showed male-biased expression in the mosquitoes, and was expressed primarily in the male abdomen and/or thorax, but unlike some other insect male-biased CYPs, Aacyp was not highly expressed in the reproductive structures. While dsRNA injections successfully knocked down expression of Aacyp, no discernable change in reproductive or male-specific behaviours were noted. Nevertheless, RNAi is still considered a highly versatile tool for both gene function studies and has promising potential to be developed into a novel class of pesticides.

No description available.

A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, South Africa in fulfilment of the requirements for the degree of Master of Science. 2016 / This project explored the ecological conditions of aquatic breeding sites of Anopheles gambiae sensu lato immatures in the Lowveld region of eastern Mpumalanga Province, South Africa. The aim was to determine the environmental conditions influencing anopheline abundance as well as abiotic parameters which associated with vector productivity. In addition to this, the levels of insecticide resistance to the three dominant compounds used in vector control in the region were assessed. Taking into account the sympatric occurrence of the major malaria vector in South Africa (An. arabiensis Patton) and its sibling, non-vector species (An. quadriannulatus Theobald), a laboratory study was devised which investigated the outcome of intra- and inter-specific competition under constant and fluctuating temperature regimes. There was a heterogenous distribution of anophelines across aquatic habitats in Mpumalanga with small-scale variation in salinity and Total Dissolved Solids (TDS) influencing species composition and Anopheles arabiensis was found in all sites surveyed with low numbers occurring where salinity levels were elevated. Anopheles merus associated with high salinity and TDS (Pearson’s Product Moment, r = 0.922, p < 0.05) whilst An. quadriannulatus dominated in breeding sites within 50m of a building or road. Anopheles gambiae complex members were susceptible to the insecticides tested with possible resistance (97%) to DDT in An. merus. Under laboratory conditions, temperature and competitive scenarios affected the life-history traits of both species studied here. The treatment 18 - 35°C generally reduced survivorship except for An. arabiensis in mixed, larval species treatments where it was similar to values reported for 25°C. Survivorship of both species at 20 - 30°C was not significantly impacted and the adult production was high across species treatments. The development rates at 25°C and 20 - 30°C were significantly different between species when reared alone and in mixed species treatments from larvae and from eggs. The effect of temperature was more pronounced at 18 - 35°C with An. arabiensis developing faster under both competitive scenarios and An. quadriannulatus slower, notably when in the presence of its competitor (p < 0.05). In the field component of this study, Anopheles arabiensis exploited all the habitats surveyed. It is therefore recommended that larval control operations should include all available breeding sites, focusing efforts during the dry season when these sites are limited and discreet within the landscape. In the laboratory component, it was possible to test whether or not community composition of anophelines at the adult stage was regulated by different temperature and competitive conditions at the larval stage to better understand the ecological conditions that determine anopheline composition and relative abundance. Taken together, the results of each component emphasize the need for local scale studies, especially under conditions of changing temperatures and rainfall patterns. The results of responses to temperatures and biotic interactions are necessary data for use in models predicting the impact of climate change on malaria vector mosquitoes. / MT2016

Thesis (M.P.H.)--University of Michigan, 1946.

Thesis (M.P.H.)--University of Michigan, 1946.

Long-term insect abundances have been studied to investigate factors structuring the insect communities of the temporary wetlands around the River Dalälven floodplain. In the wet meadows and swamps in the River Dalälven floodplains recurrent floods are the ultimate prerequisite for high production of floodwater mosquitoes. In the larval stages these make up a superabundant potential prey for aquatic predatory insects while as adults they become nuisance for people and animals. Mosquito control with Bacillus thuringiensis israelensis (Bti) has been carried out in parts of the floodplain wetlands since 2002. This study investigate potential long-term effects of Bti on non-target insects in general, and non-biting midges (Diptera: Chironomidae) and aquatic predator insects in special in 10 temporary wetlands. Diving-beetles (Coleoptera: Dytiscidae) were the most common aquatic predatory insects in temporary flooded wetlands, and we found no indications that diving-beetles were negatively affected by mosquito larvae reduction with Bti-treatments. Non-target Bti-effects on the insect community in general, measured as increase or decrease of insect abundances, in general showed no effects of Bti except for Coleoptera. The non-biting midges were studied on species level, since this taxon previously has been associated with negative Bti non-target effects in the short-term. We found no reduced production of chironomids at neither family, nor subfamily level in Bti-treated as compared to untreated wetlands. We conclude that other factors than the occasional Bti-treatments dominate in structuring the chironomids fauna. For example, hydrology measured as floods and hydroperiod had substantial impact on insect emergence Increased hydroperiod was associated with lower insect emergence for the majority of the studied taxa, indicating an insect fauna adapted more to terrestrial conditions. In the final study, we developed and applied a molecular method to study interspecific predator – prey relationships between medium-sized diving beetles and floodwater mosquito larvae. Gut content analyses showed that floodwater mosquito larvae are a regular, but limited, part of the diet of medium-sized diving beetles. This thesis is one of the first long-term studies of insects of temporary wetlands in relation to mosquito control actions. The results indicate that hydrology is one of the major factors influencing and structuring the insect communities of the temporary flooded wetlands in the River Dalälven floodplains, and that mosquito control actions with Bti only have marginal effect on insect abundances.

Insecticide resistance in malaria vector mosquitoes reduces the efficacy of insecticide in killing and can therefore cause a major problem for malaria vector control by insecticides. In Mozambique, pyrethroid resistance in Anopheles funestus was first detected in December 1999 in the southern corner of Maputo Province. Since then, various collections have been made at selected sites throughout the country and WHO standard susceptibility tests and biochemical assays were conducted to determine the susceptibility status and the major resistance mechanisms, in the Fl generation of field collected mosquitoes. Three malaria vector species: Anopheles funestus s.s., Anopheles gambiae s.s. and Anopheles arabiensis were identified in this study by Polymerase Chain Reaction (PCR) and their distributions plotted. The susceptibility data indicate that the Anopheles funestus s.s population in southern Mozambique is widely resistant to pyrethroid and with low levels of carbamate resistance evident at six localities. No resistance to organophosphate and DDT was observed at any study sites. Biochemical tests indicate the presence of an altered acetlylcholinesterase in all collection localities with the exception of Massinga district. Elevated esterase activity with substrate a-naphthyl acetate were detect in Boane with a probable role in organophosphate resistance. Elevated GST were detected in Boane, Moamba and Catembe. Very low levels monooxygenase titres were registered in all the localities in Mozambique, which suggest that this resistance mechanism is not operating in these areas. Pyrethroid resistance in the Anopheles gambiae complex was detected only in Anopheles arabiensis from one locality. No resistant to other groups of insecticide were observed. Altered acetlylcholinesterases were registered in all collection localities and in both species: Anopheles gambiae s.s. and Anopheles arabiensis. Elevated esterase with substrate a-naphthyl acetate were detected in Anopheles arabiensis at only one locality. Elevated GSTs were detected at all localities and in both species. The implications of the findings for malaria vector control in Mozambique are discussed. / Thesis (M.Sc.)-University of Natal, Durban, 2003.

Thesis (M.P.H.)--University of Michigan, 1948.