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Browsing Theses and Dissertations by Subject "Aedes albopictus"

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    Permethrin resistance status and associated mechanisms in Aedes albopictus mosquitoes: implications for vector control
    (Colorado State University. Libraries, 2020) Janich, Ashley J., author; Kading, Rebekah C., advisor; Foy, Brian D., committee member; Dayan, Franck E., committee member
    There are major public health concerns regarding the spread of mosquito-borne diseases such as dengue, Zika, and chikungunya. The primary method to reduce the spread of these diseases is by killing the major mosquito vectors, Aedes aegypti and Aedes albopictus, with insecticides. However, with continued use of insecticides, these species have started developing resistance to the toxic effects of insecticides and higher concentrations and doses are needed to continue to effectively control these vectors. One of the insecticides that is frequently used to control these mosquitoes is permethrin, a type I pyrethroid, due to its rapid knock down effect and its low toxicity to mammals and other vertebrates. Resistance has been extensively studied in Ae. aegypti from various countries around the world. However, there are comparatively fewer studies that have examined resistance in Ae. albopictus mosquitoes, especially in the Americas. In this study, we wanted to investigate the permethrin resistance status of Ae. albopictus mosquitoes collected from Southern Mexico and Southern Texas. Additionally, we also wanted to test if permethrin resistance could be artificially selected in the laboratory over several generations. Lastly, we wanted to investigate the potential mechanisms that have been found to previously confer resistance in other mosquitoes. The two mechanisms that were investigated were knock down resistant (kdr) mutations, specifically the F1534C mutation of the voltage gated sodium channel (VGSC) gene, and the activity of metabolic enzymes that break down and detoxify insecticides. We found that there were low levels of resistance in our populations of Ae. albopictus from Mexico and Texas, with resistance ratios (RRs) ranging from 1.18 to 2.40 relative to our control strain, ATMNJ95. The results of our selected strain were unexpected. There was a gradual increase in the RR over several generations of selection, but our last selected generation had a lower RR compared to the previously selected generations. We did not find the F1534C mutation in any of our Ae. albopictus strains from Mexico. There was significantly higher cytochrome P450 activity in our permethrin-selected and non-selected strains of Ae. albopictus from Mexico compared to our control strain. The same pattern was also observed in the counterpart Ae. aegypti strains that were analyzed for comparison. Our results suggest that Ae. albopictus from the regions we sampled are still mostly susceptible to pyrethroids. However, it is possible we are observing beginning stages of resistance in this species. Alternatively, we also acknowledge the possibility that there might be ecological or historical differences between Ae. albopictus and Ae. aegypti that have resulted in different levels of resistance between the two species. It is important to continue monitoring populations of Ae. albopictus in order to prevent the development of resistance in the future.
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    Vector and virus interactions: La Crosse encephalitis virus and the mosquito vector Aedes (stegomyia) albopictus
    (Colorado State University. Libraries, 2008) Sutherland, Ian W., author; Beaty, Barry J., advisor
    La Crosse encephalitis continues to be an important cause of pediatric arboviral encephalitis in the United States. Since 1985, the invasive mosquito vector, Aedes albopictus, has spread across the country and into La Crosse virus endemic regions. As an aggressive, daytime feeder, this vector has the potential to change the epidemiology of La Crosse encephalitis. This study investigated 4 components of the La Crosse virus- Ae. albopictus system: (1) time course of disseminated and filial infection rates (FIR) among recently colonized field strains, (2) anatomic basis of ovarian infection during the 1st gonotrophic cycle, (3) mitochondrial DNA (mtDNA) variation among geographically dispersed populations in the U.S., and (4) development of transovarially susceptible and refractory strains of Ae. albopictus. All geographic strains tested are susceptible to La Crosse virus oral infection and capable of transovarial transmission (TOT). No regional or geographic patterns emerged with respect to dissemination or TOT. 1st gonotrophic cycle vertical transmission was observed at low levels, with an FIR averaging 1%. 2nd gonotrophic cycle FIR averaged approximately 10% and was significantly lower than that of the natural vector, Ae. triseriatus. La Crosse virus antigen (Ag) was detected in ovaries by Day 2 after oral infection and prior to detection in head tissues. Ag was not detected in follicles through Day 7, suggesting vertical transmission. Examination of variation in the ND5 mtDNA marker revealed high levels of homogeneity among U.S. Ae. albopictus populations. Only 2 haplotypes were observed from 16 geographically dispersed states, including Hawaii. Such broad homogeneity could be due to multiple factors, including founder effects and cytoplasmic incompatibility. Ae. albopictus responded poorly to selection based on FIR for the development of susceptible and refractory strains. This study supports prior literature suggesting Ae. Albopictus may be an important secondary vector of La Crosse virus.