The association of olfactory information with a resource is broadly known as olfactory-based associative learning. From an ecological perspective, associative learning can reduce search time for resources and fine tune responses to changing biotic and abiotic factors in a variable environment, which in mosquitoes has implications for pathogen transmission and vector control strategies. The purpose of this dissertation was to examine the ability for olfactory-based associative learning across the major life history domains of mosquitoes. Six different experiments comprise this dissertation. The first was to evaluate the response of mosquitoes following conditioning to 5, 10 or 50% sucrose concentrations with individual level mosquito conditioning and testing and introduction of statistical analysis with binary logistic regression. Mosquitoes did not respond in a dose dependent manner with respect to positive response to target odors following conditioning. This effect appears to be related to the mosquitoes' prior exposure to sugar as those exposed to 10% sucrose before conditioning did not prefer 50% sucrose but significantly fewer chose 5% sucrose. In an evaluation of host associated odors and second blood meal choice by females using a dual-choice olfactometer no significant effects were observed. The lack of significance may have been due to insufficient sample sizes, problems with odor collection or physiological state of mosquitoes. Effects of predatory mosquitofish on larval development and female oviposition choice were evaluated by rearing in separated habitats under three different treatments followed by an oviposition choice assay. Females did not prefer their natal habitat or avoid predators but chose substrate that had contained mosquitofish fed conspecific larvae. Mosquitofish affected larval development with acceleration in treatments with mosquitofish fed Tetramin® and delayed pupation in treatments with mosquitofish fed conspecific larvae. Mosquito memory length was evaluated by conditioning and testing at six time intervals from colony and field populations at two ages. Younger mosquitoes showed higher levels of positive response after conditioning at all time intervals except the longest (24h). Finally the olfactory-based associative learning ability of Anopheles cracens was evaluated. Significant evidence for learning was observed in males but not females at a memory length interval of 24h.

Harris County Mosquito Control Division (HCMCD) is responsible for surveillance of mosquito species that are vectors of St. Louis Encephalitis (SLE) virus and West Nile Virus (WNV) within Harris County, Texas, including the Houston metroplex. The metroplex area has some unique attributes and a vast variety of environmental habitats that are attractive to vectors of arboviruses and for the transmission of arboviruses to the human population. Data describing the efficacy of Gravid (GV) and Underhouse (UH) CO2 traps were analyzed to determine if there is a significant difference between these two trap types with respect to the number of mosquitoes and the variety of mosquito species caught. This study was conducted during the off-peak HCMCD trapping season, to gain information in preparation for a yearround trapping program utilizing Underhouse CO2 traps for WNV and SLE virus surveillance. Adjusting for the week of collection, results suggest that Gravid traps caught significantly (P = 0.009) more mosquitoes (mean = 23.134 per trap) in the study area than Underhouse traps (mean = 3.616 per trap), and that Underhouse Traps caught a larger variety of mosquito species (n = 13) than Gravid Traps (n = 11), out of 15 total different species caught. Gravid and Underhouse traps caught 9 out of 15 of the same mosquito species during the study period. Culex quinquefasciatus mosquito catches in Gravid traps and temperature were strongly correlated (Spearman's Correlation Coefficient = 0.707, P = 0.005). Geographic Information System spatial analysis indicated clustering of Culex quinquefasciatus mosquito catches in both Gravid traps, week 9 and 21 (Moran's I = 0.69, P = 0.040 and 0.74, P = 0.021, respectfully ) and Underhouse traps, week 13 and 19 (Moran's I = 0.92, P = 0.002, and 0.89, P = 0.011, respectfully). It is recommended that Harris County Mosquito Control Division continue to utilize gravid traps as a primary method of surveillance. Gravid traps (16,194) caught 85% more mosquitoes than Underhouse traps (2,531) over the fourteen week study period. Their overall success far outweighs the additional materials or labor required for their use in a successful surveillance program.

<p>New and old mosquito-borne diseases have emerged and re-emerged in temperate regions over the recent past, but an understanding of mosquito population dynamics, a fundamental step toward disease control, remains elusive. In particular, we are still lacking reliable predictive models of mosquito abundance in temperate areas due to the subtle links between the fluctuation of mosquito population and highly heterogeneous environmental drivers. Hence, this doctoral dissertation presents an interdisciplinary approach towards an improved understanding and prediction of the fluctuations in mosquito abundance in temperate regions. In the first part of this dissertation a hierarchical Gompertz-based model is used to assess the relative importance of endogenous (density dependence) and exogenous (environmental forcings) controls and their interactions in regulating the dynamics of a West Nile Virus vector (Culex pipiens) in the Po River delta in Italy. The results clearly detect the effects of density-dependence in the observed population dynamics for the mosquito species analyzed and highlight the controls exerted by environmental forcings and habitat conditions. Subsequently, the characteristic scales of temporal variability in mosquito populations, and the representativeness of observations at different sampling resolutions, are investigated using a 10 year daily mosquito sample from Brunswick County, North Carolina. The species present in the sample (among which Aedes vexans and Culiseta melanura are addressed in greater detail, as vectors of East Equine Encephalitis and West Nile Virus) are investigated using a combination of time series analysis, individual based simulations, and density-dependent modeling approaches. Significant population fluctuations with characteristic periodicity between 2 days and several years are found in response to different regulation mechanisms. In particular, the observed fast fluctuations are importantly determined by a varying mosquito activity, rather than by reproduction/mortality processes, driven by rapid changes in meteorological conditions. Finally, in the third part of this study, a state space reconstruction (SSR) approach is used to understand how the predictability of mosquito abundance varies with aggregation time scale and with the prediction horizon, and how much can the prediction of mosquito abundance be improved by using daily observations compared to the commonly used once-per-week samples. The results show that the predictability of mosquito abundance decreases as the time scale of the models increases from one week to one month, while the predictability of per capita growth rate increases together with the modeling scale. It is also shown that the prediction of mosquito per capita growth rate can be improved using daily abundance observations. Furthermore, many mosquito models compare the observed and predicted abundance as a measure of model performance. However, my results suggest that short term forecasts of mosquito abundance may appear to have a significant capability due to the positive autocorrelation between abundance in subsequent time steps, even when the model's ability to predict the abundance change is low. Model capability should thus be evaluated comparing observed and modelled per capita rates of change.</p> / Dissertation

Mosquitoes spread diseases that shorten and worsen the lives of many people, chiefly children in poor countries, around the world. Since Ronald Ross' discovery at the end of the nineteenth century that mosquitoes transmit malaria, field entomologists have collected a great deal of information about mosquito ecology. Despite this tremendous effort, there still remain significant gaps in our knowledge of mosquito ecology, in part, reflecting the significant variation in mosquito ecology across species and geographies. The main aim of this thesis is an attempt to synthesise the substantial information that field entomologists have collected on mosquito lifespan. In Chapters 2 and 3, I conduct meta-analyses of the two predominant approaches used to estimate mosquito lifespan: mark-release-recapture experiments and female mosquito dissection-based studies, respectively. These analyses produce estimates of mosquito lifespan by species and genus, and more broadly, allow for an appraisal of these two experimental approaches. In Chapter 4, I describe a recently developed approach, known as near-infrared spectroscopy, which enables estimation of the age of individual mosquitoes, and then perform an in silico analysis to explore the use of this technology for estimating the average lifespan of wild populations of mosquitoes. The emergence of mosquito resistance to the main insecticides used in vector control, along with the concerning recent discovery that the malaria parasites in Asia are becoming resistant to arteminisin - an important drug used to treat malaria - highlight the need for novel approaches to control disease transmission. Some recently-proposed approaches involve genetic modification of the mosquito vectors, for example, to render them incapable of acting as hosts for disease or to reduce their fecundity. In Chapter 5, I model the impact of a release of mosquitoes carrying a genetic construct known as a homing endonuclease, which has been constructed to bias the sex of mosquito offspring towards males, in computational environments that capture some facets of the real life landscapes where mosquito borne disease is rife. About a century ago, the famous Italian Malariologist Giovanni Grassi declared that malaria was a "giant with clay feet"; reflecting the optimism, in some academic circles at the time, that eradication of this terrible disease would soon occur. Unfortunately, a century of often unsuccessful attempts to control and eradicate malaria, and other mosquito borne diseases, would follow Grassi's statement, meaning that this fight is likely to continue throughout the twenty-first century. We now know much more about mosquitoes and mosquito borne disease than we did a generation ago, but there is still crucial information that we do not. In this thesis, I argue that in order to make significant inroads to disease eradication, further research on mosquito ecology is crucial. Only when we better understand our unwitting mosquito foe, can we design and implement effective disease control measures that are so desperately needed in those most desperate parts of the world.

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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.

Every year over two hundred million cases of malaria occur worldwide causing human death and suffering often in the poorest countries. Most people who die from malaria are children under five years of age. Malaria is caused by parasites spread by mosquitoes when they feed on human blood. Currently prevention methods include insecticides and anti-malarial drugs. The problem with both is the increasing resistance towards them by mosquitoes and parasites, respectively. Therefore other approaches need to be investigated to find new solutions to this problem. One such research area is paratransgenesis, the genetic modification of symbiotic microorganisms in the mosquitoes to produce anti-malaria parasite molecules. One bacterium identified as a potential candidate for paratransgenesis is Thorsellia anophelis. When this study started, only one Thorsellia isolate existed in the world. The aim of this study was therefore to retrieve more Thorsellia isolates from Kenyan mosquito and water samples. The samples were screened by PCR followed by bacterial culturing of positive samples, which resulted in 38 new Thorsellia isolates confirmed by DNA sequencing. The isolation of new Thorsellia species enables further investigation of the potential for their use in paratransgenesis with the aim of contributing to the prevention of malaria transmission.

West Nile virus (WNV) is a geographically endemic mosquito-borne flavivirus that has spread across the United States infecting birds, mosquitos, humans, horses and other mammals. The wide spread nature of this virus is due to the ability of the mosquito vector to persist in broad, ecological diverse environments across the United States. In this study, mosquito populations in North Texas region were sampled for detection of Wolbachia, blood meal source, and WNV. The ultimate goal of this study was to examine the potential of a biocontrol agent, Wolbachia sp. that colonizes the hindgut of various insects, including mosquitos, as a natural means to interrupt virus transmission from mosquitos to other hosts, including humans. In Australia, Wolbachia sp. from fruit flies (Drosophila melanogaster) have been successfully used to block transmission of a similar pathogenic virus from mosquitos responsible for transmission of Dengue fever. Here, mosquitoes were collected using CDC style Gravid Traps in Denton, Texas, from October 2012 through September 2014. Collected mosquitoes were identified, sexed, and categorized as to the amount of host blood in their alimentary system using a Zeiss Axio Zoom microscope (Carl Zeiss Microscopy, LLC, Thornwood, NY). Culex quinquefaciatus was the dominant blood engorged species collected. Smaller populations of Culex tarsalis and Aedes albopictus, another known vector for WNV were also collected. Mosquito larva were also collected from the UNT water research field station and reared to adults. Cx. tarsalis was the dominant mosquito taken from this habitat. Samples of Cx. quinquefasciatus, Cx. tarsalis and A. albopictus were analyzed for Wolbachia sp. and to identify host blood in the mosquito alimentary system. Total DNA extraction from the pool of mosquito samples was by both commercially available DNA extraction kits (Qiagen, Valencia, CA) and salt extraction technique. Polymerase chain reaction (PCR) was used to amplify and identify Wolbachia sp. 16SrDNA and mitochondrial DNA from vertebrate blood. The maternally inherited endosymbiont, Wolbachia, were found to be uniformly distributed across the mosquitoes sampled in this study. Blood meal analysis by PCR showed that Cx. quinquefaciatus fed more on birds than on mammalian blood sources based on the previously developed primers used in this study.