The study presented in this dissertation concerns the epidemiology of eastern equine encephalitis (EEE) in Massachusetts. Human serosurveys were conducted in case neighborhoods to determine the inapparent infection rate and to test the hypothesis of focality of EEE virus transmission. An inapparent transmission rate of up to 1.85% was observed at epidemic foci. Focality of transmission was supported by the identification of an inapparent infection less than 10 meters from a 1990 case site. Putative epidemic EEE virus vector populations were compared at 15 case sites in Massachusetts. Carbon dioxide baited American Biophysics Corporation (ABC) light traps were used for trapping mosquitoes to estimate biting risk. These population data along with biological and behavioral data from other studies suggest that Coquillettidia perturbans (Walker), Aedes canadensis (Theobald), and Culex salinavius (Coquillett) may be more important vectors than the other potential vectors for EEE virus in Massachusetts, Aedes vexans (Meigen), Anopheles punctipennis (Say) and Anopheles quadrimaculatus (Say). Stepwise linear regression models were constructed from remotely sensed landscape data and Geographic Information System (GIS) Technology. Wetlands accounted for up to 72.5% of the observed variation in the host seeking populations of Ae. canadensis, Ae. vexans, and Culesita melanura. Stepwise linear regressions also demonstrated deciduous wetlands to be the specific wetland category contributing to the major class models. Pesticide targeting of deciduous (or coniferous) wetlands may be an effective way of controlling the abundance of Cs. melanura, Ae. canadensis and Ae. vexans. The effect of EEE virus on survivorship was determined for three possible epidemic vectors: Aedes albopictus, An. quadrimaculatus and Cq. perturbans. Female mosquitoes of these three species were exposed to EEE virus through infected blood meals and compared to uninfected controls for differential survival. Additionally, survival of Cq. perturbans and An. quadrimaculatus mosquitoes intrathoracically inoculated with EEE virus was compared to controls receiving diluent inoculations. It was shown that neither Ae. albopictus nor An. quadrimaculatus experienced reduced survivorship. Reduced survival was observed among Cq. perturbans orally infected with EEE virus. Damage to the midgut epithelium by EEE virus may be the cause of the increased mortality in this vector.

Gravids preferred oviposition sites that contain larvae over those that contain only water. The degree of preference increased with increasing larval instar, and also increased with increasing larval density up to a density of 2 larvae per ml. At higher densities the response became negative. Larvae act as indicators of site-suitability, and may indicate imminent competition at high densities, regardless of the presence of contaminating microfauna. Gravids rely on olfactory and chemo-tactile cues to detect the presence of larvae at oviposition sites, with a greater reliance on olfactory cues. Visual cues are unimportant in the detection of larvae. Gravids avoided ovipositing in a site already harboring eggs. This negative response increased with increasing egg density. Eggs are indicators of direct competition in the larval habitat. This avoidance reaction is mitigated by both olfactory and chemo-tactile cues. That egg distribution did not affect subsequent oviposition suggests the chemo-tactile response is more likely due to local concentration of chemicals than due to direct contact with eggs. Females visit more smaller sites when all available oviposition sites are identical, and lay fewer eggs in smaller treatment sites, than they do compared to larger sites. The gravid response is independent of substrate surface area and water volume. Eggs were not distributed differently in oviposition sites of different size but equal diameter, suggesting females may select different size-sites based on water surface area. Size is probably an indirect measure of available resources. The oviposition response does not vary with either chronological age of the gravid, nor with her gonotrophic cycle. Females separated in age by 2 weeks in post-emergence age or by 2 gonotrophic cycles responded to oviposition sites in the same manner. Oviposition behavior is flexible but does not take into account a female's relative fitness. The response to oviposition sites containing an attractive density of larvae was further investigated. Females could not discriminate between control and treatment sites in a wind tunnel, even when released but 22 cm from the attractive treatment. The olfactory cues associated with larval rearing habitat act as close range oviposition attractants.

Malaria occurs in a wide variety of environments. This tends to complicate the development of control strategies. In addition, vectorial capacity (the probability that a given vector will acquire, incubate, and transmit a disease organism) has been shown to vary greatly among both individuals and populations of vector species. Variability is influenced by both intrinsic and environmental factors. Understanding the effect of the environment on the vectorial capacity of mosquitoes would aid in the development and implementation of new control strategies. Body size and adult nutritional status of adult mosquitoes are two major factors thought to influence vectorial capacity. Both are influenced by changes in the environment. Various pesticides used in the control of mosquito populations also have been reported to influence acquisition and transmission of malaria parasites. Studies reported here focus on the impact of these extrinsic factors on the ability of the mosquito to acquire, incubate and transmit malaria parasites. Four hypotheses were tested in these experiments. These were: (1) large mosquitoes transmit malaria to more hosts during multiple feeding than small mosquitoes, (2) sugar taken before an infected blood meal and blood taken after an infected blood meal will increase acquisition and transmission of malaria, (3) mosquitoes exposed to sublethal doses of Bti will be less likely to acquire and transmit malaria than unexposed mosquitoes, and (4) developing oocysts promote the survivorship of the vector by inducing delays in subsequent egg-laying and blood-feeding. Two different models, an Anopheles stephensi - Plasmodium berghei - mouse model and an Aedes aegypti - Plasmodium gallinaceum - chicken model, were used to test these hypotheses. Both models were used to test the first hypothesis. This hypothesis was found to be true for Aedes aegypti. The hypothesis was also found to be true for Anopheles stephensi if the mosquitoes fed daily, but not true if they fed in quick succession. The Aedes aegypti model was used to test the second hypothesis. This hypothesis was not found to be true. The Anopheles stephensi model was used to test the third hypothesis. This hypothesis was not found to be true. The fourth hypothesis was tested using the Aedes aegypti model. The work presented here does not support the hypothesis. However, these experiments were preliminary, so more work is needed before any conclusions can be drawn.