Phenotypic Plasticity in Mosquito Populations: Potential for Disease Transmission

NON-TECHNICAL SUMMARY: Mosquitoes are responsible for transmitting the causative agents of some of the most widespread and prevalent infections of humans, including malaria, lymphatic filariasis, yellow fever, dengue fever, and the encephalitides. The significance of mosquito-borne disease transported internationally was dramatically imposed upon citizens of the United States during the outbreak of the West Nile virus in New York City and surrounding areas in 1999. In order to control populations of disease vectors and, in turn, control the disease agents they transmit, there must exist an extensive and thorough knowledge of the life cycle and ecology of these arthropods. Additionally, the increase in world travel and the threat of the ability of diseases to cross oceanic barriers demands the attention of science. Although not arthropod borne, the public awareness of SARS and Avian Bird Flu have brought to the forefront of people's awareness the threat of pandemics. There are approximately 2500 species of mosquito worldwide with roughly 150 species in the United States, including many species which participate in disease transmission cycles. Studies previously conducted at Lincoln University's Carver Farm have identified the presence of six genera of mosquitoes. Of these six, four have been implicated as enzootic vectors of various encephalitic diseases. Future research concerning the population densities, breeding habitats, and feeding habits of these genera of mosquitoes is necessary due to the growing concern over the hazards of potential outbreaks of mosquito borne diseases. This study will include trapping of adult females, comparing traditional CO2 baits with new chemical lures, and determining adult population densities and female fecundity as related to adult dry mass. In addition, larval populations in this area will be examined. Larval density will be examined by manual dipping procedures and a sampling of pupae will be reared in the laboratory for adult identification and determination of dry mass. The data collected in this research will be examined to estimate the adequacy of the pupation window model to estimate the influence of environmental factors on adult size and fecundity. By examining the biology of mosquitoes from the viewpoint of interactions between mosquito populations and the ecosystems in which they live, we can gain a better understanding of the role that environmental factors play in larval development, adult mosquito production and fitness, and population dynamics.

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APPROACH: 1) Adult mosquitoes will be collected using both CDC miniature black light traps baited with carbon dioxide and ground based traps baited with octanol. Trapping will occur twice a week for a minimum of 20 weeks. Larval habitats will be sampled weekly by manual dipping. Pupa will be isolated and reared to adulthood to confirm species. The bodies will be dried at 400C for 48 hours and weighed to the nearest 0.001 mg. <P> 2) Artificial microcosms representing larval mosquito habitats will be used to examine biotic and abiotic influences on larval development. Varying combinations of larval species, temperatures, resource availability and density will be examined. Consistent diurnal cycles and temperatures will be maintained. Each trial will consist of a 3 x 3 factorial design with six replicates in each category. Emerging adults will be dried and weighed as previously described. Male and female emergence, mean development time and mean body mass will be calculated. <P> 3) Wild strains of mosquitoes will be captured from geographic regions varying in latitude. Larvae or pupa will be collected and laboratory reared to the adult stage for species determination and potential creation of isolated laboratory strains. Experimental design from method 2 will be utilized to provide data for developmental parameters relative to the pupation window model. <P> 4) Variations in food supply and temperature affect development time to maturity and mass at metamorphosis in contrary ways in ectothermic animals. Using the pupation window model for larval mosquito development, we hope to be able to pin down the reaction norms to environmental conditions and use this information to better predict potential transmission or outbreak of disease. The results collected previously will be analyzed for significance using analysis of variance corresponding to the appropriate level of variables. In addition, scatter plots will be generated for each trial and compared to the current pupation window model. Environmental variation and genetic disparity can contribute to alterations of the extremes in the reaction norms for mosquitoes. This analysis can provide deeper understanding of the physiological and evolutionary bases for these relationships and further our understanding of environmental variability as a contributing factor to new and newly emerging epidemics. <P> 5) Strains showing wide diversity of character in development will be separated based on extended development time and/or decreased adult size. Genetic analysis comparing offspring for multiple generations can yield data regarding inheritance patterns, possibly the number of gene loci influencing the traits, and heritability statistics. Exploration of chromosome variation will begin with utilizing random amplified polymorphic DNA. Analysis of marker differences within and between populations uses Shannon's index of phenotypic diversity. Scoring of variation in bands as present or absent provides information about the organization of phenotypic patterns at group and population levels when analyzed using the Analysis of Molecular Variance. DNA sequencing can provide additional information.