The growth and production of adult mosquitoes from the aquatic larval habitats is constrained by conversion of refractile organic material into ingestible and digestible microbial biomass. Rates of conversion of organic matter into microbial biomass are tempered by the quality of particulate substrates that is manifested in dual roles of inhibition and stimulation of microbial and larval growth. Our long-term goal is to delineate the biological basis for and constraints on mosquito production, to identify the efficiency of utilization of these resources, and to elaborate a realistic model of larval growth. We have identified the tree hole ecosystem for study, harboring the species Ochlerotatus triseriatus, Ochlerotatus japonicus, and Culex pipiens, two vectors of human pathogens and one an exotic invader. Research approaches include an axenic (germ-free) experimental system into which individual food sources including microorganisms can be provisioned;stable isotopic analyses (13C/12C;15N/14N) to track larval foods to their sources;molecular analyses of microbial community structure;a functional gene array analysis of microbial genes encoding enzymes involved in large biomolecule degradation, including xylanases, cellulases, and chitinases;and microcosm and naturalistic experiments in which microbial biomass and metabolic activity relative to larval growth are quantified. A growth model is proposed in which developmental time to, and mass at, metamorphosis (i.e., pupation) are postulated to be flexible life history traits whose minima are nutritionally and genetically constrained into a pupation window defining body size and affecting adult survivorship;both are key fitness parameters and both important components of vectorial capacity. Experiments will delineate relationships among them, and reveal environmental and genetic components contributing to their variation. The current understanding of larval growth rates requires conversion efficiencies (mg food assimilated per mg food ingested) far higher than observed, thus we will iteratively test growth responses relative to natural microbial food sources of various qualities, fit observed growth data to models, and revise conversion efficiency estimates accordingly. The three mosquito species sharing the same larval habitat and resources will be compared to assess growth rates under conditions of intense intra- and interspecific competition, both to make predictions of competitive outcomes and potential for ecological displacement, and to quantify comparative efficiency of utilization of larval foods. Manipulation of the Flavobacterium component of the microbial community a dominant member with molecular genetic tools to express genes encoding proteins having larval toxin and growth inhibiting properties will be conducted, including cry toxin genes from Bacillus, and chitinases.
Mosquitoes are responsible for transmission of large number of human pathogens, including those causing malaria, filariasis, and arboviral infections. Abundance and longevity of adult, female mosquitoes (the blood feeding and pathogen transmitting stage) are dependent upon the nutritional and other factors operating in the larval environment, the constraints of which are the focus of the research here.
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