Influence of Mosquito Larvae on Bacterial Species Diversity and Abundance, and on the Oviposition Response of Gravid Aedes aegypti (Diptera: Culicidae)
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Date
2007-08-08
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Abstract
The primary objectives of our study were to determine whether larval Aedes aegypti alter the bacterial community landscape of laboratory microcosms containing white oak (Quercus alba) leaf infusion (OLI) and to evaluate the degree to which a larval-altered bacterial community influences the olfactory⁄oviposition response of gravid Ae. aegypti. We found that the feeding activity of Aedes aegypti larvae influenced the production dynamics of bacterial food sources. Abundance (cells⁄ml of infusion) of total bacteria (culturable and unculturable species) declined from 8 to 28 d after addition of larvae while abundances of culturable bacteria were largely unaffected by the presence of larvae over a 32-d period. On average, abundance of culturable bacteria accounted for only 2.5% of the abundance of total bacteria in oak leaf microcosms, which suggests that larvae primarily fed on unculturable bacteria. Bacterial community structure for microcosms with and without larvae was profiled with denaturing gradient gel electrophoresis (DGGE) using PCR-amplified 16S ribosomal DNA fragments from extracted total genomic DNA. Analysis of matrix distance coefficients between DGGE profiles using non-metric multi-dimensional scaling demonstrated a larval effect on the bacterial community structure beginning on days 12 or 16 to the end of the experiment (day 32). Additionally, we discovered that over consecutive days, particularly prominent DGGE bands (= bacterial operational taxonomic units) which had appeared in profiles of larval microcosms, were either absent or found at proportionately lower intensities in corresponding profiles from microcosms in which larvae had been absent and vice versa. Such findings provide evidence that mosquito larvae alter the bacterial community structure in laboratory microcosms.
To determine whether alteration of the bacterial community structure in OLI by mosquito larvae influenced the olfactory/oviposition response of gravid mosquitoes, we used a binary bioassay to evaluate the attractant/repellent and stimulant⁄deterrent properties of OLI which contained larvae. Each experimental replicate produced a different olfactory⁄oviposition response pattern over the 32 d of the experiment, indicating that larval alteration of the bacterial community structure had no consistent effect on the olfactory/oviposition response of gravid adults. However, for some experimental replicates, the occurrence of some DGGE gel bands or band patterns was associated with an enhanced oviposition response.
Laboratory experiments were also carried out to investigate the fitness of larval cohorts of Ae. albopictus (Skuse) and Ae. aegypti L. in microcosms containing white oak leaves as a source of detritus. Some microcosms contained whole leaves while leaf particulates were added to other microcosms to simulate the activity of leaf-shredding arthropods in a detritus processing chain. Larval performance variables (larval survival and development time, and adult emergence) in these microcosms were separately evaluated for both mosquito species in factorial experiments involving combinations of larval density (0.5 and 1.0 larvae per mL) and leaf biomass (4.2 and 16.8 g⁄L). Ae. albopictus exhibited superior larval fitness relative to Ae. aegypti at each level of larval density and leaf biomass and for each leaf condition evaluated. Ae. albopictus and Ae. aegypti responded differently to leaf condition, which suggests that processing chain interactions between these species and top-level consumers would vary in nature.
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Keywords
DGGE, bacteria, Aedes aegypti, oviposition
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Degree
PhD
Discipline
Entomology
