8 research outputs found
Habitat availability mediates chironomid density-dependent oviposition
Abstract Knowledge of density-dependent processes and how they are mediated by environmental factors is critically important for understanding population and community ecology of insects, as well as for mitigating harmful insect-borne diseases. Here, we tested whether the oviposition of chironomids (Diptera: Chironomidae; non-biting midges), known to carry the Cholera pathogen Vibrio cholerae, is density dependent and if it is mediated by habitat availability. We used two multiple choice experiments in habitat-limited and habitat-unlimited environments and performed isodar analysis on counts of egg batches after controlling the polarization of light reflected from the habitats, which is known to affect their attractiveness to ovipositing chironomids. We found that, when habitats are limited, egg batch isodars indicate that chironomid selection is density dependent. Although a greater number of individuals selected to oviposit in highly polarized sites, oviposition was also common in sites with low polarization. When habitats are unlimited, chironomid selection is either weakly density dependent, or completely density independent. Chironomids oviposit to a very large extent in sites with high level of polarization, oviposit to a small extent in sites with medium level of polarization, and almost completely disregard unpolarized sites. We suggest that ovipositing females consider the availability of habitats in their surroundings when they choose an oviposition site. When high quality habitats are scarce, more females opt to breed in low quality sites. These findings may be used to limit the spread of Cholera by controlling the habitats available for chironomid oviposition
Aerosol particle chemical characteristics measured from aircraft in the lower troposphere during ACE-2
Tellus (ACE-2 Special Issue), 52B, 185-200.During the Aerosol Characterization Experiment (ACE-2), filter samples were collected aboard
the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Pelican aircraft
near Tenerife in June and July of 1997. The flights included constant altitude measurements in
the boundary layer as well as profiles up to 3800 m providing detailed chemical information
about the composition of the aerosol distribution in the lower troposphere. Three cases with
different air mass origins — clean marine air, anthropogenically-influenced air from the
European continent, and dust-laden air from the Sahara — were identified. The samples were
analyzed by ion chromatography (IC) for ionic species, by combined thermal and optical
analysis (TOA) for organic carbon, and by total reflection X-ray fluorescence (TXRF) for
elemental composition. Particle composition and size distributions for the range of air masses
encountered illustrate links in the chemical and microphysical characteristics of aerosol from
different sources. Clean marine air masses were characterized by low particle number and mass
concentrations with no detectable metals, while anthropogenically-influenced and dust-laden
air had high number, mass, and trace metal concentrations. Anthropogenic sources were characterized
by high concentrations of submicron particles and some Fe and Cu, whereas dust particle
loadings included a significant mass of micron-sized particles and significant loadings of Fe, in
addition to small amounts of Mn, Cu, and Ni. These results showed similar tracers for air mass
origin as those found in other measurements of oceanic and continental air masses. Aerosol
optical properties were estimated with a simplified model of the aerosol based on the measured
compositions. The real and imaginary refractive indices and single scattering albedos differed
significantly among the three types of aerosol measured, with clean marine aerosol properties
showing the least absorption and dust-containing aerosols showing the most. There were only
small differences in optical properties for the two different cases of clean marine aerosol, but
some significant differences between the two dust cases. Since measurement uncertainties affect
these calculations, we studied the type of mixing and the fraction of absorbing species and
found the calculation was sensitive to these variations only for the dust-containing aerosol case,
probably due to the small amount of water present. While the optical properties varied little with composition for clean marine and anthropogenically-influenced cases, they showed a strong
dependence on variations in particle composition and mixing state for the dust-containing cases