Biomedical subjects

P E Dale

Publications and source records attributed to P E Dale.

7 recordsLinked to original sources

PubMed1999

Eggshell sampling: quantitative or qualitative data?

This research evaluated the use of qualitative presence/absence data compared with quantitative real number counts of Aedes vigilax eggshell data to obtain information on the spatial distribution of eggshells in several salt marsh vegetation types. Eggshells were extracted by subsampling and flotation, a method that does not recover all eggshells. The results of the analysis of presence/absence data were compared with those of real numbers. The general conclusions were similar by either method, suggesting that presence/absence data may be sufficient to rapidly determine eggshell distribution patterns.

Aedes↗

PubMed1999

Acid sulfate soils in intertidal mosquito breeding habitats and implications for habitat modification.

Public concern about the use of chemicals for mosquito control in coastal Australia has lead to the development of physical habitat modification methods that aim to reduce mosquito populations to acceptable levels. Habitat modification methods include runnels (depth < 0.30 m) and ditches (depth > 0.50 m). During excavation for habitat modification, a risk of exposure of acid sulfate soils may exist. Acid sulfate soils are soils that contain iron sulfides, in particular pyrite (FeS2), and produce sulfuric acid when exposed to air. These soils occur predominantly in coastal lowland areas that are also prime mosquito breeding habitats. The paper discusses the problem and illustrates the application of survey methods that facilitate wise decision making and management of intertidal wetlands.

Australia↗

PubMed1998

A method for assessing the effects of runneling on salt marsh grapsid crab populations.

Runneling, a type of habitat modification using shallow channels, is an effective method for controlling mosquitoes that breed in intertidal salt marshes. Grapsid crab populations were studied to assess the environmental effects of runneling on nontarget species. Pitfall traps provided a means of monitoring crab distribution and relative abundance at Coomera Island in southeastern Queensland. The study indicated that although runneling does not have a significant effect on the total number of crabs, it may have a significant impact on species distribution. Significantly greater numbers of Parasesarma erythrodactyla were found at the runneled site. In contrast, Helograpsus haswellianus was more abundant at the unrunneled control site. Associations were also found between species abundance, distance from the tidal inlet, and vegetation type. Helograpsus haswellianus was associated with mixed vegetation, whereas Parasesarma erythrodactyla was associated with tall, dense salt marsh couch. No correlation was found between the number of crab burrows present at the study site and the number of crabs caught in the traps. However, the runneled site had approximately twice the number of crab burrows of the unrunneled control site. These results were consistent for 3 consecutive monthly sampling periods. The method has proven suitable for further studies on the long-term environmental impact of runneling.

Animals↗

PubMed1998

An overview of remote sensing and GIS for surveillance of mosquito vector habitats and risk assessment.

This paper provides a brief nontechnical overview of the use of remote sensing to achieve multiple objectives, focusing on mosquito management. It also shows how Geographic Information Systems, combined with remote sensing analysis, have the potential to assist in minimizing disease risk. Examples are used from subtropical Queensland, Australia, where the salt marsh mosquito, Aedes vigilax, and the freshwater species, Culex annulirostris, are vectors of human arbovirus diseases such as Ross River and Barmah Forest virus disease. Culex annulirostris is also implicated in the transmission of Japanese Encephalitis. Mapping the breeding habitats of the species facilitates assessment of the risk of contracting the diseases and also assists in control of the vectors. First, it considers a simple risk model that is applied to data for the city of Brisbane in southeast Queensland. This is then linked to computer-aided analysis of remotely sensed data to map potential ephemeral freshwater breeding sites of Cx. annulirostris. This has the potential to guide control at critical times, for example after heavy summer rainfall or when there is an outbreak of Ross River virus disease. Second, the use of color infrared aerial photography is used to identify the specific parts of the salt marsh in which larvae and eggs of Ae. vigilax are found. Finally, we explore novel ways to map the detailed pattern of water under mangrove forest canopy to identify where mosquitoes are breeding and as an aid to planning modification. For each we discuss the limitations and advantages and the possibilities for combining methods and/or using a single method for multiple objectives.

Animals↗

PubMed1996

Culex annulirostris breeding sites in urban areas: using remote sensing and digital image analysis to develop a rapid predictor of potential breeding areas.

A rapid technique is being developed and assessed to identify urban breeding sites of Culex annulirostris, which is a vector of an arbovirus (Ross River virus). Field survey and laboratory identification were used to identify breeding sites for the species. Ephemeral sites became the focus of the research and other mosquito species were recorded. The sites were located on digitized images of 1: 30,000 color aerial photographs. Training sites were used to create "themes" for the main ephemeral breeding sites and the MicroBRIAN image processing package was used to map the themes to each image. The accuracy and completeness of identification were evaluated with reference to the original field site identification and by further field checks. The accuracy was 87% and the completeness was 75%.

Animals↗

PubMed1993

Runnelling to control saltmarsh mosquitoes: long-term efficacy and environmental impacts.

Aedes vigilax is a problem mosquito species prevalent in subtropical Australian coastal wetlands. We evaluate the long-term impacts of runnelling, an environmentally benign habitat modification method, on mosquitoes and the wetland environment. Runnelling uses shallow channels to enhance flushing of the marsh. The method successfully reduced larval numbers to below nuisance levels for the 6.5 year study period. We did not detect any significant difference in the wetland environment between runnelled and unmodified parts of the study area. However, the spatial extent of the effects may have extended beyond the modified area.

Aedes↗

PubMed1989

The runnelling method of habitat modification: an environment-focused tool for salt marsh mosquito management.

Traditional methods of managing salt marsh mosquitoes focus primarily on maximizing the reduction of mosquito populations, with minimizing environmental impact as a secondary consideration. An environment-oriented approach to salt marsh management for mosquito control, runnelling, is described and compared with other forms of habitat modification such as ditching and Open Marsh Water Management (OMWM). Runnelling alters the salt marsh as little as possible while causing significant reductions in mosquito numbers. The effect of runnelling on the environment was monitored via the following variables: water table level, substrate characteristics (moisture, salinity and pH), vegetation (height and density of each Sporobolus virginicus) and the numbers of mosquito larvae. Runnelling had a statistically significant effect on only two of the seven variables. These were the height of Sporobolus, which increased near runnels, and the number of mosquito larvae, which decreased. The main difference between ditching, OMWM and runnelling lies in the magnitude of the habitat modification. Ditching involves the greatest alteration to the marsh, and runnelling the least. Consequently, runnelling has a smaller effect on the estuarine environment as a whole than does either ditching or OMWM.

Animals↗