User Documentation

Conceptual Overview

The diagram below shows the main components of DyMSiM. Vector habitat (water available) determines the resources available for egg laying and larval development. It enters the system through precipitation, irrigation, and as a function of specified land cover. Water exits the system via soil infiltration and evaporation. Temperature impacts the evaporation rate of water, as well as governing the development of the mosquito throughout its life cycle.

From: Morin C and Comrie A C, 2010. Modeled response of the West Nile virus vector Culex quinquefasciatus to changing climate using the Dynamic Mosquito Simulation Model. International Journal of Biometerology 54, 517-529, doi:10.1007/s00484-010-0349-6.

Model Input

DyMSiM requires the input of daily temperature (C°), precipitation (cm), and hours of daylight data, as well as the percentages of permeable and impermeable surface cover and permanent water. Optional inputs are container depth, irrigation, and the infiltration rate of the permeable surface cover. This user documentation will explain to to enter this information in DyMSiM.

Importing Data

A simple way to import your data into the model is by preparing the data in an Excel spreadsheet, and linking that sheet to STELLA. The process for doing this is described here. Should you have trouble inputting your data this way or choose not to use this method, and alternative option is described in the next section.

Preparing your data series in Excel

Temperature, precipitation, hours of daylight, and actual mosquito data for a time series can all be prepared in Micrsoft Excel and imported into DyMSiM. Data orientation can be in row or column form, but Row/Column headings must match exactly the names of the corresponding graphical functions in DyMSiM (i.e. Temperature, Precipitation, Hours Daylight, Real). Because STELLA will only import data with headings that match, it is not a problem if you have additional columns/rows of data stored in the same sheet that you do not intend to import into DyMSiM.

Linking Excel data with DyMSiM

• • Select Edit > Import Data

  • In the box that opens, specify which Import Type you would like

  • Under Import Data Source use the Browse button to select the excel file

  • Under Data Orientation, select the excel sheet’s orientation format

  • Select OK- a dialogue box will appear when data has been successfully imported (note this may take several minutes if you are importing a large amount of data)*

*If you have trouble linking the spreadsheet this way, select Edit > Manage Persistent Links to make sure there is not an existing spreadsheet already linked. If there is, the existing link will need to be deleted before creating a new one. If you are still unable to import your data this way, an alternate method is described below.

Alternate method for entering data

If you cannot get STELLA to properly link with your Excel file, or do not have access to Excel, the procedures described below provide an alternate explanation for importing time series data.

• • Open the Temperature graphical function by double-clicking on it

  • In the window that opens, specify the number of days (Data Points) you will be entering.

  • Enter a “1” as the minimum value for the X-axis, and your last data point as the maximum X-axis value.

  • Highlight all the existing values in the Temperature column and select Edit > Cut (note that the values will not physically be cut from the screen).

  • Select and Copy your list of temperature values from your file, and paste them under the Temperature column.

  • Click OK to return to the model

Use the same steps to enter Precipitation, Hours Daylight, and actual mosquito data if available (Real).

Land-cover information

The amount of suitable habitat for breeding is determined by the amount of water available. This is determined in the model via a series of calculations. The total area is multiplied by the percentage of that landcover classified as permeable, permanent water, and water in containers, resulting in the amount of water available for each of these landcover classifications. The 8cm threshold for breeding is incorporated if the water is deeper, resulting in the actual amount of water available for breeding. The sum of the total water available for breeding on permeable surfaces, as permanent water and in containers reflects the true total value of water available for breeding at the site.

• • Open the Area converter and enter the total area of the location as a fraction of a hectare

  • Open the converter for Percent Permeable, Percent Permanent, and Percent Container converters

  • Enter the percentage of the total area in the ‘Area = …’ box for each land cover class in their respective converters in decimal form

Optional Specifications

Container Height

The “spill” feature allows for precipitated water to flow over the edges of a container once it becomes full, mimicking the actual process. To use this feature, you must input the height of the container. The container height is multiplied by the area of the container, and the difference between this value and the amount of water in the container from precipitation will be “spilled”, therefore preventing the container from holding more water than physically possible.

• • Open the Container Height converter and enter the value you would like to use to represent the height of the container (cm).

Irrigation

In certain locations, irrigation may provide an important breeding source for the mosquito. For example, precipitation in a given location may drop significantly during certain periods of the year, leaving a lack of available breeding water for mosquitoes. However, irrigation ditches may still provide enough habitat that the population remains sustained. Irrigation can be included in the model under two different scenarios: 1. when the temperature is greater than a set temperature threshold, or 2. during a specific period of the year.

• • If you do not wish to use Irrigation in your simulation, leave the value in the IR Index converter at 0.

  • To use Irrigation based on a temperature threshold scheme, enter 1 in the IR Index converter.

    • In the Temp Thresh converter, enter the temperature threshold that will determine when irrigation is used.

  • To use Irrigation based on a certain period of the year, enter 2 in the IR Index converter.

    • Use the Julian Start and Julian Stop converters to specify the Julian Date irrigation should begin and end.

  • The amount of water you want to enter the system via Irrigation (in cm) is entered in the IR Amount converter.

Permeability Rate

By specifying the permeability rate of the soil, water loss that would occur due to soil infiltration can be included. The permeability rate is multiplied by the total area of Permeable water via the Infiltration flow, which acts to remove this water out of the ground water for mosquito breeding.

• • Open the Permeability Rate converter and enter the rate at which water is lost through soil at the location as a percent ex: 80 {percent}

Real Mosquito Count Data

Entering real mosquito count data allows for modeled populations to be compared to actual data for the same time and location, useful for validation purposes.

• • Open the Real graphical function. Enter data following the same instructions for entering Temperature, Precipitation and Hours Daylight data described above. This can be done either manually or via Excel spreadsheet linkage.

Temperature Difference

The Temp converter is specified by the equation Temp = Difference + Temperature. Therefore, the Difference converter allows you to easily offset all temperature values by the same number- for example modeling mosquito populations under varying temperature change scenarios.

• • Open the Difference converter

  • Enter the value by which you would like temperatures to be offset by

    • To decrease temperature values, enter the difference in the form of a negative number

  • Leave value at 0 if you do not wish to use this feature

Ecological Suitability Coefficient

The ecological suitability coefficient specifies the quality of the conditions for immature mosquito growth. A value of 1 reflects ideal conditions, and can be decreased as necessary for assume less favorable conditions. The coefficient is multiplied by the maximum larval/pupae density for survival and the total effective water available to determine the carrying capacity of the system.

• • The default value for this coefficient is set at 1, decrease this value in the Food or Ecological Rating converter if necessary.

Running the model

• Select Run > Run Specs and enter the specifications for the model run.

• Ensure Days is selected under Unit of time

• Specify the length of the simulation by entering this information in the From and To data boxes. This should represent

the number of days in your time series

• Enter a DT value of 1 (because the model runs on daily data).

• Select Euler’s Method as the Integration Method, and Normal as the Run and Interaction Mode

• When you are done setting up the model, click OK. To run the model, select Run > Run

Viewing Results

Results can be viewed in STELLA by inserting a table and/or graph, or by linking STELLA to excel. Please refer to the STELLA help document for additional information on these techniques.

Inserting Tables and Graphs

• • Click on the Graph Pad or Table Pad icon in the tool bar

  • Click anywhere on the STELLA screen to insert the graph or table

  • Double click on the graph icon to open the feature

  • For graphs, double clicking on the X and Y axes allows you to specify what information you would like displayed

  • For tables, you can specify the information by clicking on the column heading

Exporting to Microsoft Excel

Data generated by DyMSiM can be exported to an Excel spreadsheet one time, or each time the model is run by linking it to an Excel file.

• • To set up this connection, select Edit > Export Data