Overview of STS decisions

The goal of the USDA Forest Service Slow the Spread (STS) project is to reduce the rate of expansion of gypsy moth populations in the US.
The method of STS is to detect isolated colonies beyond the expanding population front and to eradicate (or suppress) them.

This Decision-Support System is designed to help find isolated colonies and to select an appropriate management action. Gypsy moth abundance is evaluated using pheromone traps which look like paper boxes for milk (see picture). This trap is baited with pheromone which is a chemical that is normally produced by gypsy moth females to attract male moths. Male moths enter the trap and die inside. The trap is checked after the flight season is over, and the number of moths inside is an indicator of population abundance in the area.

Pheromone traps are highly sensitive; they can attract male moths that are a mile away. However, most moths that get into the trap originate within 100-200 meters from the trap. In the STS project we use a 2-km grid of traps. If some traps have an unusually high number of moths compared to neighboring traps, then there is a possibility of an isolated colony in this area. Thus, we set a denser grid of traps with 500m intervals. This is called a delineating grid because it not only confirms the existence of a colony but also provides information on its boundary. After delimiting the colony can be treated. The most frequently used treatment agents are a bacterial preparation, Bacillus thuringiensis (Bt), and the synthetic pheromone, disparlure. Neither agent affects vertebrate animals nor humans. Bt may affect other non-target insects but disparlure has no effect on any other organisms. Disparlure disrupts chemical communication between females and males. As a result, females remain unfertilized and lay nonviable eggs.

Actions recommended by the Decision-Support System are:

• where to put delimiting grids of traps and
• what areas to treat.

Data processing

Data submission and processing are performed by qualified personnel only. Thus all forms for starting the analysis are password-protected. Complete data analysis and map generation takes several hours on a very fast computer. The results of analysis are available for general public in this web site.

Viewing maps that show moth counts in traps and STS decisions

To view interpolated moth counts in pheromone traps over large areas go to the home page, make sure that the radio button "Map of STS decisions" is selected, and then click on the color map (at the right side). In the next page that will appear you can select various years and various maps. These maps include: moth counts in individual traps, location of STS project boundaries suggested by the computer (actual boundaries may be a little different), population growth rates, and STS decisions, i.e., areas recommended by the computer for delimiting and treatment. All these maps have resolution of 1 km per pixel.

Additional static layers (that are the same for all years) of these low-resolution maps include elevation, vegetation, and predicted gypsy moth phenology that is based on 30-yr average weather data. The map of moth flight phenology has additional information on dates for placing and removing pheromone traps in various areas (see the legend). There is also a map of traps that were set too late or removed too early (Set/Remove dates).

If you click on the low-resolution map you will get to a medium-resolution map which is 200 m per pixel. In this map you can select a foreground and background of your choice. For example you can see the location of each trap.

The Decision-Support System selects Potential Problem Areas (in short PPA) where isolated colonies of the gypsy moth may be located. On the map, PPAs are outlined with a green thick line. All PPAs are numbered within each state, so the identification number of a PPA is state name + the number. In medium-resolution maps, each PPA is marked with 3 numbers, e.g., 105-5/4, where 105 is the identification number, 5 is the maximum moth counts per trap within this PPA, and 4 is the maximum moth counts per trap in the previous year. Below the map you will find a table of all PPAs in this map. PPA attributes in this table include the size (area), distance from the beginning of the STS action area (action area is the area where isolated colonies are being detected and suppressed), background moth captures in the area outside of the PPA, and other characteristics. Based on these (and some other) attributes, two integrated indices are estimated: the priority index, and the delimiting index (see details here). The priority index shows a possibility of finding a colony and expected population density, whereas the delimiting index shows if the colony is well delimited with traps so that treatment can be applied. Based on these two indices, the Decision-Support System recommends delimiting, treatment, or no action in each PPA. A PPA is marked with a red circle if it is recommended for treatment, and with a green circle if it is recommended for delimiting.

Navigation in medium-resolution maps is simplified by thumbnail maps in the upper left corner. To move to a neighboring area, click on the border of the map. You can also move from one year to another using buttons at the top of the page. The map is divided into six squares that correspond to high-resolution maps. Click on any square and you will see the high-resolution map which has 50 m per pixel.

In high-resolution maps you can see moth counts in every trap. You can also bring up the vegetation layer to see forested areas, rivers, villages and towns. There are two thumbnails in the upper left corner: one shows the location of the area in a bigger region, and the second indicates the location of individual PPAs within the map (this is helpful if you are looking for a specific PPA). Buttons at the top of the page are designed to navigate through years. PPAs are marked with a red or green circle if they are recommended for treatment or delimiting, respectively. The identification number for PPAs is shown in a box so that it is not confused with trap catches. To get to the adjacent area, click on the border of the map. At the bottom of the page you will find the same table with PPA attributes as in medium-resolution maps.

From maps of various resolutions there is a link to the complete table of all PPAs in all states. This table has back links to high-resolution maps with these PPAs. Also you can download a text file with all PPA attributes (this file is tab-delimited and should be viewed with MS Excel). There is a shortcut link from the home page to the table of all PPAs. Just click on the radio button, or select a different year.

Actions recommended by the Decision-Support System are reviewed by people who make actual decisions. In some cases actions are modified by decision-makers. For example, there may be not enough resources to treat all areas recommended by the computer. Then PPAs with a lower priority index may be left untreated. Areas assigned for delimiting and treatment usually differ from areas that were originally selected by the computer. Information about areas selected for delimiting and treatment is loaded back into the computer, and the Decision-Support System updates all maps and draws the actual areas that will be delimited and treated (see medium- and high-resolution maps). In some cases actions may be taken in areas that initially were not selected as PPAs by the Decision-Support System. The computer will assign new identification numbers to these areas and evaluate their characteristics in the same way as with regular PPAs. Then, the computer compares areas that were initially recommended for delimiting and treatment with those areas that were selected by decision-makers. The report is generated and can be accessed from the table of all PPAs. This report indicates all PPAs where management action has been changed and sorts them in the order of importance. Also, comments may be available that explain the reason for changing the action. Comments were implemented in 2001.

Evaluating the success of STS treatments

The second major component of the STS Decision-Support System is used to evaluate the success of treatments. For every treated block the computer estimates an index of treatment success, T, which indicates the degree of reduction in population abundance after treatment.

To get to the table of treatment evaluation, go to the home page, select the radio button "Table of STS treatments", change the year if necessary, and then click on the map at the right for an area of interest. In the table of treatments you can navigate between years and geographic areas using buttons at the top of the page. On the left side there is a link to the map of all treatment blocks for the given geographic area. In this map you can click on any treatment block (shown by a magenta circle) to get to the treatment evaluation page for this block. Another path to this page is to get back to the table of treatments and click on the name of a treatment block.

In a treatment evaluation web page (e.g., this page) you can see major attributes of the treatment block: its acreage, treatment agent, number of treatments, etc. The PPA number in the previous year provides a link to the map of that PPA. There is a detailed high-resolution map (40 m in a pixel) of the treatment block. You can view this map over the background of the vegetation map. Below there are maps of interpolated male moth counts in traps in the year before treatment, in the year of treatment, and in the year after treatment. These maps help to visualize the success of the treatment. If you click on these maps you will get to the high-resolution map described in the previous section. Average moth counts in the treated and control areas (control area is a 24-km neighborhood excluding treatment blocks and 2-km buffer zone adjacent to these blocks) and maximum moth counts in the area treated are shown below these maps for each year. Treatment and control areas are shown with magenta and yellow color in a small map at the bottom of the page. This map helps in troubleshooting if some estimates appear wrong. There is also a thumbnail map that shows the location of the treatment area.

Monitoring the rate of gypsy moth spread

To access the web page with information on rates of gypsy moth spread, click on radio button "Analysis of population spread" in the home page. After you get to the page "Analysis of gypsy moth spread", click on the area of interest to see the table and graphs of the rate of population spread. Besides the rate of spread, the table provides information on the annual rate of population increase and interboundary distance which is the distance between neighboring moth lines drawn at thresholds of 1, 3, 10, 30, 100, and 300 moths/trap. The interboundary distance may be an additional indicator that evaluates the effect of the STS project.