4.2.5. Sub-sampling mites to count on a bottom board
This method is useful when a high number of mites have to be counted on the board. However, it provides reliable counts for all mite densities on the board. If more than 1,000 mites are present, it is sufficient to count 22 % of the cells to obtain a highly reliable figure (Ostiguy and Sammataro, 2000).
Material needed: a grid with 2-cm cells printed onto a floor board or sheet fitting the size of the board.
Note: make sure the hives are inaccessible to ants or use a sticky board.
1. Cells are grouped into blocks of nine.
2. Three cells per block are randomly selected and greyed (10 % shade) to indicate the cells in which mites are to be counted.
3. The number of mites in the shaded squares are counted.
4. The total number of mites is then divided by the number of cells counted and multiplied by the total number of cells on the board.
5. The total number of mites is divided by the number of days the board was under the hive to obtain the mite fall per day.
Pros: can be more accurate than exhaustive counts when mite fall is high.
Cons: need to design/build/buy the checkered board.