Calculating mite populations using a mite brushing sample. Count mites in the sectors of a mite brushing plate using a dissecting microscope set on the lowest magnification that lets you distinguish twospotted spider mites and predatory mites. Start counting each sector either at the point or the wide end and zig-zag your way to the other end of the sector. Number the sectors as above and count them in numerical order, following the protocol below to decide when to stop counting. Keep separate tallies of twospotted mites and predatory mites. Calculate the total number of motile mites on the plate and divide by the number of leaflets that were brushed to get the average number of mites per leaflet.

Number of sectors counted	Stop counting if number of motile mites is equal to or greater than	To get total number of mites, multiply by
2	9	6
3	12	4
6	25	2
9	38	1.33
12	—	1

Illustration adapted from Integrated Pest Management for Strawberries, 2nd edition. UC ANR Publication 3351.