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Counting the Mites 
For counting the specimens a thin transparent celluloid card is 
inserted between the glass slides and the metal clip. This counting 
card (fig. 8) has four white areas 1/4 or 1/8 inch wide and 41/4 inches 
long, so arranged that they will coincide with the approximate centers 
of the four slides when the card is shoved tightly against the retaining 
stops. The white areas may be made with plastic paint or plastic tape. 
Counting is done with reflected light from an ordinary microscope lamp. 
When a card containing 1/4-inch strips is used, each slide represents 
a sample area of 1.06 square inches, and each fork 4.25 square inches 
(approximately 1 inch of planted row). When a 1/8-inch strip is used, 
one-half these areas are represented. No statistical differences were 
observed between counts made with the two areas. Other types of 
counting patterns may be used, such as four 1/4- by 1-inch areas placed 
one above the other in the center or run diagonally across the card. 
The differences between such patterns did not exceed 4 percent. 
If the number of mites present over the counting area is not suf- 
ficient for an adequate count, the entire slide may be examined under 
lower power. Furthermore, where low populations occur or slide- 
carrying space is limited, as on an extended survey, a composite sample 
may be taken on a single set of four slides, and so labeled. 
After the counts have been completed, the slides are placed ina 
cylindrical wire screen basket and submerged in a solvent (fig. 9) where 
they are agitated a few times and then allowed to soak to dissolve the 
mineral oil and vaseline. The clean slides may then be wiped with a rag 
or placed in hot water and spread out on a rack to dry. If cleaner slides 
are desired, they may be agitated in hot, soapy water after being removed 
from the solvent, and then rinsed in hot water. The metal clips are cleaned 
by wiping with a rag moistened with solvent, or soaking in the solvent and 
then wiping. 
Other Uses of the Sampling Fork 
The sampling fork was found to be very satisfactory for estimating 
populations of the spotted alfalfa aphid and various species of thrips 
and other insects found in alfalfa fields. However, the optimum pro- 
portion of mineral oil and vaseline varies with the insects being col- 
lected. For example, a 5 to 1 mixture retained practically all the 
aphids, whereas a few were able to escape when 3 parts of mineral 
oil to 1 part of vaseline was used. When several species are present, 
the proportion should be the one that will catch those insects most 
likely to escape. By this procedure the fork should be practicable for 
Sampling any small athropod attacking small grains that has a tendency 
to fall when the plant is disturbed. 
