|Mint Root Borer|
|Sampling for Soil Insect Pests: An
Inexpensive Way to Build a Berlese Funnel
Oregon State University Extension Service
Extension Circular 1079
Prepared by Ralph E. Berry, associate professor of Entomology, Glenn Fisher, Extension Entomology specialist, and Elson Shields, former pest management specialist,Oregon State University.
Many soil insects and related organisms are important crop pests. These include garden symphylans, root weevil larvae and adults, white grub larvae, flea beetle larvae, wireworms, clover root borer larvae and adults, sod webworms, mint root borers, and various subterranean cutworms.
pests can be difficult to detect, and a great deal of time and effort is required to
obtain enough samples to get a good estimate of soil pest populations. However, sampling
for these pests can be made easier by using several Berlese funnels. Information on the
life histories and management of these pests can be found in various OSU Extension
publications. Consult the current list of publications available from county Extension
two 5 gallon drums
First, rinse containers well. Remove both ends from
one of the 5-gallon containers. Flatten sharp edges with a hammer. Next, drill two 5/16
inch holes opposite each other, 3/4 inch from the bottom of the drum. A second set of
5/16-inch holes should be drilled 1/2 inch up from the bottom, spaced approximately 90°
from the first set of holes. Insert 1/4 x 12 inch rods through opposite holes to form a
cross support. Using the bottom of the drum as a pattern, cut a circle from the 1/8 inch
screen and fit it into the bottom of the drum above the cross supports. Tie the screen to
the cross supports with wire.
The completely assembled Berlese funnel consists of a
securely mounted sheet metal cone with canning jar and band attached to the cone's narrow
end, a 5gallon drum with the ends removed and wire screen installed over cross supports,
and a half drum with light bulb and socket installed.
A soil and root sample or sod sample about 1 foot
square by 2 to 4 inches deep (6 inches for root weevils and clover root borers) is placed
inside the drum on the wire screen. The lid is placed on the top of the drum, slightly
ajar, to allow moisture to escape from the soil, and the light bulb is turned on. The heat
from the light bulb forces the soil insects out of the sample by drying the soil. These
insects fall through the wire screen and slide down the funnel into the half-pint
collecting jar. After the soil and roots are completely dry, the pests in the collecting
jar can be removed, identified, and counted. Make sure the soil and roots are completely
dry so that no pests remain in the sample.
To estimate populations of soil pests, the sampling
methods must be practical and the estimates of densities must be reliable. For soil insect
pests living in the top 2 to 4 inches of soil, roots, or other plant material, a square
foot sample 4 inches deep is adequate. This method works for root weevils, flea beetles,
clover root borer, mint root borer, sod webworm, and most subterranean cutworms. In other
situations, core samples about 6 inches in diameter, including the plant roots, should be
taken to a depth of about 8 inches to 12 inches for wireworms and symphylans.