E. J. DIETRICK, Rincon Insectary, Ventura, California
Accepted for publication January 16, 1961. Partial cost of publication of this paper
was met by the author.
JOURNAL OF Economic Entomology Vol. 54, No. 2, April, 1961 pp. 394-395
The principal objection to the use of the portable air suction machine (Dietrick et al.
1959, 1960) for sampling insect populations in alfalfa fields has been the weight of the
motor fan unit. Hence, the design and manufacture of a light weight portable motor fan
became desirable (fig. 1, W). This has been accomplished by the author in cooperation with
the Master Fan Corporation of Los Angeles, California. The backpack mounting enables the
operator to have both hands free to manipulate the collecting attachments, thus making it
possible for one person to take samples.
Fig. 1 -A new backpack vacuum insect collector: W, various attachments;
X, square foot area sampler; Y adapter hose for increased suction; Z, vacuum insect net.
The overall dimensions of the new backpack motor fan unit are 15 X 15 X 24 inches and
the weight is 27 pounds. The air flow capacity is the same as was obtained by the heavier
machine (Dietrick et al. 1959). A single cylinder, air-cooled, two-cycle gasoline engine
of the type used on lawn mowers is used to turn the light weight fan. The air intake is
through an 8-inch opening from the top and the exhaust is straight out the back. The motor
is mounted below the fan, thus keeping the center of gravity low for easy balance. The
carburetor is of the non-float type which feeds gasoline no matter what the position of
the motor is.
A flexible air duct connects the various collecting attachments to the fan intake and
is a 5-foot piece of 8-inch diameter, wire-ribbed, canvas air duct. The portion of the air
duct which holds the organdie insect collection bag is formed by a fiber glass cylinder.
This 13.5-inch diameter by 11-inch cylinder is connected to the flexible air duct by a
tapering section of plastic-coated nylon. This 18-inch long, nylon section is held open by
wire ribs and two metal supports. The entire air duct folds accordion-like into a
convenient package for transport.
There are many possible collecting attachments which may be operated from the basic
motor fan and flexible air duct unit. The insects are sieved by the organdie bag as near
to the collecting head as possible. This bag needs to be large enough and tapered to allow
for good air flow after it begins to fill with insects and duff. This arrangement enables
the insects to be screened without damage to them.
The square-foot area collecting head is copied after the one used in the previous
reference except that it is made from light weight fiber glass material. This cylinder
fits inside the attached cylinder on the end of the air duct, and holds the collecting bag
in place. The open end of this collecting head cylinder is ringed with small,
screen-covered openings. When the collecting head is pressed against the ground, these
openings allow for a continuous flow of air which is necessary to gather the insects
efficiently and to hold them and the duff firmly in the organdie bag, regardless of the
position of the collecting head (fig. 1, X).
The size of the openings of these unconnected cylinders can vary with the size of the
plant or the purpose of the collection. Fiberglass cones can expand or decrease the area
covered by the open end of the collecting head cylinder. Row crops may be sampled with a
long narrow collecting head or by squeezing the fiber glass cylinder to fit the row of
plants. Smaller flexible hoses may be adapted to fit inside the collecting bag (fig. 1,
Y). Cotton has been sampled by placing cylinders of different size over the plants,
increasing the height of the cylinders as the plants grow.
There are limits of plant size where this method of completely covering the plants
becomes impractical. A handle may be connected to the collecting cylinder and the unit may
he used like a sweep net (fig. 1, Z). This vacuum insect net may be used to brush over the
foliage, or placed over entire branches of larger plants or limbs of trees. Citrus, pear,
and oak trees have been sampled in this manner.
The backpack insect collector has been used extensively during 1960 for collecting and
studying beneficial insects on cotton. It has proved to be most useful in studying and
sampling the tiny egg parasites, Trichogrammatidae, and the Mymaridae. A larger proportion
of the immature stages, small caterpillars and even eggs, are gathered, giving earlier
warning of needed control measures, allowing time to make application before the worms are
large enough to cause economic damage. A more complete and accurate estimate of the total
insect population may be obtained from samples gathered by this method (Dietrick &
Schlinger 1960). The modifications described here make the equipment more flexible and
useful in sampling insects and other arthropods on many crops, and could very well become
a useful tool for the collection and detection of new species in survey work (foreign or
domestic) and in quarantine work.