A special chamber for testing insecticidal sprays


Material Information

A special chamber for testing insecticidal sprays
Physical Description:
Lindquist, A. W ( Arthur William ), 1903-
Madden, A. H ( Archie Hugh ), 1904-
United States -- Bureau of Entomology and Plant Quarantine
U.S. Dept. of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine (Washington, D.C )
Publication Date:

Record Information

Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 30360448
oclc - 782959594
System ID:

Full Text
July 1946 B-9

United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine


By Arthur W. Lindquist and A. H. Madden
Division of Insects Affecting Man and Animals

A common method of testing fine-mist sprays against houseflies
and mosquitoes is to expose the free-flying insects in a Peet-
Grady chamber. lihen using this method, however, it is necessary
to wash or cover the interior of the chamber after each test to
prevent the insects from contacting surfaces bearing a deposit of
insecticide from previous tests. This is particularly important with
materials such as DDT, the residues of which have an insecticidal
effect. To overcome this difficulty a special spray chamber was
designed at the Orlando, Fla., laboratory of this Bureau in which
insects were exposed in small screen-wire cages by a swinging pendulum
method to a fine mist of insecticides. This method has been used
satisfactorily since the early part of 1944.

Description of Chamber

The chamber is constructed of 1/4-inch plywood placed over a
light frame (fig. 1). The inside dimensions are 5 by 5 by 4 feet,
giving a capacity of 100 cubic feet. A spray aperture (A), 3
inches in diameter, is located in the center of the front. This
aperture is closed by a swinging cover (B) when not in use. An
opening in the top, 4 by 131 inches, wiTh a tight cover (C), pro-
vides a means of introducing the insects into the chamber.- Obser-
vation windows (D) may be fitted into the front and rear of the
chamber if desirable.

An exhaust unit, consisting of a 12-inch electric fan mounted
inside a wooden conduit 13 5/8 inches square, is fixed at the rear
of the chamber. The conduit leads to the outside of the building,
and the end attached to the chamber is equipped with a closely
fitting slide. The fan, which operates at full speed, is capable
of moving 900 cubic feet of air per minute. A door (E) at one

This work was conducted under a transfer of funds, recommended
by the Committee on Medical Research, from the Office of Scientific
Research and Development to the Bureau of Entomology and Plant

JUL 2 4 1946


side of the ohaber permits clean air to be drawn in from the test
room as the contaminated air is exhausted.

T sprayer consists of a DeVilbiss hand-controllpd paint nozzle
(FIV perated by an eleotri6 compressor (G) at a pressure of 18
pous per square inch. This equipment produces particles with an
average diameter of approximately 18 microns when the nozzle is adjusted
to spray the finest possible mist.

The exhaust fan and compressor motor operating the sprayer are
controlled by switches mounted conveniently outside of the chamber.

A wooden pendulum (H), 1W feet long and constructed from 1-by
2-inch stock, is used in-exposing the insects. The pendulum swings
freely in the cover at the top of the chamber. Two cylindrical
cages, 7J inches high and 2 3/4 inches in diameter, and made of
16-mesh screen wire, are fixed to the end of the pendulum arm by
means of metal trouser clips. The upper clips should be spread so
that they will not grasp the tops of the cages too tightly and pull
them off when the cages are being fastened or removed. Exposing
the isecots in these cages prevents them from coming in contact
with the inner surfaces of the cabinet. The pendulum prevents the
cag-es from hitting the sides of the chamber, but permits the lower
ends of the cages to pass through the center of the chamber as the
pendulum is being operated. A short ladder (I) enables the operator
to reach the top of the chamber.

Testing Procedure

The spray is discharged into the chamber and the cover of the
spray aperture is then swung into place. After a given settling
period, the pendulum, with the exposure cages attached, is inserted
through the opening in the top of the chamber. The pendulum is
swung moderately during exposure to simulate natural flight and to
aid in the passage of spray particles through the wire mesh of the
cages. Following exposure the insects are transferred to clean
cages for knock-down and mortality counts.

Between tests the spray nozzle is washed with acetone and the
,hamber is aired. In airing, the fan is started, the slide pulled,
a xu the door opened. All the contaminated air can be removed from
th Jismber in 2 to 3 minutes. This time limit has been established
by exposing houseflies in the testing chamber for 1 hour following
vsx~ous periods of airing. If two chambers are used, one can be
:ing while a test is in progress in the other.


Since the necessary exposure period for mosquitoes is much shorter
than that for houseflies, a test against both insects may be completed
with one spraying. After a settling period of 10 to 15 seconds the
mosquitoes are exposed for 10 seconds or more, depending upon the
dosage. The houseflies are then exposed before too long a settling
period (usually 30 seconds) has elapsed. The dosage and the exposure
period must be adjusted, as in other methods of testing, to keep
knock-down and mortality within the proper limits for making comparisons.

When knock-down records are completed, the insects are fed and
watered by placing a drop of honey and a bit of water-soaked cotton
on the outside of each cage. The cages are placed in cardboard
cartons of convenient size and stored at a constant temperature until
the 24-hour mortality counts are made. When all records are completed,
the remaining live insects are killed by placing the cages in an
electric oven for a few minutes. This makes it possible to determine
the total number per cage and to calculate mortality.

The screen-wire cages are washed in white gasoline and acetone
after each test, and the holding cages are washed biweekly. Placing
a tight-fitting white cardboard disk in the solid bottom of each
holding cage facilitates the making of knock-down and mortality counts.


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