December 1951 ET-297
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
A METHOD FOR TESTING AEROSOLS AGAINST COCKROACHES
By J. H. Fales, 0. F. Bodenstein, and P. G. Piquett
Division of Stored Product Insect Investigations
At the Beltsville, Md., laboratories cockroaches have been used as
test insects in the development of the liquefied-gas method of propelling
insecticides as aerosols. In the early work no special techniques were
used, the roaches being freed in large rooms in practical-type tests or
sometimes confined in screened cages. In 1945 a technique was developed
by which German cockroaches confined in small crystallizing dishes
were exposed on the floor of a Peet-Grady chamber. In July 1946 an
improved method was developed which has been used successfully since
that time, and which is described herein. The results obtained with a
standard aerosol against four species of cockroaches are also shown.
The insects are exposed to the aerosol while confined in an open pen
on the floor of a Peet-Grady chamber. After 30 minutes they are trans-
ferred to clean holding cages and provided with food and water. Mortality
counts are taken on the first, third, and fifth days after the exposure.
Equipment and Method
A standard Peet-Grady chamber 6 by 6 by 6 feet is used. The walls,
ceiling, and floor are permanently covered with heavy paper to prevent
contamination with residues due to excessive dosages. The pen is a
wooden frame 30 inches square (i.d.) lined with glass (fig. 1). It is made of
pieces of wood 3 inches wide and 1 1/4 inches thick, and lined with double-
weight pieces of glass 4 inches wide and 30 1/8 inches long. One end of
each piece of glass overlaps that of the adjacent piece and fits into a
1/2-inch groove in the corner of the wooden frame (fig. 2). The frame is
strengthened on the outside by two 8-inch angle irons at opposite corners.
Before a test is made, a piece of gray bogus paper approximately
40 inches square is put in the center of the floor of the chamber. The
pen is placed on this paper with the corners pointing toward the center
of the chamber walls. The pieces of glass are thinly coated with mineral
oil to confine the insects.
For each test 20 roaches of a given species and sex are placed in the
pen. The chamber is closed, and the required amount of aerosol is dis-
pensed into it with a constantly waving motion from an aerosol container
or from the pressure test-tube type of laboratory dispenser, which
delivers calibrated dosages. At the end of the exposure the chamber is
ventilated and the insects are transferred to recovery cages. The glass
lining of the pen and the square of paper beneath it are replaced and the
chamber is ready for another test.
Determination of Exposure Time
The best time of exposure was determined in tests with large nymphs
and adult females of the American cockroach, using a pyrethrum-sesame
oil aerosol. The insects were exposed for 15, 30, or 45 minutes, some
being introduced at the time the aerosol was released and others after
15 or 30 minutes.
Table 1 shows that a 30-minute exposure was satisfactory and that
any aerosol remaining in the air after that time was ineffective. A 15-
minute exposure was too short.
Table 1. --Effect of exposure time on the toxicity of a pyrethrum-sesame
oil aerosol to the American cockroach
Percent mortality in--
Exposure (minutes) = ........
1 day .3 days 5 days 7 days
First 15 0 5 23 23
First 30 0 42 61 61
First 45 11 47 69 69
15th to 45th 0 5 17 20
30th to 45th 0 0 0 0
First 15 0 6 18 18
First 30 0 35 57 57
First 45 0 39 48 51
The importance of the time between exposure and the taking of mortality
counts has been commented on by various workers.
In the early work mortality counts were taken daily for 10 days. Later
the final counts with American cockroaches were made after 7 days and
then after only 5 days. With German cockroaches 4-day counts were
found to be satisfactory.
Table 1 shows the same mortalities of American roaches at the 5-
and 7-day counts and marked differences between the 3- and 5-day counts.
In 122 previous tests on American cockroaches with 19 aerosol formulas,
the 5- and 7-day counts of large nymphs and adult females combined
showed average kills of 79 and 84 percent, respectively. For the method
described here counts are made after 1, 3, and 5 days regardless of the
species being tested.
Knock-down counts are unreliable in roach testing.
Resistance of Cockroaches to a Standard Aerosol
The resistance of four species of cockroaches- -the American cock-
roach (Periplaneta americana (L.)), the German cockroach (Blattella
germanica (L.)), the oriental cockroach (Blatta orientalis L.), and the
brown-banded cockroach (Supella supellectilium (Serv.))--to a standard
aerosol was determined. The Tentative Official Test Aerosol of the
Chemical Specialties Manufacturers' Association was used. This aerosol
contains 2 percent of pyrethrum extract (pyrethrins 20 percent), 2 per-
cent of DDT, 11 percent of petroleum distillates, and 85 percent of
Freon 11 and 12 (1:1). The aerosol was released at dosages of 5, 10,
and 20 grams per chamber.
Figure 3 shows that the oriental and German cockroaches were about
equally resistant, and that both were considerably more resistant than
the American and the brown-banded cockroaches, the latter being the
least resistant. It also confirms previous findings that the adult female
is more resistant than the male, and that the nymphal stage is the most
resistant. Nymphs of the German cockroach were not tried in these
tests, but McGovran and Fales (1) found that these nymphs were not so
resistant as the adult females. The nymphs of the American cockroach
show little difference in resistance between sexes, which is not true in
the adult stage.
The data obtained should be especially useful to persons using roaches
to test low-pressure aerosols by the method described. The dosages
required to kill any stage of the four species used in these studies may
be readily determined. For nymphs of the oriental cockroach a dosage
well in excess of 20 grams would be necessary to obtain medium kills.
Adult males of the American and brown-banded cockroaches showed
extreme lack of resistance to 1.25 and 2.50 grams per chamber. After
5 days 95 percent of the American and 70 percent of the brown-banded
cockroaches were killed by the lower dosage and all the roaches of both
species were killed by the higher dosage.
Dosage Adjustment for Use in Chambers of Different Sizes
Dosages for testing roaches by this method in spaces smaller or
larger than a Peet-Grady chamber are easily determined. The dosage
to use on a given insect and stage, based on the results given in figure 3,
is in direct proportion to the ratio between the area of the floor of the
room and that of a Peet-Grady chamber.
(1) McGovran, E. R., and Fales, J. H.
1942. Roach testing. Soap and Sanit. Chem. 18(3): 101, 103,
105, 107, 117.
Figure 1. --Roach-testing pen.
Figure 2. --Detail of corner construction of roach-
Percent mortality II 3 126t
0 0 CI 0 0 0 0 0 0 0
-- -- S - a -- a
(Oriental-- not sexed)
(Oriental not sexed)
Ameri can female
--- --- -__- -- - a a -
-J(Oriental not sexed)