A dust delivery tube for laboratory experiments with contact insecticides


Material Information

A dust delivery tube for laboratory experiments with contact insecticides
Physical Description:
Fisher, Robert A
United States -- Bureau of Entomology and Plant Quarantine
U.S. Department of Agriculture, Bureau of Entomology and Plant Quarantine ( Washington, D.C )
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aleph - 030345337
oclc - 781635095
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ET-151 August 1939

United Statc- D_-pi utment of Agriculture
Bureau of Entomolcjy and Plant Quarantine


By Robert A. Fisher,
Division of Truck Crop and Garden Insect Investigations

Laboratory tests with contac+ dusts for the pea weevil (Bruchus
pisorum (L.)), conducted in connection with field-control experiments, have
resulted in the development of a dust-delivery tube which gave more uniform
distribution of duist, and higher kills with :,-aller quantities of dust, than
other types tested.

The apparatus used for this work consists essentially of a bell jar
having a diameter of 9-L inches, a small wooden stand 11 inches square with
a 1-inch hole bored through the center of its top, and a glass delivery tube
for discharging dust into the jar (fig. 1). The delivery tube is connected
to a pressure gauge on a compressed-air line by a 3-foot piece of rubber

The delivery tube originally used had an inside diameter of 7.3
millimeters, with the opening slightly flared. Spirally arranged indenta-
tions along the length of the ti.b- helped to break up dust particles and
distribute them more evenly. Hov-ever, the distribution over the area beneath
the bell jar was not as even as was desirable, apparently because it was
impossible to set the tube exactly perpendicular for each test.

After some experimentation it was found that dust which was discharged
through a tube that had been drawn to a fine tip settled in a more uniform
film within the jar. This tube was made from 7-millimeter glass tubing,
with the inside diameter of the opening about 1.5 millimeters. Care was
taken, when drawing out the tip, to center the opening as nearly as possible.
The tube was bent at right anles, the p1.rpendicular part bearing the
constricted tip being 3j inches long.

1 Formerly junior entomologi-t, Division of Truck Crop and Garden
Insect Investigations, Bureau of E::to!polopy and Plant Quarantine, U. S.
Department of Agriculture. At pre-Pnt assistant entomologist, Department
of Entomology, University of Idaho


The dust reservoir, adopted from the apparatus described by Payne
and Stultz, 2 consisted of a centrifuge tube fitted with a two-hole rubber
stopper. Two glass tubes were fitted into the stopper. One tube, extending
nearly to the bottom of the centrifuge tube, was connected to the air line.
The second, which was flush with the lower surface of the stopper, was
connected to the delivery tube by a short piece of rubber tubing. This
apparatus, with the delivery tube, is shown in figure 2.

When a test is to be made a charge of dust is placed in the dust
reservoir, and the delivery tube is inserted through the hole in the stand,
where it is held in place by a rubber stopper. Fifty weevils, confined in
a small screen cage inverted over a petri dish, are placed on the stand,
together with two pieces of weighed millimeter paper, each measuring 70 by
90 millimeters. The weevils and papers are then covered by the bell jar.
With all the materials thus in place the dust is blown into the jar under a
pressure of 5 pounds per square inch, and allowed to settle on the insects.
Five minutes time is sufficient for practically all the dust to settle.
The weevils are then transferred to a clean cage and placed in a constant-
temperature box for further observation to determine the mortality. The
quantity of dust per unit area settling on the insects is readily determined
by reweighing the millimeter paper. In this manner quantitative determina-
tion of the toxicity of various dust mixtures can be made.

The constricted tube not only gives a more uniform distribution of
dust, but the mortality resulting from the same quantity of dust is greatly
increased. A cube dust in talc, containing 1.00 percent of rotenone, gave a
median lethal dose of about 10 milligrams per 100 square centimeters when
the original open tube was used; with the constricted tube the median lethal
dose was about 5 milligrams per 100 square centimeters. Similar results
were obtained when diatomaceous earth was used as the diluent. The main
reason for this increased mortality apparently lies in the mechanical dis-
tribution of the dust particles. Dust particles discharged from the original
tube have some tendency to cling together. With the constricted tube the
particles are nearly all separated from each other, and so possibly have more
opportunity to come into direct contact with the insect body. This dif-
ference in dust distribution is shown in figures 3 and 4.

It has been demonstrated that the size of the opening of the tube
through which dust is discharged into the bell jar plays an important part
in the type of dust film deposited. This was done by employing the con-
stricted tube, a glass tube of the same diameter as the constricted tube
but without the constricted tip, and the original open tube, all in con-
junction with the centrifuge tube dust reservoir. Microscopic examination
of the dust films showed that the larger the opening the coarser was the
film deposited.

2 Payne, S. H., and H. T. Stultz. 1937. A laboratory apparatus for
determining the relative toxicity of contact dusts. Sixty-seventh Annual
Report of the Entomological Society of Ontario, 1936, pp. 30-33, illus.


Another factor which has some effect on the type of dust film depos-
ited is electrostatic charges on the dust particles. Dust blown from the
original open tube carries little, if any, electrostatic charge. However,
during agitation of the dust in the centrifuge tube the particles become
negatively charged.3 Since all the particles carry like charges they tend
to repel each other and settle in a fine film. This is shown by the fact
that dust films from the open tube used alone are slightly coarser than
films deposited when the open tube is used with the centrifuge tube dust
reservoir.4 From this it appears that both the size of opening of the
delivery tube and the charge received in the dust reservoir have an important
bearing on the efficiency of contact dusts for the pea weevil.

3 Determined by Dr. G. W. Hammar, Department of Physics, University of
Idaho, Moscow, Idaho.
4 Charged dust particles also adhere better to any surface than un-
charged particles, and so undoubtedly stick better to the insects' bodies.

Digitized by the Internet Archive
in 2012 with funding from
University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation


tifr 1, App~atus us" In laboratory futstig eOperlmnts.

^F F-W





Tigure 2. -Details of delivery tube and dust reservoir
used in laboratory experiments.

JK -



Tigure 3. -Photcuicrograph showing the appearance of
dust composed of cube (1% rotenone) in diatomaceous
earth and applied with an open tube.

Figure 4. Photoalorograph showing the appearance of
a dust composed of cube (1% rotenone) in diatomaceous
earth applied with a cozatricted tube.


II 3 1262 08537IIll BtII IIIBI 11011
3 1262 08537 1101

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