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ET-165 November 1940
United States Dspariiiment of Agricultur,.-
Bur?au of Entomology and Plant Qu., r-itine
A MEASURED DROP METHOD OF APPLYING LIQUID I'L'S'TTviDES
By E. R. McGovran, G. L. Phillips, and E. L. .',Tver,
Division of Control Investigationis
The method of applying measured drops of lic-id insecticides
to individual insects has frequently been used. Ntelson et al.l_/
describe a method using micropipettes that. when filled, hold a
test dose for a single housefly. Smith/ uses a cactus spine to
apply small quantities of oil to the spiracles of scale insects.
Woodbury and Barnhart3/ describe a method utili__1i,, a micropipette
that holds sufficient insecticide to treat a number of bedbugs.
The dose for the individual bug is delivered by air pressure.
The apparatus described here is diagraih,.!!:e;1 in figure 1.
A metal hypodermic nee:11e (F) is attached by Dct'.oi. insky cement
to a 0.2-ml. pipette (C), which is subdivided into one-thousandths
of a ml. The upper end of the pipette is attached to glass tubing,
which leads through a stopcock (B) to a reservoir (A) for rinsing
and to a microinjector (G) that will deliver small di ps of liquid.4/
When the hypodermic needle is to be attached to the tip of the
pipette, clogging is prevented by inserting a fine wire through
the needle and into the pipette and leaving it there while the
melted cement is being applied.
I/ Nelson, F. C., H. E. Buc, N. A. Sankowsky, and M. A.
Jernakoff. A new method for evaluating the relative toxicity of a
liquid insecticide. Soap 10 (10): 85, 87, 89, 91, 105, 107. Oct.
2/Smith, Ralph H. Microtechnique method of tesiirng oil in-
secticides on scale insects. Jour. Econ. ELt. 31 (5): 632-633.
3/'Voodbury, E. N., and C. S. Barnhart. Teii,'tive methods for
evaluating liquid household insecticides agair,'t '-,e Germnan cocj:-
roach and the bedbug. Soap 15 (9): 93, 95, 97, :- 101, 103, 105,
107, 113. Sept. 1939.
4/The authors are indebted to C. S. Wilson, of the Bur--au of
Entomology and Plant Qjarantine, for suggestion/ the -i-. of this type
* / _-')-,-
Figure 2 is a photograph of the apparatus in operation.
The glass tube is joined to the microinjector with beeswax. Joints
in the glass tubing and where the pipette joins the glass tubing
are mnare of rubber tubing covered -over and sealed with beeswax.
The glass is brought together as close as possible inside the rubber
tubing. This method makes a tight seal and also allows slight
flexibility, which DeKhotinsky cement does not permit. The entire
system must be entirely free of leaks to operate satisfactorily.
The entire apparatus is securely fastened to a wooden base by wood
screws, as shown in figure 2.
The whole apparatus is completely filled with distilled
water before any insecticide is drawn into the pipette. If ap-
preciable amounts of air are left in the microinjector or the
tube connecting it with the pipette, the delivery of insecticide
at the point of the needle will not be at a uniform rate. When
the microinjector crank is turned to force the insecticide out of
the needle, any considerable volume of air (1 or more ml.) will
be compressed by the surface tension of the liquid across the very
small opening in the tip of the needle. When this pressure becomes
great enough to stretch this surface, a drop is formed on the tip
of the needle. However, the slightly compressed air in the ap-
paratus expands as much as possible at this time, and this expansion
often results in a larger drop of insecticide forming on the tip of
the needle than is desired. Also, owing to further expansion of the
air, additional material may come out of the pipette when the drop
is removed. For this reason distilled water, or some other rela-
tively noncompressible material that will not appreciably affect
the toxicity of the insecticide, should be used in the microinjector
and the tube connecting it with the pipette.
Operation of Apparatus
After the apparatus below the stopcock has been filled with
distilled water the microinjector plunger is screwed completely
in. Turning the crank shown in figures 1 and 2 in a clockwise
direction moves it to the left until it rests against the body of
the injector. Any water on the tip of the needle is wiped off.
The microinjector plunger is then withdrawn slightly by making
two turns of the crank in a counterclockwise direction. This
allows a small amount of air to enter the needle. The tip of the
needle is then submerged in the insecticide, and the plunger -is
withdrawn by rotating the crank until the desired quantity of
insecticide is drawn into the pipette. The air drawn into the
needle forms a bubble about 3 mm. long (D in fig. 1) in the pi-
pette between the water and the insecticide (E). The level of the
insecticide is then read on the pipette. The scale on the board
is used only for approximate readings. The microinjector crank
is then turned in a clockwise direction until the desired quantity
of insecticide has been delivered on the tip of the needle. The
insect is then brought into contact with the drop of insecticide.
If the insecticide has the right properties, it will immediately
spread over the integument of the insect. Volumes of liquid of
one-half of one-thousandth of a ml. or larger can be measured and
applied to the insects with a pipette of this size.
To rinse the apparatus with distilled water, open the stop-
cock (B in fig. 1) and allow the water to flow through the pipette
.intil it is thoroughly rinsed.
The apparatus does not need any parts especially made for
it. and consequently it could be modified to fit the needs of the
user. A pipette of smaller bore would allow accurate readings of
smaller quantities. A glass tip on the pipette could be sub-
stituted for the metal one, to allow the uise of cleaning fluid
for removing insecticidal residues which cannot be removed by
Active insects may be held in the hand as shown in figure 2,
placed in small cages, chilled to immobilize them, or anesthetized
while the insecticide is being applied. Many slow-moving insects,
such as some lepidopterous larvae, may be treated during normal
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
-2 DIAGRAM OF MEASURED DROP APPARATUS
A-Distilled water reservoir
B-Stopcock f o r rinsing micropipette
C- Graduated micropipette
D-Air column between water and insecticide
F- Hypodermic needle
Figure 1.--Diagram of apparatus for ap.'lying measured drops of liqula
insecticides to insects.
g. ~ .. 1
Figure 2.--Photograph showing operation of apparatus for applying
measured drops of insecticide to the integument of insects.
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UNIVERSITY OF FLORIDA
* II IIItI ill II HH3 1262 08537 1028111
.1 3 1262 08537 1028
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