STATIB PLANT BOARD
April 1953 ET-306
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
A MICRODEVICE FOR RAPID APPLICATION OF TOXICANTS
TO INDIVIDUAL INSECTS
By C. C. Roan and Shizuko Maedai/
Division of Fruit Insect Investigations
In the topical application of reproducible amounts of toxicants to
individual insects accuracy is the most important requirement, but
ease and rapidity of the operation are also desirable. Trevan (2)
proposed the use of a micrometer to actuate a glass syringe for
measuring small volumes of liquids. Although this device is reason-
ably accurate, the operator is required to read the micrometer and at
the same time devote his attention to each individual test organism.
March and Metcalf (1) described a similar device with a spring attach-
ment which acts as a click micrometer. It requires less attention
from the operator in determining the volume delivered, but as the
micrometer thimble advances towards its inner limit the spring tends
to drag and incorrect amounts may be indicated.
The instrument described here makes use of a positive-action
ratchet which advances the micrometer spindle as a control lever is
moved through a predetermined arc; in this way the possibility of
errors due to improper micrometer readings is eliminated.
The dimensions of this device, shown in figure 1, may vary with
the type of micrometer selected. The micrometer frame is cut off
at a point J., so that the syringe holder (K) and the micrometer can be
mounted along the same longitudinal axis, with the ends of the syringe
plunger and the micrometer spindle in juxtaposition at I. The syringe
is fitted with either a hypodermic needle for injection or a similar
needle with the point ground off square and bent at a 900 angle for
topical applications. The ratchet wheel (C) may be turned from brass
or any other suitable metal. It is secured to the micrometer thimble
(D) by a friction fit. The ratchet grooves are machined so that the
j The authors acknowledge the work of the N. Shestopal Machine
Shop, Honolulu, T. H., in perfecting the ratchet-drive mechanism, and
that of workers in various laboratories who have contributed their ideas
in the design of such an instrument.
leading edges are equivalent to and opposite the divisions on the micro-
meter thimble. The ratchet wheel is machined with offset shoulders,
which act as bearings for the control lever (H). This lever carries the
ratchet pawl (G), which with its spring exerts enough pressure on the
micrometer thimble to insure its movement during the down stroke of
the control lever. The end of the pawl slides over the surface of the
ratchet wheel during the up stroke of the control lever when the ratchet
wheel is held stationary by the ratchet stop (B). This stop, which rides
on the ratchet wheel with the pressure of spring A, prevents the wheel
from rotating when the control lever is raised. The adjustable upper
stop (E) and the fixed lower stop (F) determine the arc through which
the control lever moves, and thus the amount of forward motion of the
The control lever moves forward with the micrometer thimble as the
device is operated, since it has as its bearings the offset shoulders of
the ratchet wheel. The rachet stop and spring also slide forward on
appropriate supports. To reset the micrometer the ratchet pawl is dis-
engaged by pulling the handle back into the slot in the control lever and
the ratchet stop is raised and slipped to its outer limit. The pawl and
stop are then replaced.
The accuracy of the modified micrometer mechanism depends on
that of the micrometer and also on the accuracy with which the ratchet
grooves are machined into the ratchet wheel. The major limiting factor
in the accuracy of delivery is the uniformity of the bore of the syringe.
A 0.25-ml. glass syringe was calibrated with the ratchet-driven
micrometer with triple-distilled mercury as a calibrating medium. The
results of these tests indicated that, within the same region of the
syringe, an advance of 0.005 inch of the micrometer spindle delivered
from (".97 to 0.99 microliter through a 27-gage hypodermic needle.
Since a volume of about 1 microliter was desired, the adjustable upper stop
was set so that the movement of the control lever advanced the micro-
neter spindle 0.005 inch. The volumes delivered from various regions
of the syringe ranged from 0.95 to 1.13 microliter. Variation in syringes
may 1nake it desirable to calibrate each one for accurate work and to
aidjist thc upper stop (E) so as to deliver comparable volumes from the
(1) March, R. B., and Metcalf, R. L.
1949. Laboratory and field studies of DDT-resistant house flies
in southern California. Calif. State Dept. Agr. Bul.
(2) Trevan, J. W.
1922. An apparatus for measuring small quantities of fluids.
Lancet (London) 202: 786.
UNIVERSITY OF FLORIDA
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