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 Maeda^ 
 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 90° 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 
 
 _l/ 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 siop (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 
 spindle. 
 
 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 m-icrometer 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 0.97 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- 
 meter 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 make it desirable to calibrate each one for accurate work and to 
 adjust the upper stop (jE) so as to deliver comparable volumes from the 
 different syringes. 
 
 Literature Cited 
 
 (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. Bui. 
 38: 93-101. 
 
 (2) Trevan, J. W. 
 
 1922. An apparatus for measuring small quantities of fluids. 
 Lancet (London) 202: 786, 
 
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