STATE i^a-^.N^ BOARD 
 
 May 1949 ET-266 
 
 United States Department of Agriculture 
 
 Agricultural Research Administration 
 
 Bureau of Entomology and Plant Quarantine 
 
 A METHOD FOR TESTING RESIDUAL DEPOSITS 
 
 P. G. Piquett, R. H. Nelson, and E, R. McGovran \J 
 Division of Control Investigations 
 
 With the discovery of the new insecticides that leave long- 
 lasting deposits, it became necessary to find methods for testing 
 the effectiveness of the residues. The laboratory method presented 
 herein for testing the effectiveness of the residue of DDT caji be 
 used for other simi lar materials. 
 
 Apparatus 
 
 Twenty-six-gage galvanized iron was used to construct the frame 
 shown in figure 1, A. The two sides of this frame fitted the fronts 
 of two 9-inch cubical, screened fly cages with sliding glass doors 
 (figs. 2 and 3)» A slot l/U inch high and \\ inches wide was cut in 
 the middle of the lower edge of each of the metal strips which fitted 
 across the bottom of the glass doors. These slots were connected by 
 two 6-inch, L-shaped metal strips, one on each side of the slots 
 (fig. 1). These connecting strips were 1§ inches high, with an 
 additional l/l; inch turned inward on the bottom. 
 
 Two 6- inch lengths of l/U-inch bar steel (fig. 1, (1) and two 
 pieces of double- strength window glass ij by 6 inches (fig. 1, 1) 
 were cut. One piece of glass was placed between the L-shaped metal 
 strips connecting the slot openings, and a steel bar was placed on 
 each side of the glass. The other piece of glass was laid on top 
 of the bars. When the glass fronts of the cages were lifted above 
 the slot openings, a tunnel connecting the two cages was fonned 
 (fig. 3)» Flies from one cage could then walk over to the other, 
 the dimensions of the tunnel prohibiting flying across. 
 
 Testing Procedure 
 
 One side of each glass piece was treated with an acetone-refined 
 kerosene solution containing ^ grams of DDT per 100 ml. Only enough 
 acetone to dissolve the DDT was used. This solution was applied from 
 a pipette. One inch at each end of each piece of glass was not 
 treated. The remaining 6 square inches received 0.05 ml. of solution, 
 or 2.5 mg. of DDT. This deposit is equivalent to 6o mg. of DDT per 
 square foot. The application was allowed to dry overnight before use. 
 
 y 
 
 Now with the Office of Exper Jbnent Stations . 
 
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 One empty cage and one well stocked with 2- to 3-day-old flies 
 were joined by the apparatus. The tunnel was assembled as previously 
 described, the treated surface of the bottom glass facing up and 
 that of the top piece facing down. The glass fronts of the cages 
 were then lifted long enough to allow approximately 100 flies to 
 cross over. A fly required about 2 seconds to walk across. 
 
 Numerous tests were made vdth the apparatus. In one series of 
 six tests, when the DDT dosage specified above was used, an average 
 of 100.7 t 8.6 flies per test crossed the treated glass. The average 
 number of males per test was 48.8 ± ^.8 and of females 51.8 ± 8.0. 
 This is quite close to a 50-50 sex ratio. The mean mortality for 
 these six tests was 4-6.1 ±6.3 percent. The mean mortality for males 
 was A3.0 ± 7.5 percent and for females 45.7 1: 7.3 percent. 
 
 Relative toxicities of residues of various formulations can be 
 determined by this method. Studies of the effect of storage on 
 various insecticides can also be made by comparison with freshly 
 made standards. 
 
 Figure 1, — A, Metal frame for connecting two cubical fly cages. 
 B, Glass slides used in making the tunnel. C, Metal bars used 
 to hold the glass slides apart and form the tunnel. 
 
3 - 
 
 Figure 2. — ^Metal frame with the two cages attached. Looking down 
 on the tunnel. 
 
 Figure 3. — Metal frame with the two cages attached, showing com- 
 plete assembly. 
 
UNIVERSITY OF FLORIDA 
 
 3 1262 09240 9431