183 



to kill flies in the field was not demonstrated although its efficacy 

 was adequately proven in the laboratory tests. 

 Contact Residuals 



Adult house fly dosage-mortality curve for permethrin. Concentra- 

 tions of permethrin (JFU 5819 25% permethrin EC, ICI Americas, Inc.) 

 tested and responses are shown in Table k3. The probabilities, probits, 

 log doses, and upper and lower fiducial limits are shown in Table 50. 

 The dosage-mortality curve with fiducial limits is shown in Figure 39- 

 The LD50 for JFU 58 1 9 is 18.0 ppm and the regression equation is 

 Y - 14.25 + 1 -A6X. 



The high LD 50 and the relatively shallow slope indicate that some 

 amount of resistance to permethrin may already exist in this house fly 

 strain and that more resistance is developing within the gene pool. 

 Possible cross-resistance to chlorinated hydrocarbon insecticides may 

 explain this phenomenon as indicated in the literature (Prasittisuk 

 and Busv ine, 1 577) . 



The responses (Table ^9) are not well distributed between the 

 mortal i tv values of 10 and 90%. This is due to the fluctuation in 

 mortality rates produced by the same test concentrations on different 

 generations of the house fly colony. After 10 to 15 trials, the set 

 of data in Table ^9 was the most reliable set produced. 



Permethrin as a contact residual in the laboratory. Permethrin 

 (JFU 5021A 2 lb/gal EC, ICI Americas, Inc.) was applied to cement, tin, 

 and plywood templates to run-off at rates of 0.05 and 0.005%. 



Female "laboratory colony house flies, 3 to 5 days old, were trans- 

 ferred by use of a vacuum system to cylindrical window-screen cages 

 12.5 cm high and 7.0 cm in diameter. Open ends of the cages were placed 



