70 DDT — ^Killer of Killers 



sprays were prepared by making a kerosene solution of pyre- 

 thrum or an organic thioq^anate. Pyrethrum is a naturally- 

 occurring poison found in the blossoms of a daisy-like plant 

 grown in British East Africa, Belgian Congo, Japan, and 

 Brazil. The thiocyanates are synthetic chemicals sold under 

 the trade names of Lethane and Thanite. Pyrethrum is rath- 

 er unstable: when exposed to light or to the air it soon de- 

 composes. Thus, it has no lasting action. Pyrethrum, how- 

 ever, is a good killer, and because it is praaically odorless, \t 

 is much in demand for fly sprays. 



The thiocyanates are also effective killers, but they must 

 be used in much higher concentrations than pyrethrum. Dur- 

 ing the war when pyrethrum became scarce, practically all 

 household insect sprays were made with these synthetics. The 

 thiocyanates are more stable to light and oxidation than is py- 

 rethrum, but even they have no residual aaion. In other 

 words, a wall sprayed with a thiocyanate solution would not 

 continue to kill insects. One disadvantage of the thiocya- 

 nates is that they have an unpleasant and persistent odor 

 which lingers on for a long time in an area where the spray 

 has been used. 



Both pyrethrum and the thiocyanates, in addition to be- 

 ing good killers, have rapid knockdown properties. This is 

 important. When you use a space spray you want to get 

 rid of the insects in a hurry. It is no consolation to know 

 that they will be dead in a few hours. You want to keep 

 them out of your soup now. That's where rapid knockdown 

 comes in. The insects drop to the floor within a few min- 

 utes, although they may continue to live for another hour 

 or so. 



