36 EXPERIMENT STATION BULLETIN 354 



concentrate were determined, as well as advantageous inerts for com- 

 pounding dust concentrates. The results of these investigations were in- 

 corporated in selected formulae which then became the basis for distribu- 

 tion of supplies of the new conipound to other experiment stations 

 throughout the country. Since only limited amounts of the new compound 

 are available (because supplies of it in large quantity are needed for the 

 Armed Forces) the procedure followed avoided unnecessary duplication 

 of effort. 



Applications of a contact insecticide by means of an "aerosol" were 

 studied extensively. In an aerosol the insecticide, in the form of a non- 

 volatile liquid, is dissolved in a liquefied gas which is confined under pres- 

 sure in a small metal cylinder. Release of the contents through an appro- 

 priate orifice results in vaporization of the liquefied gas containing the 

 toxicant, and thus breaks up the non-volatile insecticide into extremely 

 small particles which float in the air. Distribution of the toxic particles 

 is rapid and complete, and performance of the toxicant is highly effective. 



A special room for study of aerosols was arranged. Walls and ceiling 

 were given a coat of enamel which could be washed down with a solvent. 

 With the room darkened, a beam of light discloses distribution of floating 

 droplets through reflection of light from very minute particles which other- 

 wise would be invisible. It was found that insects could be confined in 

 cages in the room and would react normally to the floating particles when 

 a current of air was delivered through the cages. This technique was 

 thoroughly tested in many replicated experiments. 



Utilizing this plan, many formulae were studied. These included the 

 new chemical D D T, dissolved in an appropriate solvent. Experiments 

 proved that the non-volatile contents of an aerosol might be increased to 

 20 per cent or more, as compared with the 10 per cent hitherto considered 

 an upper limit. Thus, a given container would have twice the effective 

 capacity. 



Aerosol containers are being supplied in very large quantities to the 

 Armed Forces. Samples from the production lines of the principal manu- 

 facturer are submitted from time to time to this department for biologic 

 test, as a check-up on efBciency. 



Since dust applications on plants and on insects may be quickly re- 

 moved by rain, the addition of a tenacity agent to a dust is important. In 

 the same way insoluble materials suspended in water and applied as a 

 spray are likely to show greatly increased efficiency if the deposit on plants 

 or insects can withstand subsequent rain. Many proposed tenacity agents 

 have been tried by various experimenters. A new material which the de- 

 partment has helped to develop is giving results superior to those shown by 

 any other material hitherto proposed. 



The new compound is water-soluble but is sensitive to light. On ex- 

 posure to a moderate amount of daylight it becomes completely insoluble 

 in water. Addition of the new combination to a typical insecticide dust at 

 the rate of 4 per cent or less by weight renders the dust highly resistant to 

 subsequent rain, providing the application is made when the plants are wet 

 with dew. The same new compoimd has an important bearing on fungi- 

 cides which are not tenacious on foliage. Thus, such a material as basic 

 copper sulphate, which has little tenacity, adheres strongly to foliage when 



