February, '22] headlee: contact dusts 75 



is concerned purity is a secondary consideration. The most satis- 

 factory material that we ever used runs only ninety-four per cent 

 arsenious oxide. 



Conclusion 



In addition to the above, there are doubtless many other uses to 

 which these low priced arsenicals can be put. The study of lower 

 priced remedies is an important branch of Entomology, for the finding 

 of a means of controlling an insect or a disease is of little value if the 

 material available as a remedy costs more than the damage. The 

 cost of treatment in proportion to the value of controlling pests varies. 

 Some apple spraying and dusting costs from twenty to thirty per cent 

 of the gross valtice of the control while occasionally potato spraying 

 will cost as low as five or even three per cent of the gross value of the 

 control. 



We know of hundreds of insects and diseases that could easily be 

 controlled, but which generally are left undisturbed on account of the 

 cost of control approaching or even exceeding the value of the damage 

 done and every reduction in cost of materials or methods of treatment 

 moves some of these pests from the class that cannot be profitably 

 combatted into the class that can be profitably controlled. 



President George A. Dean: Mr. T. J. Headlee will now present 

 a paper, 



SOME FURTHER EXPERIENCE WITH CONTACT DUSTS^ 



By Thomas J. Headlee, Ph.D. and W. Rudolfs, Ph.D.^ 

 Introduction 



The writers are not attempting in this paper to set forth a finished 

 piece of work but, in view of the large interest now existing in contact 

 dusts, have thought it well to give an account of some data obtained 

 both from the field and the laboratory in the hope that such action 

 might help to hasten the day when the actual worth of contact dusts is 

 known. The' senior author was led to undertake these studies because 

 of the tremendous demand on the part of potato growers for a dust 

 method of controlling the pink and green aphis (Macrosiphum solani- 

 folii) of potato and tomato. 



^Paper No. 73 of the Journal Series, N. J. Agricultural Experiment Stations, De- 

 partment of Entomology. 



^The chemical determinations have been made by Dr. Rudolfs, who since Sept. 

 16, 1921 has been filling the position of Bio-Chemist in Entomology at the N. J. 

 State Agricultural Experiment Station. 



