BUREAU OF ENTOMOLOGY. 405 



the mechanical viewpoint are met, which necessitate either producing 

 new types of machinery or modifying existing types. Probably the 

 most important development of the year along this line has been the 

 further improvement of the saddle dust-gun to the point where it is 

 now a commercial success. Particular attention is also being devoted 

 to the problem of developing dusting machinery which will permit 

 daytime operation. 



Chemical studies in cooperation with the Bureau of Chemistry and 

 the Insecticide and Fungicide Board have been enlarged and include 

 not only the improvement of calcium arsenate but also the possibility 

 of finding an even superior chemical for this purpose. One of the 

 most important discoveries of the year was the fact that there is 

 a very distinct chemical relation between the composition of the dew 

 on the cotton plant and the action of certain insecticides. It was 

 found that the dew on cotton plants is strongly alkaline, and this dis- 

 covery opens up many important possibilities while explaining some 

 apparent inconsistencies in the results of certain chemicals previously 

 studied. 



Other correlated problems which have received attention include 

 the electrical charging of poison dust and the classification of in- 

 secticides on the basis of physical characteristics. 



The invasion of the extreme southeastern States by tlie weevil 

 brought the species into contact with new conditions which will neces- 

 sitate some modifications in the problem of control. Therefore in- 

 vestigations in cooperation with the State of South Carolina were 

 inaugurated in a comparatively small way at Eastover and Sumter, 

 S. C, but in the spring of 1923 a more elaborate station was opened 

 at Florence, S. C, at which place an investigation of the entire weevil 

 situation in the southeastern territory was begun. Careful experi- 

 ments to test the different methods of weevil control advocated by 

 agencies outside of this department as well as the dry calcium arsenate 

 method were started. 



The relationship between cotton dusting and aphis injury to the 

 cotton plants was further studied. It was at first thought that the 

 reason for the abundance of aphids was the poisoning of the pred- 

 atory enemies of this species. Experiments to test this idea have 

 not been conclusive. It has been shown, however, that the cotton aphis 

 can be controlled by the use of nicotine dust with a hydrated lime 

 base used at the rate of 8 or 10 pounds per acre when the dust con- 

 tains 2 to 3 per cent nicotine. Practically complete control can 

 be secured from a single aj)plication. 



In the fall of 1922 experiments in the use of airplanes for the pur- 

 pose of applying insecticide dusts were inaugurated. The airplane 

 applications at that time were for control of the cotton leafworm^ 

 but many points were determined which apply to the problem of 

 weevil control. 



In the spring of 1923 experiments were started in direct control 

 of the boll weevil by means of airplanes. The results so far have 

 shown quite definitely that airplanes can be used economically to 

 control gross feeding insects such as the leafworm, but it has not 

 been determined as yet that they can be used for boll- weevil control. 



Studies on hibernation, together with correlated records on spring 

 emergence and distribution, have been continued and in the spring 

 of 1923 reached the point where it was possible to bring the records 



