October, '21] morrill: nicotine dusts 395 



results which I have to offer at this time are for the most part fragmentary. 

 However, it is hoped that the miscellaneous observations here recorded 

 may prove of some value to others. 



Observations on the Use of Nicotine Dusts Against the 

 Grape Leaf-Hoppers 



It was found by various investigators in the season of 1920 that the 

 grape leaf-hoppers were susceptible to the effects of nicotine dusts but 

 to what extent these insects were actually killed seems not to have been 

 definitely determined. Reports in regard to the effectiveness of nicotine 

 dusts against the leaf-hoppers became rather conflicting early in the 

 present season and field tests were consequently undertaken in the Im- 

 perial Valley and later in the San Joaquin valley to discover the facts in 

 regard to this question. 



As a basis for work against the grape leaf-hoppers it was considered 

 necessary to make a study of the methods of checking results of nicotine 

 dust applications in vineyards. The method in common use consisted in 

 spreading papers or canvas under the vines to be dusted and observing 

 the hoppers which dropped on these comparatively smooth surfaces. 

 Other observers modified this method by dumping the dead and stupe- 

 fied insects from papers or canvas into pasteboard boxes or glass jars to- 

 gether with the dust which had dropped from the vine with the insects. 

 By these methods an element of uncertainty was introduced by the as- 

 sumption that the dusts which had dropped from the treated vines 

 had lost all toxicity. 



Among the methods tested by the writer were: (1) observing hoppers 

 which dropped onto papers and canvas spread under the vines (2) ob- 

 serving hoppers which dropped into an old galvanized bucket with rough 

 bottom (3) observing hoppers picked up with forceps from papers and 

 canvas within five minutes after applying dust to the vines and kept in 

 glass jars or vials (4) observing hoppers which dropped into a galvanized 

 bucket within five minutes from the application of dust to the vine and 

 which were dumped into a wire sifter to separate from dust and then into 

 a glass jar for observation (5) observing hoppers which dropped onto a 

 fine wire screen (about 50 mesh) through which most of the dust im- 

 mediately passed and (6) observing hoppers which were left lying as they 

 fell on the ground under the vines. 



The last mentioned method was the most tedious but was necessarily 

 the standard. The use of a fine wire screen (the inverted top of an in- 

 sect breeding cage was used in this observation) appeared to give results 

 which approximated those obtained by the standard method and the 



