8 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 



means of controlling the grape leafhopper, and are turning their at- 

 tention toward a summer spray treatment as a means of control. 



The active movements of the overwintering adult "hoppers " when 

 feeding upon the new growth of vines in the early spring and the 

 fact that they are somewhat protected by the wings (which, when 

 the insect is at rest, form a roof like covering over the softer parts 

 of their body) (fig. 1) , greatly lessen the efficiency of a contact spray, 

 first, because of their rapid movements, and, second, because, even 

 if hit by the spray, they are not destroyed unless it is of so great 

 a strength that it would injure the tender new growth of the vine. 



Another device for the destruction of these overwintering adults 

 has been the use of shields smeared with some sticky substance. 

 This method, however, is quite laborious, and is practicable only for 

 small areas, and in the opinion of the writer is necessary only when 

 the overwintering insects are very numerous and likely to work 

 great injury to the new growth. 



In view of the difficulty to be encountered in overcoming the over- 

 wintering adults, and confident that this pest can be controlled by a 

 spray treatment applied during the nymphal stage, the experimental 

 work of the bureau was confined entirely to a spray treatment against 

 the nymphs. 



These experiments were undertaken in portions of vineyards which 

 had suffered from attacks of this pest for several years and in which 

 it was becoming more destructive each year, and although the over- 

 wintering adults were quite numerous and their injury to the new 

 shoots was much in evidence, no attempt was made to check them 

 in any way. 



SPRAY APPLICATIONS AGAINST THE NYMPHS. 



From the middle of June, when the nymphs first commenced to 

 appear, a close watch was kept on their development, the object being 

 to determine approximately the date at which the maximum number 

 of nymphs would be present upon the foliage before those earliest 

 to hatch had developed wings and before serious injury to the foliage 

 (evidenced by a yellow mottling of those leaves most heavily infested 

 by the nymphs) had become apparent. During the summer of 1910 

 this date was about July 12. At this time a small number of the 

 nymphs earliest to hatch had entered upon their last molt (fig. 3), 

 and the number present upon the leaves in earlier stages of develop- 

 ment was very large, indicating that about the maximum number 

 of nymphs was now present upon the foliage. 



The first spray application was made July 12, the substance used 

 being blackleaf tobacco extract, a dark, almost viscid liquid contain- 

 ing 2f per cent nicotine. 



Since no data were at hand to indicate the minimum strength at 

 which the solution would kill the nymphs it was necessary to spray 



