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 rooflike 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 hkely 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 2% 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 
aS» 
