42 BULLETIN 19, U. S. DEPARTMENT OF AGRICULTURE. 
The most effective time to make the tobacco spray application 
against the nymphs is just before those that hatched earliest in the 
season have reached the fourth molt. This can be determined by 
the length of the wing pads (PI. I) which, in the fourth stage, extend 
about one-third the length of the abdomen. At this time a larger 
number of nymphs are likely to be present on the vines than at any 
other time during the season. In the vineyards of the Lake Erie 
Valley this condition occurs toward the end of the first week in July, 
and the most effective work with the tobacco-spray liquid may be 
done during the two weeks following this date. After this period, 
or toward the end of July, a large percentage of the nymphs of the 
first brood will have transformed to winged adults, and these latter 
can not be successfully treated with the diluted tobacco spray. 
In vineyards where black-rot, mildew, the grape rootworm, and 
the grape-berry moth occur, it is suggested that arsenate of lead 
and Bordeaux mixture be used with the tobacco extract to take the 
place of the second spray application in the schedule of treatment 
recommended against these diseases and insect pests. 
When it is deemed expedient to use sticky shields to capture the 
winged adults before oviposition takes place, the best sticky sub- 
stance for this purpose, according to Slingerland, is a mixture of 
melted resin, 1 quart, in 1 pint of castor oil, smeared liberally over the 
face of the shield. 
CONCLUSIONS. 
Typhlocyba comes, the species of grape leafhopper discussed in 
this paper, is at the present time a very destructive enemy of the 
grapevine throughout the vineyards of the Lake Erie Valley. For 
several seasons it has caused great losses to the vineyardists of this 
region by reducing the yield and quality of the grape crop and by 
curtailing the growth and lowering the vigor of the vines. The 
vineyardist who desires to maintain his vines in full vigor and produce 
high-quality fruit can not afford to allow this pest to develop in 
destructive numbers in his vineyards, for if not controlled sooner or 
later it is almost sure to occasion serious loss. Field experiments 
prove conclusively that this pest can be controlled by spraying 
against the nymphs with a tobacco-extract solution. 
The life-history studies recorded in the preceding pages show that 
there is only one full brood of nymphs a year in the region of the 
Great Lakes. 
The spraying experiments recorded in Part I of Bulletin 97 and 
Part I of Bulletin 116 of the Bureau of Entomology indicate that a 
single thorough spray application, made when the greater percentage 
of the nymphs of this brood is present on the underside of the grape 
leaves, will so reduce their numbers that injury to the crop and the 
