Xew Youk Agkicultukal Expekiment Statio^\ 371 



darker as the season advances, becoming salmon colored before 

 leaving the vines and changing to dark red in their winter hiding 

 places. There are many variations in color and color patterns 

 among individuals of the same species so that nine distinct species 

 have been described; but our leading authorities regard these 

 diverse forms merely as varieties of T. comes. 



CHAEACTER OF INJURY AND ECONOMIC IMPORTANCE. 



The grape leaf-hopper, being a sucking insect, secures its food 

 by inserting its proboscis or beak through the epidermis or skin 

 of the leaf, piercing the underlying tissue and sucking up the cell 

 sap. Having satisfied its hunger it withdraws its beak and wanders 

 about the leaf. With the withdrawal of the proboscis the injured 

 leaf tissue is exposed to the drying action of the air which not only 

 completes the destruction of the injured cells but dries out the 

 surrounding cells, thus causing a small portion of the leaf to die. 

 This area is small but the accumulative eifect is of importance in 

 the economy of the plant. These injured parts turn yellow and, 

 as the injuries increase by the feeding of the insects, the leaves 

 become dotted with spots until by September these areas are so 

 numerous as to cause the leaves to have a decidedly yellow appear- 

 ance when contrasted with healthy foliage. 



It is not unusual to find 100 leaf-hopper n^aiijihs on a single 

 leaf. If each insect should feed only twice each day and remain 

 on the leaf for a period of two months we would find that there 

 had accumulated on the leaf 12,000 injured areas. This would 

 be a moderate damage ; for counts show that leaves of average size, 

 if badly infested, may have as many as 20,000 such injured areas. 



Thus there are two factors in the work of the leaf-hopper: the 

 removal of the cell sap by the leaf-hoppers as food ; and the destruc- 

 tion of tissue by the drying out and death of the cells surrounding 

 those pierced by the insects. The latter is the more important 

 factor. The death of these cells means a lessening of the growth 

 of wood and a decrease in the yield of fruit. This is evident on 



