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BULLETIN 19, U. S. DEPARTMENT OE AGRICULTURE. 



The number of days required to complete the stages of the nymph 

 were arrived at as a result of rearing 114 nymphs through all of the 

 five nymphal stages from hatching to adult during the season of 1912, 

 and the data given above are based on these rearings. It was observed 

 that variations in temperature greatly influenced the length of the 

 different stages. It was also noted that although there might be a con- 

 siderable variation in the number of days that were required by nymphs 

 of the same age to complete any one of the stages, the total number of 

 days covered would vary but slightly ; since it frequently happened that 

 when one stage was protracted beyond the average period, some other 

 stage would be considerably shortened, and thus the total number of 



days for the entire nymphal period would 

 be about the same for all nymphs of the 

 i0\ same age. (See Table XL) 



SEASONAL HISTORY. 



ACTIVITIES OF ADULTS IN EARLY SPRING. 



The adult grape leafhoppers become 

 active in their hibernating places beneath 

 accumulations of leaves, trash, and dried 

 grass during the warm days of late winter 

 and early spring. During the warm sunny 

 hours of such days they rise in swarms 

 about one's feet when tramping through the 

 leaves and dried grass of woodlands and 

 swales which adjoin vineyards which were 

 heavily infested during the preceding sea- 

 son. During these periods of activity they 

 feed on the green parts of almost any plant that happens to be growing 

 near these places of hibernation. At first the green blades of tufts 

 of grass or the leaves of goldenrod or wild strawberry, and a little 

 later the unfolding leaves of wild raspberry and blackberry, appear 

 to form a favorite part of the menu offered by the woodland growth. 

 As the days beoome warmer the adults extend their flight and feed 

 upon the tender unfolding leaves of nearly all kinds of shrubs and 

 undergrowth. When the new growth of the cultivated grapevine has 

 attained a length of a few inches there is a general migration of the 

 insect to the vineyards. This migration occurs about the middle 

 of May in the vineyards of the Lake Erie Valley, and if the days are 

 warm and bright the desertion of the woodland food plants for the 

 foliage of the cultivated grapevine in the course of a few days is quite 

 complete. In the spring of 1912 this migration from woodlands com- 

 menced about May 20. On May 24 the leafhoppers were extremely 

 scarce in woodland places, where until four or five days previous they 

 had been present in swarms since the time of first activity in spring. 



Fig. 12. — Anal segments of male grape 

 leafhopper and details: a, Anal seg- 

 ments; 6, genital hooks; c, superior 

 clasper; d, inferior clasper. Greatly 

 enlarged. (Original.) 



