﻿THE GRAPE LEAFHOPPER IN THE LAKE ERIE VALLEY. 31 



of which there are five. (See PI. I.) The average length of the 

 nymphal period is about 28 days, but with many it varies from 20 

 to 35 days. At the last nymphal molt the adults .have fully devel- 

 oped wings. A few newly transformed adults may be found in 

 vineyards from about July 7 to July 12. 



In normal seasons, however, the majority of the first-brood adults 

 appear after the middle of July. Observations of the development 

 of the insect indicate that if the nymphal period is lengthened by low 

 temperatures during the month of July, the number of adults of the 

 new brood that will mate and deposit eggs for a second brood is 

 quite small; whereas, if high temperatures prevail during the early 

 part of July, a large number of the nymphs are likely to develop 

 rapidly and make their transformation about the middle of July. 

 These early maturing adults mate and deposit eggs, and the resulting 

 second bipod of nymphs is quite large. 



Mating of the first-brood adults appears to be common for only a 

 few days. * In 1912 few mating pairs were seen except during the 

 period from July 23 to July 27. 



Early in August the color markings on the elytra of the adults 

 change from light yellow to a pale salmon color, which becomes 

 more intense as the season advances. After the appearance of this 

 change in coloration of the elytral markings little oviposition occurs. 



By the early part of September most of the nymphs of both the 

 first and second broods have transformed to adults, although a small 

 number of nymphs may be found on the foliage until quite late in 

 the fall. Toward the middle and latter part of September the adults 

 commence to migrate from the vineyards and during warm, calm 

 afternoons may be seen in swarms drifting through the air in an 

 apparently aimless manner. They usually come to rest in adjoining- 

 woodlands or rough pasture lands. Here they remain more or less 

 active during the warmer parts of the days of October and the late 

 fall, seeking the shelter of leaves and trash at night and during the 

 cooler days, and becoming less active as the cold weather of winter 

 approaches. 



REARING CAGES USED. 



Since the adult grape leafhoppers are very agile creatures it was 

 impossible to study their habits and life history in detail on the 

 large fruiting vines in the open vineyard. Yet in order that the 

 adults might oviposit and the eggs develop normally, it was neces- 

 sary that the insects studied should be confined on healthy growing- 

 grape foliage. For this purpose a large number of young grape- 

 vines, including several varieties, were planted in the garden of the 

 laboratory early in the spring of 1912. The vines were planted in 

 rows about 3 feet apart. Those vines used for securing egg records, 



