8 BULLETIN 805^ U. S. DEPARTMENT OF AGRICULTURE. 



material. The plants were encaged before the hibernating adults 

 made their appearance in the nursery, thereby preventing outside 

 infestation. 



Special cages were constructed for experiments in determining 

 the length of the nymphal stages. Various types of cages were 

 tried in an effort to secure one in which the nymph could be reared 

 under as nearly normal conditions as possible. 



The type of cage finally decided upon was made as follows: A 

 piece of thin sheet-cork was cut about 2 inches square, in the cen- 

 ter of which a 1-inch square hole was made. White muslin cloth 

 was stretched tightly over one side of the cork and glued fast so as 

 to cover the center hole. Heavy wadding cut to the shape of the 

 cork, but leaving the center open, was glued to the other side. With 

 the muslin side out, the cage was then placed over a newly hatched 

 nymph on the lower surface of a leaf. A square of stiff cardboard of 

 the same size as the cork was placed on the upper side of the leaf, 

 and the cardboard, leaf, and cage were fastened together by paper 

 clips. The young nymph within the cage received ventilation from 

 both sides, through the porous wadding and through the muslin top. 

 The leaf tissue was protected against injury by the cardboard on its 

 upper surface and by the wadding on its lower surface. The nymph 

 was examined daily by removing the paper clips and lifting the cage 

 slightly; in this manner a record of the molts was obtained. 



Although this cage was a' little heavy when used on the small 

 leaves of seedlings, it proved satisfactory when fastened to the 

 larger leaves of two-year trees. For this reason the nymphal stages 

 were obtained by transferring newly hatched nymphs from globe 

 cages to the cork cages on uninfested leaves of older trees in the 

 nursery row. 



Number of Generations. 



There are three generations of the apple leafhopper at West Chester, 

 Pa. These generations overlap slightly but they are easily distin- 

 guished by the resultant injury caused by each. The first generation, 

 covering the period from the time of egg deposition by the overwin- 

 tered females to the death of the first-brood adults, extends from the 

 last week in May to the first week in August. The second generation 

 covers the period from the first week in July until the latter part of 

 September. The third generation, including the hibernating adults, 

 lasts from the first week in September until the early part of July of 

 the following season. Adults of this generation hatch during the first 

 week in September and remain on the trees until late in November 

 when they seek shelter for the winter. In the spring of the following 

 year overwintered adults are found on the trees from the last week in 

 May until death, which occurs during June and early July. 



