200 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



on the part of the hoppers for particular varieties of grapes. In 

 the Lodi section the two chief varieties of grapes grown are the Tokay 

 and the Zinfandel. Throughout all this section, so far as we observed, 

 a distinct preference was shown for the Tokay over the Zinfandel. 

 The Mission vines are also readily attacked by the hoppers in this 

 section. In a particular vineyard, which contained these three varieties, 

 the Mission and Tokay were worst infested, the Mission a little worse 

 than the Tokay, while the Zinfandel was distinctly the least infested. 

 In a vineyard at Madera, which was under observation for some time, 

 the vines which were most resistant or were less readily attacked by the 

 hoppers were the Fehr-Yagos, Zinfandel, Alicante Bouchet, Petit 

 Bouchet, and Mataro. Of these the Fehr-Yagos and Zinfandel showed 

 the least injury. In this question of preference for varieties, of course 

 the difference in the degree of susceptibility of the varieties to an 

 equal attack of hoppers must be taken into consideration; /. ?., some 

 varieties may be more weakened than others, although the hoppers may 

 be present in equal numbers. The actual difference in the numbers 

 of hoppers, however, may be very readily determined by jarring the 

 vines and observing the numbers flying about them. The difference in 

 numbers in most cases is so great that there is little difficulty in judg- 

 ing this. The larger numbers of hoppers will always be found on 

 the vines showing the most injury unless, of course, it is on those vines 

 that are so badly injured that most of the food supply is gone and they 

 are obliged to go elsewhere for food. 



DEVELOPMENT. 



Length of Life Cycles. Hoppers hatching from eggs in midsummer 

 or early fall remain over winter and attack the vine as soon as the 

 foliage appears in the spring. Here they feed for a month, after 

 which egg laying begins, and which may continue for two months 

 longer. This will take it to midsummer again, so that the length of 

 this life cycle is approximately one year. Large numbers of overwinter- 

 ing hoppers were enclosed in cheese-cloth bags in the vineyard, and 

 the hoppers were observed to begin dying off in June, and by the last 

 of July practically all were dead. Hoppers hatching from eggs laid 

 in May and June begin laying eggs upon reaching maturity five weeks 

 later. Egg laying continues for a month or two longer, when they in 

 turn begin to die off, thus making the length of this life cycle from 

 three to four months. 



Number of Generations. The number of generations of the insect 

 as indicated above is two. Although these broods may overlap one 

 another they are very distinct, and, at least in the Lodi section in 1907 



