180 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



labrum 



labium 



vents the berry from maturing properly since it is in the leaves of 

 the plant that the sugar of the berry is manufactured. The grape 

 thus loses much of its flavor and sweetness, and likewise the char- 

 acteristic coloring, which is so desirable in certain table varieties, is 

 not attained. The fruit, furthermore, is badly smutted by the exuda- 

 tions of the insects, and this serves as a harboring place for the 

 collection of dust and dirt, and for the growth of fungi (Fig. 3). 



The dropping of the leaves or any 

 interference with their normal func- 

 tions likewise has its effect on the 

 growth of the wood of the vine. The 

 canes fail to ripen normally for the 

 next year's wood, and many of the 

 buds fail to develop in the following 

 spring. The vine may thus be more 

 or less permanently stunted in growth, 

 and even killed in severe cases of 

 Mandibles grape leaf -hopper injury. 



Distribution; General. The grape 

 leaf -hopper (Typhlocyba comes Say) 

 is a widely distributed native Ameri- 

 can insect occurring in the United 

 States practically wherever the vine is 

 grown. It is frequently notably in- 

 jurious in the grape belts of New 

 York and Ohio, as well as other less 

 important grape sections in this 

 country. In Europe this species is 

 replaced by two other related species, 

 Typhlocyba flavescens and Typhlocyba 

 viticola. The former seems to be the 

 Much en- m0 re 'injurious of the two and occurs 

 throughout all of temperate Europe 



and northern Africa, while the latter is confined mostly to Italy 



and the neighboring islands. 1 



Local. In California our species is found in practically all of the 

 vine growing sections, but is most injurious in the Sacramento and 

 San Joaquin valleys. In the coast valleys another larger species 

 (Tettegonia atropunctata) is frequently injurious, most commonly 

 during the earlier part of the season. This species appears not to 

 feed exclusively on the vine, and during midsummer and later is 



\ Maxillae 



Fig. 4. The beak, or mouth-parts, of 

 the grape leaf-hopper, 

 larged. 



1 Mayet's Insectes de la Vigne, 168. 



