﻿34 BULLETIN 19, U. S. DEPARTMENT OE AGRICULTURE. 



NATURAL CHECKS. 



It would seem, however, that there are some as yet unknown 

 natural checks which greatly reduce the numbers of this insect and 

 occasionally almost entirely eliminate it over areas where only a short 

 time previously it had been a serious pest. 



In 1865 Trimble observed that once when the thermometer reached 

 100° F. thousands of the "hoppers" were killed. 



There was a great diminution in numbers of the adults in the 

 infested area of the Chautauqua County vineyards early in the season 

 of 1903. 



A' condition similar to this was observed by Mr. E. W. Scott, of 

 the Bureau of Entomology, during the season of 1912, when adults 

 of Typhlocyba tricincta were so very abundant in the vineyards near 

 Benton Harbor, Mich., that the vineyardists became greatly alarmed, 

 many of them making preparations to spray the nymphs when they 

 should appear. Yet this proved unnecessary, for when the time arrived 

 for the nymphs to appear upon the foliage in large numbers most 

 of the adults had disappeared and very few nymphs of the new 

 brood had hatched. As yet nobody appears to be able to account 

 for these sudden disappearances of the pest or to determine whether 

 they are due to climatic or other causes. 



In September, 1890, Thaxter observed that in Connecticut grape 

 leafhoppers in large numbers were injuring a vineyard. He found 

 that they were attacked by a fungous disease (Empusa sp.) which 

 apparently destroyed all of them. Tins is the only case on record 

 in which this insect was attacked by a fungous disease. Nothing of 

 this nature has been observed in the vineyards of the Lake Erie 

 Valley during the present investigation, and for the past four or five 

 seasons the pest has steadily increased. Probably the time may not 

 be far distant when large numbers of them will suddenly disappear, 

 as happened at Westfield, N. Y., in the season of 1903. However, it 

 is by no means safe for the vineyardist to count on these natural 

 checks, for while one is waiting for relief from such a source the pest 

 may work incalculable damage to his vineyard. 



REMEDIES. 



During the period that this insect has attracted the attention of 

 economic entomologists much experimental work has been undertaken 

 to determine the most effective means for its control. Early in the 

 control work undertaken against this pest, tobacco, in some form or 

 other, was employed as a killing agent. In 1828 Fessenden (see 

 Bibliography) recommended the smoking of infested vines by burning 

 tobacco stalks beneath them. 



