THE GEAPE PHYLLOXERA IN CALIFORNIA. 99 



During the winter of 1913-14, two experiments were made on 

 the resistance of hibernants to hot water. The temperatures used 

 ranged from 116° to 137° F., and the duration of submergence 

 ranged from one to four minutes. A temperature of 120° F. failed 

 to destroy the aphids completely, while 125° F. with a submergence 

 of one minute destroyed all the insects. Similar treatment of the 

 roots of living vines resulted in no appreciable injury to dormant 

 plants. 



The same winter, between December 3 and March 17, a series of 

 nine experiments were carried out bearing upon the resistance of 

 hibernant larvae to submersion in water of ordinary temperatures. 

 Pieces of heavily infested grape roots were placed in petri dishes 

 under about 1 inch of water. The periods of submersion ranged from 

 48 hours (two days) to 1,512 hours (nine weeks). It was found that 

 with the lengthening of the submersion period the percentage of 

 aphicls succumbing increased. A submersion of six weeks, however, 

 resulted in the destruction of only 72 per cent of the aphids, one of 

 five weeks in 64 per cent mortality, the final test (that of nine weeks) 

 alone destroying all the aphids. In tests of from 48 to 168 hours' 

 submergence the temperature of the water averaged 47° F., in the 

 final test of nine weeks it averaged 55° F., and in four intermediate 

 tests of from three to six weeks, 53° F. 



In the light of the results of this series of tests the fact that a 

 practical vineyard submersion requires at least two months' flooding 

 is not a cause for wonder. 



An observation made during the winter of 1913-14, from Decem- 

 ber to February, showed that hibernant larvae can withstand short 

 intermittent submersions in water interrupted by periods of low 

 temperatures, even passing below 32° F. 



On June 9, 1914, two experiments were conducted, bearing on 

 the resistance of eggs of the radicicole to heated water. In four of 

 these tests the length of submersion was 90 seconds, and the tem- 

 peratures ranged from 112.1° to 131° F. ; in the other seven, the eggs 

 were submerged 60 seconds under temperatures varying from 108.5° 

 to 132° F. Eesults showed that a temperature of 123° F., with an 

 exposure of 60 seconds, destroyed all eggs. For practical use it is 

 desirable to have a temperature of at least 125° F. 



In the experiments the eggs after treatment were placed on pieces 

 of vine roots and observed for possible development. Temperatures 

 of 123° F. or over killed the eggs immediately, but the lesser tem- 

 peratures killed none or only a variable percentage. Those eggs 

 not killed hatched normally. 



During June and July-, 1914, a series of tests was made with 

 radicicole eggs exposed to atmospheric temperatures varying from 

 76° to 90° F. for periods varying from 5 to 60 minutes. With a 



