36 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 



Hibernants on nodosities sometimes keep these fresh until spring 

 by the stimulating action of their implanted beaks. Such nodosities, 

 especially in vinifera and labrusca vines, otherwise usually fail to 

 pass the winter in a fresh condition, as they are susceptible to rot 

 through moisture. 



DURATION OF IN STAR. 



With the exception of the winter egg, the hibernant instar is the 

 longest found in the life cycle of the phylloxera. A series of experi- 

 ments undertaken in the laboratory during the winter 1911-12 showed 

 that the average for 12 individuals was 183 days, or approximately 

 half a year. A later series of experiments, which took place both 

 on living vines and in the cellar on severed roots, indicated that 

 this period may be shortened to four and one-half months and length- 

 ened to seven and one-half months, dependent, as usual, on food, 

 temperature, and moisture conditions, and that six months is about 

 the average period for the development of the hibernants. This 

 period was considered from the date in the fall on which the insect 

 hatched from the egg to that on which the insect became mature the 

 spring following. The actual state of dormancy is from three to six 

 weeks shorter, and thus approximates five months. Granted that 

 radicicoles may live for three months after reaching maturity, it 

 is apparent that hibernating phylloxeras might attain a total longev- 

 ity of over 10 months. 



MOVEMENT ON THE ROOTS. 



On a sound root, the overwintered phylloxeras rarely change their 

 positions while they develop. If situated on tuberosities or nodosi- 

 ties, they cause these lesions to become enlarged, and if situated on 

 the normal root surface they cause the formation of new lesions. 

 Occasionally they develop without causing a lesion to appear. On 

 decayed and decaying roots, they move away after the first or later 

 molts and seek better food. This movement is both upward and 

 downward, indiscriminately, and is never extensive. The individ- 

 uals show only feeble inclination toward migration. This genera- 

 tion appears to be the lowest in vitality and the quickest to succumb 

 to adverse conditions. 



GROWTH AND MATURING OF THE HIBERNANTS. 



During the true hibernation period the phylloxeras apparently 

 take no food, and if any be taken no increase in growth can be noted. 

 Later a slow but appreciable growth may be observed, which indi- 

 cates the termination of the true hibernation period. A growing 



