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



three daily, at first exceeding that number. These eggs were typical 

 radicicole eggs, and produced further radicicole generations. Twelve 

 of the eggs laid August 21-24 were transferred to another root of 

 the same vine (Thompson's Seedless) and four insects matured 

 between September 28 and October 5, after an average egg stage of 

 about seven and one-half days and an average growing period of 35 

 days. The progeny of these four became hibernants, several of which 

 matured and oviposited the following spring. These experiments 

 demonstrate that under California conditions it is possible for larvae 

 hatching in galls to mature on the roots and become typical radici- 

 coles. No observations were noted regarding the characteristics of 

 the newly hatched gallicoles used in the experiments. After the 

 inoculation, July 16, of 50 eggs on the root of the living vine it was 

 seen that most of these eggs turned dark brown and failed to hatch. 

 The observations on the hatching of this batch of eggs indicate that 

 those failing to hatch were the earliest deposited, and it may be that 

 the change in conditions and environment affected the embryonic 

 development adversely. 



The present nonappearance in California of the gallicole and its 

 work on the foliage of grapevines, a condition paralleled in certain 

 portions of Europe, vitally affects the entire biology of the insect, 

 since it has been ascertained that the phylloxera issuing from the 

 winter egg can only exist on the leaf or petiole as a gallicole. The 

 Italian investigators Grassi, Topi, Grandori, and Foa found that no 

 larvae hatching from winter eggs fastened on the roots and that 

 all of this generation of stem mothers (fundatrices) had the galli- 

 cole characteristics. This is a very important biological point. It 

 is borne out by observations in those parts of Europe where the 

 gall form is absent and in which winter eggs are extremely rare. 

 It is similarly borne out in the phylloxera regions of California, 

 where similar conditions occur. During the winters of 1912-13 and 

 1913-14, an extensive series of vines, large and small, of all types, 

 many of which had been infested the previous summer with winged 

 phylloxerse, and others which, while themselves uninfested, had been 

 growing near such infested vines, were examined. With only one ex- 

 ception, no trace of winter eggs or dead sexuals was found. This ex- 

 ception consisted in the single winter egg noted under the preceding 

 heading. 



EFFECTS OF WATER AND HEAT ON PHYLLOXERA. 



Experiments were carried out to determine (1) the resistance of 

 hibernant larvae and eggs to water heated to various temperatures, 

 (2) the resistance of hibernant larvae to submersion in water at ordi- 

 nary temperatures, and (3) the resistance of eggs to the heat of the 

 sun. 



