March, '08] ENTOMOLOGICAL NEWS. 123 



The grape Phylloxera (Phylloxera vastatrix} produces an 

 abundance of winged individuals in Europe and elsewhere in 

 the United States, but in California winged forms are extremely 

 rare. This possibly corresponds with the high ratio that soda 

 and potash bear to magnesium in our soils. 



Mr. O. Butler, of this department, has suggested to me that 

 since winged forms are produced on the finest roots near the 

 surface of the ground, their absence in this State might be bet- 

 ter explained by the almost invariable destruction of such roots 

 in this dry climate. 



The occasional production of broods of winged Phylloxera 

 may be due to variations in the annual rise and fall of alkali, 

 thus affecting the ratio of the different salts near the surface of 

 the ground, thus conforming to the chemical theory of wing 

 production, or the explanation may be that a better moisture 

 condition on such years may permit sub-surface rootlets to live 

 long enough to produce a brood of winged individuals. The 

 reason for the development of winged forms on these upper 

 rootlets may be according to the second explanation, the slow 

 drying out of these parts or their periodical wilting during the 

 summer resulting in a condition comparable with that occur- 

 ring now in our cabbage fields. 



Similar phenomena occur in this region in the case of num- 

 erous other species of plant lice. They increase until they 

 reach a point where the leaf will be brought, by their combined 

 attack, to a semi-wilted condition, and then all the young sub- 

 sequently produced will develop wings. Whole trees are thus 

 sometimes spontaneously freed from plant lice. 



It is well known that wing-producing lice develop much more 

 slowly than those that remain wingless. The present sugges- 

 tion is that a slower development, either immediately before or 

 after birth, is the exciting cause of wing formation.- 



The foregoing is presented with the hope that others will 

 make observations, the coming season, of evidence of spontan- 

 eous wing production and its relation to dry periods or to 

 excessive infestation of the plant. 



