THE GRAPE PHYLLOXERA IN CALIFORNIA. 79 



vines (mostly resistants and American nonresistants) during Sep- 

 tember and October, and some were reared in the cellar during 

 August. 



In 1913 the first nymph was observed, July 9, on the root of an 

 American vine, and at about the same time others appeared on 

 young resistant hybrids in pots. On the severed pieces of vinifera 

 roots kept in jars in the cellar nymphs occurred as early as July 12, 

 and on July 17 the first migrants appeared. This was the first year 

 in which experiments were conducted with living vines in cages, 

 and on these the earliest nymphs and migrants were reared on 

 July 20 and 28, respectively. In the experimental vineyard (Zin- 

 fandel) migrants were first collected about August 1, but some 

 nymphs were found on July 25 in a vineyard at Napa, Calif. In 

 general, migrants continued to develop until November, but after 

 the middle of October their production was scanty, and in the vine- 

 yard very few were found later than September. 



In 1914 nymphs were first observed on June 16, both in the ex- 

 perimental vineyard at Walnut Creek and on roots kept in the 

 cellar. On June 18 a migrant was reared from a nj^mph collected 

 in the vineyard two days previously. On the roots of the vines 

 growing in cages nymphs were reared June 23. Throughout July 

 and August nymphs and migrants were abundant in the Zinfandel 

 vineyard. In September the numbers fell off rapidly and none were 

 found in October. In infested vines in pots migrants were secured 

 in considerable numbers throughout August and September, but 

 were much more scarce in October. 



In 1915, in the material reared under cellar conditions, the first 

 nymph was observed on June 14. The day following, a nymph oc- 

 curred on the root of a young vine planted in a section cage. In the 

 cages containing living vines, the first nymph was reared June 23, 

 and in the experimental Zinfandel vineyard, nymphs were collected 

 June 22 and evidently occurred as early as June 15. In the vineyard 

 the production of migrants continued until the end of September, 

 and was abundant from July 15 to the end of August. In the ma- 

 terial in the cellar jars, abundant migrants were secured throughout 

 the months of July, August, and September, and the production con- 

 tinued until November 8. 



In summing up, it may be said that in California the period in 

 which migrants are developed in vineyards extends from the middle 

 of June until the end of October ; that these forms appear in great- 

 est abundance from the middle of July to the middle of September 

 (the hottest time of the year) ; and that the production is very 

 limited in June and October. In small vines in pots, especially if 

 consistent irrigation is practiced, the October production of migrants 



