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A. pomi is the most abundant and widespread species, causing much 

 injury every year in bearing orchards and in nurseries, and remaining 

 upon apple throughout the season, without migration to other hosts. 

 The characteristics distinguishing the three species are detailed. To 

 avoid confusion in the identity of A. pomi, the synonymy is discussed 

 at length and a useful bibliography is given. The view is expressed 

 that this species had been imported into America prior to 1854. 



A summary of the life-history of A. pomi has been given previously 

 [R.A.E., A, iv, 484]. Brittain has reported that in Nova Scotia on 

 different varieties of apple the eggs hatch at the time when the buds 

 on such varieties are showing green. Whether this will prove correct 

 for other parts of the country remains to be seen. It is known that 

 a very large percentage of the eggs do not hatch, so that predictions as 

 to outbreaks cannot be made from any examination during the dormant 

 season. Factors that are generally considered to hinder the eggs from 

 hatching are climatic conditions, such as sudden drops in temperature 

 or periods of cold rain, predaceous birds and insects, and non-fertilisa- 

 tion of the eggs. It is doubtful whether non-fertilised eggs of this 

 species will survive the winter and hatch in the following sprrug. The 

 activities and reproductive capacity of the various generations is 

 discussed and recorded in a series of tables, reproduction in the stem- 

 mother being found to extend from the beginning of the blossoming 

 period almost up to the beghining of the normal June fruit-dropping 

 period. The various nymphal stages are described. From early June 

 onwards there are 14 viviparous generations following in rapid suc- 

 cession and requiring from 8 to 12 days to reach maturity, the maximum 

 period being for the 8th generation at the end of July and the 10th 

 generation in the latter half of August. The third and later generations 

 are the most injurious, congregating not only on the leaves and causing 

 them to curl, but also on the rapidly growing shoots, the fruit stems 

 and the fruit. The young shoots become stunted or die, and the young 

 fruit is dwarfed and gnarled, though the rosy aphis {A. sorbi) is the 

 more seriously injurious in these respects. 



The maximum productive period (31 "6 days) is for the stem-mothers, 

 the next being 30-2 days for the 13th generation. The minimum 

 productive period (13*7 days) is for winged females of the second 

 generation. The productive period varied considerably for the other 

 generations, though it was in general shorter during the warmer part of 

 the summer. The average daily production increased from 1 '85 in the 

 case of stem- mothers to 4-13 for the 5th generation and then gradually 

 declined to 1-77 for the 13th generation. In the rearing cages the 

 14th generation produced the sexual forms, the males however con- 

 stituting scarcely 1 per cent, of the sexual generation. In the case of 

 A. po?ni, the production of winged forms is for the purpose of distri- 

 bution only and not for migration to different food-plants. In the 

 rearing-cage work practically every generation produced a few 

 winged forms, though the earlier generations give rise to the highest 

 proportion in order to ensure widespread distribution. Although 

 the factor of crowding was eliminated in the author's rearing work, 

 the percentage of winged forms for any one generation did not seem 

 to vary. This question of the production of winged forms requires 

 further study and the results may prove of great economic importance. 



(G33) B 



