462 EXPERIMENT STATION RECORD. [Vol.35 



cause the plants to wither, become dry, and finally die, usually before the crop 

 has matured. This aphid changes food plants usually four times during the 

 season, those serving as hosts in this region including crimson clover, garden 

 peas, red clover, sweet peas, Lespedeza sp., vetches, alfalfa, sweet clover, alsike, 

 white clovers, and shepherd's purse. 



" In general the pea aphid passes the winter on clovers, in April they migrate 

 to garden peas, upon which they feed until the first part of July. They then go 

 to the summer food plants, which include sweet clover, Lespedeza sp., alfalfa, 

 and the clovers. During August they return to garden peas, where they remain 

 until November and December, when they migrate for the fourth time, this time 

 returning to the clovers, upon which the winter is passed. The foregoing 

 statements of the migrations apply to the majority of the aphids, for doubtless 

 many individuals continue to breed on the clovers throughout the year. 



" No true oviparous females or the eggs of the species, have been found in 

 this region, although a few males were collected on garden peas in November, 

 1914. The viviparous females which pass the winter enter into hibernation 

 during December and commence reproducing in March. No reproduction, and 

 very little feeding, has been observed during January and February. 



" The presence of many parasitic and predacious enemies, together with the 

 aphidid fungus, tend to keep the aphids in check during the summer. 



" In 1914 there were 21 generations produced between May 1 and December 



10. In 1915 there were 22 generations between March 19 and December 5. The 

 age at which females began reproduction varied from 7 to 26 days, it being 

 noticeably longer in the spring and fall than during the summer. From a 

 series of 87 individuals the average age at which reproduction commenced was 

 12.1 days. The length of the reproductive period varied from 4 to 36 days, an 

 average for the two seasons of 84 records being 18.1 days. The period between 

 the birth of the last young and the death of the female, from 74 records, 

 averaged 1.2 days. The average length of life of viviparous females, from 83 

 records, including two seasons, was 31.7 days. The average length of life of 

 hibernating females was 134 days. 



" The number of young born per day by viviparous females varied from 1 to 



11. The total maximum number born by any one female was 142. The aver- 

 age number born per female, from 83 records, was 80.7 young. The fecundity 

 of the females was greatest during July, August, and the early part of Septem- 

 ber. It has been found that the wingless viviparous females apparently mature 

 in less time and have greater reproductive power than do the winged forms. 

 The fecundity of the winged hibernating females is not as great as that of the 

 wingless or the winged viviparous summer forms. 



"The pea aphis molts four times. An average of the lengths of the first 

 four instars, from 60 individual records, is as follows: First instar, 1.6 days; 

 second instar, 2.6 days; third instar, 2.8 days; fourth instar, 2.4 days; thus 

 making the average age at the time of the fourth molt, 9.G days. As might 

 be expected, the period of development was considerably shorter during the 

 warmer summer months than during the cooler periods in the spring and 

 autumn." 



Observations on the Life Histories and Habits of the Species of Aphids Most 

 Common on the Cultivated Apple (Mains mains) in Virginia (Blacksburg) 

 during the Season of 1915, including the oat aphis (Aphis avence), the rosy 

 aphis (A. sorbi), and the apple aphis, and a list of the more recent litera- 

 ture relating to these species, by M. T. Smulyan, are appended (pp. 64-75). 

 A. sorbi is apparently the most injurious of the three in Virginia and the apple 

 aphis probably the least. The author reports that his investigations of the 

 alternate or summer host plants of A. sorU in Virginia have substantiated the 



