220 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 4 



On eighteen leaves taken at random there was found to be an average 

 of 62+ eggs on the upper sides and 115+ on the lower sides. On six 

 leaves taken from a badly infested field there was an average of 293 + 

 eggs to the leaf, the highest number on any one leaf being 343. Leaves 

 bearing eggs were collected in the fall and kept outdoors under as natu- 

 ral conditions as possible to determine what per cent of the eggs would 

 hatch. Under these conditions it was found that 76 per cent of them 

 hatched when brought into the insectary in March. Whether all of 

 the eggs thus collected were fertile or not we had no means of knowing. 

 On the other hand, a known number of fertilized eggs were kept under 

 natural conditions outdoors and all of these hatched the follo^\dng 

 spring. Eggs deposited on October 15 and 16 hatched in the field on 

 March 30, thus giving five and one-half months as the period of incu- 

 bation. The spring of 1910 was earlier than usual, however, and likely 

 hatching occurred somewhat earlier than in ordinary seasons. 



On April 1, 1910, the newly hatched stem-mothers were found 

 present on the stumps of cabbage left standing in an infested field from 

 the fall before. The field had been plowed ; but many of the long stumps 

 were left with their tops projecting and these had begun to send up 

 new growths. In the centers of these new growths among the tender 

 leaves, stem-mothers were found in abundance. The number was 

 counted on five different plants and ran four, eleven, thirty-one, 

 five and nine respectively. In another infested field not plowed, but 

 in which the stumps had remained undisturbed, the aphids were 

 found in varying numbers. From these stem-mothers we have reared 

 up to the present time, December 3, 1910, twenty-one generations of 

 agamic wingless females. The average length of each generation has 

 been 11 4-5 days. 



During the summer, generations of winged forms are produced, 

 especially on crowded plants, and these serve to distribute the aphis 

 to different plants. 



Hibernation 



In the warmer climate of the Southern States the cabbage aphis 

 undoubtedly remains on the plants in the adult condition the season 

 through. They have been observed all through the winter on cabbages 

 at Agricultural College, Mississippi. In Florida, Quaintance says the 

 mildness of the winter often allows the agamic females to carry the 

 species through the year. It is doubtful if the adults can survive the 

 winters of New York State. 



Several plants infested with aphides were set beneath cages covered 

 with cheese cloth and frequent observations made on the effect of the 

 lowering temperatures. The insects throve and multiplied during 



