68 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



up entirely of viviparous females, as no sexes have so far been observed 

 in the fields or in the cages. The farthest north in Texas that observa- 

 tions were made on this species was AVichita Falls, just south of the 

 34th parallel. It is evident that at this point sexes do not occur and 

 the viviparous females survive the winter. Mr. Davis has written 

 that the sexes have not l)een found in their search at West Lafayette, 

 Indiana. 



At College Station the winter temperatures are seldom low enough 

 to prevent reproduction, though the daily number of young produced 

 is very small. There are a few days when the lice, especially the old 

 ones, do not reproduce. At Wichita Falls the winter temperatures 

 of 15 to 20 degrees F. are not uncommon and frequently the tempera- 

 ture may remain below 32 degrees F. for five to seven days at a time. 

 Often during the cold spells as much as one inch of snow may remain 

 on the ground for a few days. Under such conditions the lice do not 

 reproduce but reproduction takes place when the warm temperatures 

 prevail. But few lice succumb to the cold at this point, these being 

 the very old lice. At Brownsville, near the 26th parallel, the condi- 

 tions in January are similar to those which exist at College Station 

 in October. The daily young produced in the fields is four to six. 



With the approach of the hot, dry weather of the summer there is a 

 'decided reduction in the daily young produced and all stages in the 

 life-history are lengthened, the same as under winter conditions. It 

 is quite evident that the summer conditions in Texas are even more 

 trying than the winter. There are four to five months of very un- 

 favorable conditions during the summer. 



In 1914 a first-born generation series was started on January 18 

 and continued until August 6. During this time twenty generations 

 of lice were born. This work was started again on September 14, 

 1914, and continued until the same date in 1915. During this period 

 of exactly twelve months, thirty-five generations of lice were born. 

 The average total young produced by the generations of the first 

 series was 80, by the second 93. 



Two other species of aphids were found to feed on the same host 

 plants as the turnip louse. These are the cabbage louse and the 

 "garden aphis," or green peach aphis, Myzus persiac Sulz. Often 

 one or both of these species might be found feeding on the same plant 

 with the turnip louse, sometimes the colonies of the two species 

 would over-lap. Both of these species have been confused with the 

 turnip louse, even by entomologists. The cabbage louse was most 

 often found on cabbage, but in the spring of 1915 it was common in 

 the flower heads of mustard and turnip. From the observations made 

 in this study it could be said that the turnip louse is most generally 



