98 

 GENERATIONS OF THE BOLLWORM. 



It has long been stated that the number of generations annually of the 

 bollworm in the cotton belt varies from about four in the more north- 

 ern part to six or even seven in the extreme southern part. It does 

 not appear, however, that this statement is based on actual breeding 

 experiments, but rather on the result of field observations. Conclu- 

 sions regarding this matter based solely on field observations are some- 

 what unsatisfactory, as they are apt to be spread over a wide terri- 

 tory and to be complicated by variations in climate and environment, 

 as well as by the fact that the broods are confused on account of the 

 long period of emergence of the moths in the spring. This causes the 

 period of spring oviposition to be lengthened, so that long after the 

 majority of boUworms are well grown others are still in the egg 

 stage. These supplementary generations persist throughout the sea- 

 son, and, although numerically unimportant, are apt to lead to con- 

 fusion regarding the principal ones. 



As the question of the number of generations is one of importance, 

 effort has been made to secure as much data on the subject, confirma- 

 tory or otherwise, as possible. In 1903 attempt was made to secure 

 information on this point by ascertaining, for different localities of 

 the cotton belt, the periods of maximum oviposition of the moths 

 during the season. It was thought that these egg records for the 

 season, when plotted, would indicate approximately the periods of 

 greatest abundance of the moths, thus marking the respective genera- 

 tions. Theoretically such data would undoubtedly furnish the infor- 

 mation desired, but in practice many factors were found to enter into 

 the making of trustworthy records, such as variations in the age of 

 the corn used in making counts, the character of the weather, etc., so 

 that little may be safely inferred from the egg records obtained. It 

 is proper, however, that acknowledgment be here made of the assist- 

 ance received in this work from Dr. W. R. Shaw and Mr. A. C. Lewis, 

 of the Oklahoma Agricultural Experiment Station; Mr. Mark Riegel, 

 Pomona, Ga. ; Prof. H. A. Gossard, of the Florida Agricultural 

 Experiment Station, and the late Mr. G. H. Harris, of this Department. 

 The records made by Mr. Riegel and by Mr. Harris are presented 

 under the caption "Oviposition on corn" (p. 42), to which the reader 

 is referred. 



At the beginning of the season of 1904 it was decided to carr}^ a 

 series of consecutive generations through the entire summer under 

 natural field conditions. This work was conducted in a large field 

 cage placed in a lot adjoining the laboratory at Paris, Tex. The cage 

 consisted of a solid framework 15 feet long, 12 feet wide, and 8 feet 

 high, covered with ordinary black window screen and provided with a 

 small door on the side. (See PL XVII.) In it were planted two lots 



