June, '19] McCOLLOCH: HESSIAN FLY FLAXSEEDS 253 



although most of the writers recognize that a great variation exists. 

 Enochi (pp. 350-351) reports rearing flies from barley screenings that 

 had been held two years in dry surroundings. Marchal,^ in his work 

 in France, was able to rear six broods of flies in the course of a year. 

 He found that most of these broods were partial and that there was a 

 tendency for some of the flaxseed of each generation to hold over until 

 a latter generation. He advanced the idea that the species is perpet- 

 uated, in spite of the obstacles placed in its way by exterior conditions, 

 by the great variability of its biologic C3^cle. Webster (p. 261),' 

 quoting from Lindemann, says that the puparia (in Russia) are greatly 

 influenced by environment, temperature, etc., and this is probably 

 true of the other stages. Flaxseed collected by Lindemann in the 

 spring of one year lived over to the spring of the following year. How 

 far the number of these interlopers is augmented by a retarded develop- 

 ment of greater or less extent it is impossible to say, but that there is an 

 accession through this means there can be no doubt. Marlatt (p. 2)* 

 states that under exceptional conditions the insect may remain dor- 

 mant in the flaxseed state for a year or more and still bring forth the 

 adult, a provision of nature which is doubtless intended to prevent the 

 accidental extermination of the species. Webster (p. 11)^ says, " Under 

 exceptional conditions, such as in a dry room, flaxseed may be kept for 

 a year or, even two, but when moistened the flies will soon emerge. 

 So in the fields they will, during a drought, remain in the flaxseed state 

 for a considerable time after they would appear under normal condi- 

 tions, and only appear soon after rains have moistened the soil." 

 Numerous other writers make similar statements, but data on actual 

 rearings are very meager. 



During the past six years much of the writer's time has been spent 

 in a study of the life economy of the Hessian fly under Kansas condi- 

 tions. Numerous rearings have been made in the field, in the breeding 

 chambers of the air conditioning machine described by Dean and 

 Nabours,^ in the field insectary and from fly-infested material collected 



1 Enoch, F. 1891. The Life History of the Hessian Fly, Ceddomyia destntctor, 

 Say. Trans. Ent. See, London, for 1891, pp. 329-366. 



'^ Marchal, Paul. 1897. Les Cecidomyia des C6r6ales et leurs Parasites. Ann. 

 Soc. Ent. France, Premiere trimestre, 1-105. 



3 Webster, F. M. 1899. The Hessian Fly. Ohio Agri. Exp. Sta., Bui. 107, pp. 

 257-288. 



* Marlatt, C. L. 1900. The Hessian Fly. U. S. Dept. Agri., Div. Ent., Cir. 12, 

 pp. 1-4. 



•Webster, F. M. 1906. The Hessian Fly. U. S. Dept. Agri., Bur. Ent., Cir. 

 70, pp. 1-16. 



' Dean, G. A., and Nabours, R. K. 1915. A New Air Conditioning Apparatus. 

 JouRN. EcoN. Ent., 8: 107-111. 



