June, '19] 



McCOLLOCH: HESSIAN FLY FLAXSEEDS 



255 



material was collected in the field makes it impossible to know the age 

 of the flaxseed at the time they were included in the experiment, and 

 the data are, therefore, summarized, in Table 2, to show the number of 

 days between collection and emergence. Flies to the number of 7,461 

 were reared from this collected material and the average time between 

 collection and emergence was 113.2 days, with extremes of 2 days and 

 1,083 days. It will be noticed that 5,114 flies, or 68.4 per cent, 

 emerged during the first month, and 7,385, or 98.9 per cent, during the 

 first year. On the other hand, 1.1 per cent of the flies did not emerge 

 until after the first year, although they were subjected to the same 

 conditions. If such conditions prevail in the field, and 1 per cent of the 

 flaxseed hold over from one to three years, it serves to explain the 

 sudden appearance of the fly in some areas where it was thought to be 

 eliminated, and it emphasizes the importance of taking care of all 

 stubble fields. Experiments are now being conducted to determine 

 whether the fly does hold over for such long periods in the field. Thus 

 far flies have been reared in fairly large numbers from stubble that has 

 stood undisturbed for eighteen months in the field. Living flaxseed 

 are still to be found in this stubble, indicating that further emergence 

 may occur during the spring of 1919. 



Table 2. Showing the Period Between Collection and Emergence of Flies 



Note: On May 7, 1919, the writer reared a female Hessian fly from a clump of 

 wheat collected May 8, 1915. Allowing approximately a month for the flj- to reach 

 the flaxseed stage, this gives a life cycle of at least 49 months. 



