1922] Larrimer: Delayed Emergence of Hessian Fly 



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It may be noticed that the crest of the pupation curve on 

 October 11, did not reach one hundred, indicating that approx- 

 imately forty per cent of the larvae did not pupate during the 

 time covered by the graph and subsequent examinations 

 proved that they passed the winter in the old summer stubble. 



During the spring of 1921, from pupation records made as 

 previously explained, it was determined that pupation of these 

 "hang-over" larvae began March 17 and was practically 



Fig. 2. Map indicating the approximate dates of emergence of the "late wave" 

 of Hessian ?Ly in October, 1920. 



completed by April 10. Emergence of adults from these 

 pupae began March 29 and continued throughout the month of 

 April. A very few healthy larvae failed to pupate, but these 

 were so very hard to find in the field that further observation 

 on them was not practicable. 



Pupariation is a term that it has been found convenient to 

 apply to that activity by which the larvae of Hessian fly change 

 to the flaxseed stage, as distinguished from actual pupation. 

 Pupariation records were made on the larvae, offspring of the 

 late wave, in order to determine the condition in which they 

 entered and passed the winter. At frequent intervals 100 



