254 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 12 



in the field. It is not the purpose of this paper to go into detail con- 

 cerning the experimental work, since it is planned to present the com- 

 plete studies in bulletin form at some future time. Certain points, 

 especially with regard to the length of the flaxseed stage, seem to be of 

 enough importance to warrant publication at this time as they have a 

 direct bearing on the control of this insect. 



The results of these studies show that the length of the various 

 stages of the Hessian fly are extremely variable and consequently 

 there is a great variation in the length of the liffe cycle. The exact 

 length of the life cycle has been determined for over 900 individuals 

 and the approximate length has been found for 8,500. While varia- 

 tions have occurred in each stage (Table 1), the greatest difference has 

 been in the flaxseed stage where it has ranged from 7 days to 1,083 

 days. The minimum life cycle of 20 days was obtained under a 

 constant temperature of 70° and humidity of 70 per cent, while the 

 maximum cycle of 42 months was the result of studies in the field in- 

 sectary and rearings from infested material kept in emergence boxes. 



Table 1. Showing the Extremes of the Life Cycle 



Stage Maximum Minimum 



Egg 12 days 3 days 



Larva 182 days 9 days 



Flaxseed 1,083 days 7 days 



Adult 6 days 4 hours 



Life cycle 1,283 days 20 days 



In order to determine the length of the flaxseed stage, under field 

 conditions, clumps of infested wheat or stubble were collected at all 

 seasons of the year from various localities of the state and placed in 

 pasteboard rearing boxes. Each box had at least one glass tube into 

 which the flies were attracted by the light on emerging. These boxes 

 were kept in the field insectary under practically natural temperature 

 conditions. The moisture, however, varied from that in the field. 

 The material was thoroughly moistened when placed in the boxes. It 

 was also moistened three times during each year: (1) in the spring 

 when the first spring rains occurred ; (2) in midsummer, and (3) in the 

 fall when the fall rains began. Being of pasteboard, the boxes also 

 absorbed some of the atmospheric moisture and they were also subject 

 to wetting by beating rains. In all, over 150 collections of infested 

 material have been under observation, and most of the material has 

 been held for at least three years before being discarded. 



While the data obtained in such an experiment can only be approxi- 

 mate, it has yielded some very interesting results. The fact that this 



