132 



THE EEPORT OF THE 



No. 36 



TABLE 1. — Autumn Fly Emergence. 



Fly Emergence in the Field. 



Liasmuch as the records given in Table 1 might have been influenceid by un- 

 natural conditions resulting from laboratory arrangements, the important point 

 was to determine whether or not the same conditions were occurring in the field 

 under strictly natural conditions. It was clearly proved that flies will emerge from 

 September puparia under laboratory conditions, and, as will be seen later, eggs 

 were being taken freely in the field. Hence it was probable that flies were emerg- 

 ing freely from the soil in the field. In order to determine this point careful 

 examination of the roots of old cabbage plants was made. The roots were cut and 

 the soil worked over to the depth of 6 inches. This was done on September 28th, 

 29th, 30th, and it was found that out of 78 plants examined, 48 plants were or 

 had 'been infested. 30 plants did not show any sign of attack, and no puparia were 

 taken. From the 48 plants, however, were found : 



124 empty puparium cases from which flies had emerged. 

 96 sound and apparently healthy puparia. 

 14 large maggots more than 3 mm. long. 

 4 small maggots less than 3 mm. long. 



Close examination for minute forms was not made, the important point being 

 indicated that many flies were emerging in the field. It is hardly fair to claim 

 a ratio between the empty puparium cases taken in the field with those under 

 observation in the laboratory, because we could not be sure when the files did 

 emerge. However, the fresh nature of the puparium cases leaves no room for doubt 

 that files emerge freely from the soil during September. 



