1 62 Journal of Agricultural Research voi. xiii, No. 3 



The fatal temperature is thus shown to be quite low, and the fact that 

 many revive after exposure to temperatures as low as 22° ^. explains 

 why flies persist outdoors in this latitude as late as the first week in 

 December. The most important point is that flies will resume activities 

 when the temperature is raised, even after exposure to rather low tem- 

 peratures. There is no hibernation in the sense of long-continued sus- 

 pension of activity during the winter months. Dove (5) states that he 

 has never — 



observed living adults to remain quiescent for more than a few days. The natural 

 heat of the sun or very slight artificial heat will cause them to become active. 



OVERWINTERING OF LARVA AND PUPA STAGES 



Probably every observer who has planned any work on this problem 

 has started out with the assumption that "it might reasonably be thought 

 that the pupse would prove more resistant than the earlier stages" 

 (5), and there have, in fact, been many attempts to carry the puparia 

 of the house fly through the winter. "But," says Copeman, "so 

 far as I am aware, no observer has succeeded in breeding out the 

 flies from pupse kept through an average winter in this country" [Eng- 

 land]. "Nor," according to Hewitt's statement (9), "has it ever been 

 possible in my breeding experiments in Canada and in England to carry 

 the insect through the winter in the pupal state." Lyon (14) reports 

 some experiments started on October 19, 191 4, at Boston, Mass. Thirty- 

 seven lots, of 100 puparia each, were buried in w^et and dry sand, wet and 

 dry loam, wet and dry horse manure, and leaf mold. These materials, 

 with pupae, were placed in glass jars, some in the basement of a stone 

 building, some in an unused greenhouse, some in sheltered positions 

 outdoors, and some in exposed positions outdoors. No flies emerged 

 from those lots placed outdoors. Several hundred emerged from these 

 kept in the greenhouse and in the basement, but even from these none 

 emerged after December i, 1914. Upon examination on June 23, 1915, 

 the pupae appeared normal, but on being broken open they were found 

 to have completely dried out. 



The writer has tried similar experiments and obtained similar results. 

 About 1 3^ quarts of pig-manure-bran mixture containing approximately 

 900 puparia were collected at Bethesda, Md., on November 14, 1914. 

 This mass was put in a large wooden box, covered with 3 or 4 inches of 

 sand, and the box, covered with a plate of glass, \vas placed on a shelf 

 of a screened insectary. House flies in considerable numbers emerged 

 on mild days up to December 4. None emerged after that date. On 

 March 17, 191 5, the box was transferred to a warm room in a green- 

 house and remained there until April i , but no flies appeared. Another 

 collection of pupse made on December 3, 1914, and handled in the same 

 way^ also showed no emergence after December 4. In a third experiment 

 special precautions were taken to prevent freezing, and pupae of known 



