February, '15] BISHOPP-DOVE-PARMAN: HOUSE FLY BIOLOGY 



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in our breeding experiments ranged from eight days to fifty-one days. 

 A much longer period was observed in hibernation experiments at 

 Dallas and Uvalde, Texas. In one of these tests at Dallas a com- 

 Mned larval and pupal period of six months was observed and in the in- 

 stance at Uvalde larvae and pupae put in a box with the manure in 

 which they were breeding on December 13, 1913, produced some adult 

 flies as late as April 4, 1914, a period of one hundred and twelve days. 

 The amount of manure was not sufficiently large to generate heat, but 

 protected the stages from extreme cold. No doubt during the coldest 

 iveather development was completely arrested. 



The data appertaining to a number of the tests to determine the 

 •developmental periods are given in Table No. 2. In most of these 

 tests a comparatively small amount of breeding material was used in 

 •order to observe the stages more closely. Hence these periods, espe- 

 cially the larval, are in general rather longer than would occur under 

 favorable natural conditions. 



Egg Stage. — The exact incubation period was determined in only 

 a few instances. In practically all cases it was found to be less than 

 twenty-four hours even in winter. When eggs are deposited on manure 

 piles of considerable size the temperature experienced by them is much 

 above the air temperature during cool weather, and this accounts for 

 the short periods observed in winter. When eggs are separated from 

 the mass of manure the period is greatly lengthened during cool 

 weather. This is well illustrated in two of the lots upon which data 

 are given in Table No. 2. In one case, eggs deposited on January 14, 

 1914, hatching of those left on a manure heap took place in less than 

 seventeen hours, while part of the same lot kept in the laboratory on a 

 small lot of manure did not begin hatching until forty-one hours after 

 deposition, and was not complete till eight hours later. 



Larval Stage. — The larval stage was found to vary in length from 

 three and one-half days to about three weeks. In a hibernation test 

 where the manure was not in a fermenting condition the lar^^al stage 

 was observed to persist for nearly four months. In one case a period 

 of a little less than three days was observed. The usual time required 

 from hatching to the formation of the first pupae during warm weather 

 was from four to seven days. The temperature materially affects the 

 larval period but the character and particularly the amount of the 

 breeding medium was found to be of still greater importance as factors, 

 imder natural conditions. By character we refer to the kind of mate- 

 rial, the am.ount of m.oisture it contains, and the degree of fermenta- 

 tion. In large piles of manure it was observed that to a marked extent 

 the larvae govern their temperature conditions by penetrating farther 

 into the manure during cold weather and remaining nearer the surface 

 when the weather was warm. 



