OBSERVATIONS ON BLOW FLIES; DURATION OF THE 

 PREPUPAL STAGE AND COLOR DETERMINATION. 



PHINEAS W. WHITING. 1 



The results of two main lines of experiment upon blow flies 

 are recorded in the following paper. The first was concerned 

 with the duration of the prepupal or migration stage of the larvae 

 and the conclusions may be summarized as follows: 



The length of the prepupal period is determined by environ- 

 mental rather than by hereditary factors and these factors are 

 both complex and obscure. In general, dryness, cold, or agita- 

 tion due to crowding, tend to prevent pupation, while change 

 from dryness to dampness or the reverse, induces pupation. The 

 prepupal stage may be extended for a long period, four months 

 in one experiment (igi2-f), in warm temperature without injury 

 to the development of adult flies, which emerge from the pupae 

 in normal condition. Lack of opportunity for the larvae to bury 

 themselves does not inhibit pupation. Exhaustion of the food 

 supply before the larvae have attained full size has a tendency 

 to produce undersized but normally formed flies. The causes 

 producing misshapen and imperfectly expanded flies are more 

 obscure, but may be in part due to drying of the pupae. Delayed 

 pupation in Lucilia larvae is evidenced by a change from white to 

 pink in the fat bodies, but in two genera of larger flies, Cynomyia 

 and Calliphora, the white color is maintained although consider- 

 able shrinkage of the whole body occurs. There is no evidence 

 that overfeeding delays pupation, but much evidence that larvae 

 will pupate immediately despite the fact that they have had 

 abundant opportunity to overeat. 2 



1 Contributions from the Entomological Laboratory of the Bussey Institution, 

 Harvard University. No. 76. 



2 From his studies on blow flies, Herms (Herms, Wm. B., '07, "An Ecological 

 and Experimental Study of Sarcophagidae with Relation to Lake Beach Debris," 

 Jour. Exp. Zool., IV., i) reaches the conclusion that an optimum of development is 

 attained by the larvae after a certain period of feeding and that continued feeding 

 after this has a tendency to delay pupation. In many of my cultures, however, 



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