28 



BULLETIN 1453, U. S. DEPARTMENT OF AGRICULTURE 



forestalled by the thickening and hardening of the skins of the larvae. 

 From these vermiform puparia only one adult emerged. The same 

 circumstances, in which the migrant larva is overtaken by the phe- 

 nomenon of pupation before it has reached a suitable location, prob- 

 ably account for the occasional puparia which are found in some- 

 what greasy situations upon pieces of infested meat. 



MIGRATION-PUPATION PERIOD 



The time which elapses between the end of the feeding period and 

 pupation is very short, often in warm weather only two or three 

 hours. In Table 10 it will be seen that 90 percent of the migrant 

 larvae pupated within 48 hours. These larvae were confined for 

 periods up to 24 hours within a greasy paper wrapper inclosing the 

 meat in which they developed. 



Table 10. — Migration-pupation records of mature larvae of Piophila easei at 

 Washington, D. C, in 1921 



Number of days after cessation of feeding 



Number 

 of larvae 

 pupated 



Number of days after cessation of feeding 



Number 

 of larvae 

 pupated 



1 and 2 _. - 



34,314 



3,053 



129 , 



40 



17 



9 



5 I 



6 ! 



10 



1 



3 .. 



11 



2 



4 -- .- 



15 



1 



5 



16. 



1 



6 



20 



1 



7 



Total 





8 



1 37, 579 



9 









1 In addition to the 37,579 larvae which pupated, 229 died without pupating, making a total of 37,8081arvae 

 used in the experiment. The migration records of these larvae are given in Table 1. 



The numbers of the puparia in Table 10 were estimated by means 

 of a chemical balance, it having been determined by .averaging a 

 number of weighed lots that well-nourished larvae form puparia 230 

 of which weigh 1 gram. Death without pupation occurred with 

 0.6 per cent of the larvae. 



MATAMORPHOSIS 



PUPATION 



Pupation occurs readily in such situations as dry earth, sawdust, 

 cotton, dust in floor cracks, and under boxes and sheets of paper, 

 Frequently migrant larvae partly or wholly enter empty skipper 

 puparia, where they transform. 



Having found a suitable place for pupation the larva contracts in 

 length, principally at each end, and increases slightly in girth, and 

 the skin rapidly changes from waxy white through buff and pink to 

 a rich coppery red. At first the head retains its mobility. Just at 

 this stage the larva, if disturbed, is able to relax and again become 

 active, but in a very short time a point is reached beyond which there 

 is no possibility of reversal of the pupation process. 



After the hardening of the skin of the last active stage of the 

 larva, which process forms the puparium, the insect becomes for a 

 brief period a prepupal larva. This is a sac-like transition stage. 



