30 



BULLETIN 1453, U. S. DEPARTMENT OF AGRICULTURE 



Table 11 shows to what extent hot weather shortens the meta- 

 morphosis. The first group, including flies which emerged from 

 May 10 to June 19, experienced moderately warm temperatures, 

 whereas the group of flies which emerged from June 20 to July 16 



were exposed to hot weather during their 



pupal stage. 



tion data. 



Table 12 includes other pupa- 



EMERGENCE OF ADULT 



By vigorous use of the balloonlike ptilinum 

 the insect forces off the dorsal half of the 

 anterior tip of the puparium. This some- 

 times falls away, but more frequently opens 

 as on a hinge and returns to its normal 

 position after the escape of the fly. Often 

 the dorsal and ventral halves of the anterior 

 end of the puparium are both broken off 

 during the fly's struggle for liberty. 



The emerging fly, shown in Figure 7, 

 rapidly becomes darker as its exoskeleton 

 hardens. The use of the ptilinum may be 

 observed when newly emerged flies are trying 

 to escape from a vial plugged with cotton. 

 The organ is greatly expanded, the force of 

 the expanding fluid being such as to affect 

 the whole head, displacing the eyes laterally 

 until their inner margins are separated by 

 an interval greater than the width of the 

 thorax. The insect then uses its legs to 

 push the thorax against its head, in a 



supreme effort to escape, the process being comparable to the driving 



of a wedge. 



LIFE CYCLE 



Fig. 7. — Adult of Piophila 

 casei showing appearance 

 during the act of emerg- 

 ence. X 10. Part of 

 the puparium has been 

 removed. The ptilinum 

 is here shown at nearly 

 maximum expansion and 

 the pressure of the body 

 fluids has temporarily 

 greatly increased the size 

 of the head 



« 



Table 12 summarizes available information from literature in 

 regard to certain aspects of the biology of the cheese skipper, in- 

 cluding facts brought out in this bulletin. 



