34 



BULLETIN 1453, U. S. DEPARTMENT OF AGRICULTURE 



Results of the foregoing rearing experiments show that the mini- 

 mum life cycle of the cheese skipper, when provided with juicy ham 

 as food for adults and larvae, is 12 days, the term " life cycle " being 

 here understood to include the preoviposition period. This brief 

 life cycle is divided about as follows: Preoviposition period, 1 day; 

 incubation period, 1 day; larval stage, 5 days; pupal stage, 5 days. 

 The majority of the insects which are produced in hot weather take 



a day or two longer, and it is safe to say 

 that two generations per month represents 

 the normal rate of summer increase at 

 Washington, D. C. , 



The method of rearing P. casei for life- 

 history data is shown in Figure 8. In 

 this vial one day's batch of eggs laid by 

 one female hatched into larvae which de- 

 veloped on juicy ham, migrated to the 

 cotton and pupated there. The resulting 

 adults died without reproducing on ac- 

 count of the advanced stage of drying 

 reached by the ham at the time they 

 emerged. This species thrives in close 

 confinement. 



INSECTS FOUND ASSOCIATED WITH 

 THE CHEESE SKIPPER 



Sakharov (67) has pointed out that the 

 cheese skipper when infesting brine-cured 

 fish has practically no competitors. The 

 same is also true . in the case of its 

 favorite food in this country — juicy, 

 newly cured ham. When cured meat be- 

 comes older, drier, and rancid, however, 

 various other sarcophagous insects appear 

 and the changes in the food medium 

 gradually render it unfavorable for skip- 

 per development. In general, a succession 

 of species (as suggested by Megnin (47) 

 and Stefani (71) with respect to cadavers) 

 attacks cured meat as changes take place 

 in its composition. The ham beetle (Ne- 

 crobia rufipes DeG.) prefers meat which 

 has been in storage for some time, and 

 the same preference is shown by the 

 larder beetle (Dermestes lardarius L.) 

 and certain tyroglyphid mites. Skipper 

 larva? in freshly cured meat are sometimes accompanied by maggots 

 of Lucilia sericata Meig. (fig. 5, 5), and probably other blowflies. 



In stores of bones the skipper is usually present, but in such 

 locations the species may be at a disadvantage both because of 

 the condition of the food supply and because of the abundance 

 of a number of other scavengers, several of which are predacious. 

 Skippers in heaps of bones have been found by the writer and 



Fig. 8. — Vial used in studying 

 the life history of Piophila 

 casei, showing dead adult 

 progeny resulting from one 

 day's eggs laid on ham by one 

 female. Pupation occurred in 

 the cotton plug and emergence 

 took place after the food was 

 too dry to permit further re- 

 production 



