THE CHEESE SKIPPER AS A PEST IN CURED MEATS 



21 



flies shown in Table 8, 463 were males and 401 were females. Of 

 2,112 other flies observed (Table 9), 1,074 were males and 1,038 were 

 females. These flies composed the entire progeny of females which 

 laid eggs on ham in vials, each day's eggs of each individual being 

 kept separate. 



DEVELOPMENTAL PERIODS OF THE SEXES 



Emergence records consistently show that the females take longer 

 to develop than the males. Data to support this conclusion are 

 detailed in Table 14 and also in Table 9 which follows : 



Table 9. — Comparative rate of emergence of the sexes of Piophila casei 1 

 at Washington, D. C, in 1921 





Number emerged on— 





Sex 



1st 



day 



2d 



day 



3d 



day 



4th 

 day 



5th 



day 



6th 

 day 



7th 



day 



8th 

 day 



9th 

 day 



10th 

 day 



11th 

 day 



12th 

 day 



13th 

 day 



14th 

 day 



15th 

 day 



Total 



Male 



Female .. 



258 

 18 



437 

 233 



127 

 351 



145 



65 

 82 



36 



84 



23 

 38 



19 

 22 



22 

 25 



8 

 17 



7 

 12 



2 



9 







1 



1 

 







1 



1,074 

 1,038 



1 Emergence of adults resulting from daily batches of eggs laid by isolated females. Each batch of eggs 

 was allowed to develop in a separate vial. The flies which emerged first in each vial are recorded under 

 "1st day," the entire series being consolidated as though the beginning of emergence in all the vials had 

 been simultaneous. 



The rather long developmental periods of some of the insects re- 

 corded in Table 9 are explained by the condition of the food supply. 

 These records were made in warm weather, when the first and last 

 emergence of adults from a given day's eggs would have extended 

 over only four or five days, if the larvae had invariably had access to 

 a plentiful supply of moist food. 



BEHAVIOR OF ADULTS 



The adult flies are usually eager, when confined in small glass con- 

 tainers, to move upward and toward the light — responses which 

 facilitate handling them. These two responses are not particularly 

 strong in flies which are flying freely in a room, however, and the 

 flies are not strongly attracted to the windows, as might be expected. 

 Unconfined flies respond principally to the stimulus of food odors. 

 Jars containing cheese or meat, especially if these are infested with 

 the maggots and have a decided odor, are foci for the free adult 

 skippers in the room. Females may sometimes be observed running 

 about over the muslin covers of the jars, feeling for apertures with 

 their ovipositors. By placing an inverted cone in the opening of 

 jars containing cultures of the larvae in ham, it has been possible in 

 the laboratory to trap numbers of the flies. 



Newly emerged adults are especially attracted by odors of their 

 foods, and it was found difficult to remove adults from a large ham 

 riddled with galleries of the larvae. Rather than take flight the flies 

 preferred to dodge down into the dark interior of the meat. At an- 

 other time it was found almost impossible to remove adults from a 

 paper can, which contained thousands of puparia, both normal and 

 empty. The attraction of the dark interior of this can was almost 

 irresistible to the flies which had emerged in it. 



