THE CHEESE SKIPPER AS A PEST IN CUBED MEATS 



39 



Table 16. — Results of immersing migrant larva of Piophiia casei in various 



liquids — Continued 



Liquid used 



Duration 

 of 



immersion 



Conditions found in pill boxes 

 after all emergence had been 

 completed. All insects 

 dead 







Adults 



Puparia 



Larvae 





Hrs. 



Min. 



30 



~~~30~ 



"""is" 



% 



1 



""20" 



5 

 12 

 34 



1 



9 

 8 

 1 

 

 5 

 2 

 5 

 1 

 

 4 

 5 

 3 

 6 



10 

 4 

 4 

 4 

 4 

 

 

 2 

 

 6 

 

 3 

 1 

 4 



1 



Do 



Do 



Do 



Do 



Do 



1 



1 

 2 

 3 



24 



2 



2 

 2 



8 

 11 

 4 



Do - 





4 



Carbon disulphide __ -....- 









Do . 





5 



Do... ....'. 



24 



9 





7 



Ether . - ... 





5 



Ethvl acetate -. - 





5 







2 













The remarkable resistance of these maggots is attributed by Ales- 

 sandrini (4) to (1) the nature of the cuticle, (2) the closure of the 

 spiracles, (3) the amount of air held in the body and the diminished 

 consumption of oxygen due to the immobility which they usually 

 assume shortly after immersion, (-4) the large quantity of reserve 

 food in their bodies. Crawford (15) has furnished an interesting 

 account of similar resistance by the larA^a? of the ephydrid fly Psilopa 

 vetrolei Coq., which inhabit pools of crude petroleum. 



LOW-TEMPERATURE EXPERIMENTS 



Cold storage of meat is, of course, a reliable preventive of infesta- 

 tion, and the writer's experiments indicate that cold will kill all 

 stages. The results of the low-temperature trials were irregular, 

 but it is certain that speedy killing effects with cold-storage tempera- 

 tures not well below freezing can not be expected. In the earliest 

 known reference to this species (1567) Olaus Magnus (4j6, p. 812) 

 referred to the resistance of the larva? to cold. Murtfeldt (53, p. 174) 

 asserted that '* severe and protracted cold " kills all stages, and 

 Sakharov (67) found that activity ceases at 8° C. (46.4° F.) and 

 that the lowest temperature at which reproduction takes place is 

 13° C. (55.4° F.). The latter reported that larva? survived-22° C. 

 (—7° F.) for two weeks. 



Oviposition trials in the laboratory resulted in the deposition of 

 eggs by flies exposed to artificial temperatures which ranged from 

 06 to 62° F. 



The experiments which follow show the ability of P. casei to resist 

 cold. 



In an ice refrigerator at 48 to 50° F. — The growth of the larva? is 

 suspended by temperatures of from 48 to 50° F., but under these 

 conditions some migrant larva? are able to pupate, and many of these 

 pupa? produce adults and pupation is prolonged by several weeks. 

 Eggs are not laid at these temperatures, and eggs placed in the 

 refrigerator do not hatch. Adults are feebly active. In the case of 

 15 newly emerged adults placed in the refrigerator deaths began on 



