June, "15] 



BISHOPP: FLIES WHICH CAUSE MYIASIS 



325 



cumbed to the disease are soon covered with swarms of flies which feed 

 upon the excreta, blood, etc., and then pass to wounds on other animals 

 where infection may be produced by bacilh carried on the legs and 

 body or by regurgitation of the germ-laden food or possibly by excre- 

 ment. Thousands of flies develop in the carcasses where they are 

 not properly disposed of and there is a strong probability of the result- 

 ing flies being capable of conveying the virulent organisms to healthy 

 animals. 



Summary of Life-History and Seasonal History of Some of the 

 Species of Flies which Produce External Myiasis in the 

 United States. 



Mr. E. W. Laake, working under my general direction, at Dallas^ 

 Texas, is responsible for most of the notes on the life-histories from 

 which the following summaries have been made. Work along similar 

 lines was conducted by Mr. J. D. Mitchell at Victoria, Texas, and 

 by Mr. D. C. Parman at Uvalde, Texas. 



Chrysomyia macellaria. — The method of wintering of this species has 

 not been definitely determined. In our hibernation experiments with 

 adults and immature stages we have been unable to carry the species 

 through the winter. This, and other points, indicates that the species 

 normally dies out in the winter except possibly in the extreme southern 

 portion of the United States, and in the tropics, and the reinfestation of 

 the country progresses as the season advances. The species appears 

 shortly after settled w^arm weather begins in the spring and the number 

 usually increases until frosts in the fall. Often a partial checking of 

 the ravages of the species occurs in midsummer, especially when the 

 weather is hot and dry. The first infestations of live stock are found 

 usually in May, and September and October are as a rule the months of 

 greatest injury. In western Texas, where the rainfall is normally 

 small, the years with abnormally heavy rainfall are generally the most 

 productive of screw worm infestations. 



The period from emergence of adult flies to deposition of eggs ranges, 

 as observed by us, from three to eighteen days. As many as eight 

 consecutive depositions by one fly have been observed to take place, 

 the period between depositions being from one to seven days. Under 

 the best conditions it seems that the depositions may occur at inter- 

 vals of two to four days. The number of eggs deposited in one batch 

 appears to vary from forty to two hundred forty-eight, and the greatest 

 number recorded from one female was twelve hundred twenty-eight. 

 The larvae hatch within a few hours. Pupation occurs from six to 



