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Vol. XLIII. LONDON, MAY, 1911. No. 5 



OBSERVATIONS ON MITES INFESTING THE HORN FLY, 

 H.^MATOBIA SERRATA ROB. DESV. 



BY DR. SEYMOUR HADWEN, OTTAWA, ONT. 



The mites were first observed on July 3rd at Duncans, British 

 Columbia. My attention was drawn to them by seeing several specimens 

 of Hcematobia serrata Rob. Desv., which appeared to have been powdered 

 with brick-dust ; on looking more closely I found that they were heavily 

 infested with mites. Out of ir8 flies captured I found 94 infested with 

 mites, but as mites were seen travelling from one dead fly to another it 

 was difficult to arrive at a positive determination. This estimate was made 

 with the aid of a hand lens ; the number found on each fly varied ; some 

 had 4, 5, others were covered. 



Later I found the mites in other parts of British Columbia. This 

 occurrence, coupled with the fact that H, serrata does not seem to have 

 been such a serious pest during the past summer (19 10), as it usually 

 is, suggests to my mind that the mite may prove to be detrimental 

 to the fly. 



On one farm I visited frequently during the summer, who the owner 

 had been spraying his cattle said that the spraying had diminished the 

 number of flies. He was asked to stop spraying for a time, and no 

 apparent increase was noted. 



On communicating with Mr. N. Criddle, of Treesbank, Manitoba, I 

 learned that H. serrata in that locality did not appear to be infested with 

 mites. 



Some living infested flies were shipped to Mr. Criddle, but arrived 

 dried up and dead. No further attempt was made to try and infect clean 

 flies in a new locality. 



The introduction of H. serrata into British Columbia dates back 

 some years. I find a record of a specimen taken by Miss Ricardo at 

 Vernon in July, 1902. 



