June, '14] HEWITT: HOUSE-FLY CONTROL WORK 283 



choice there are two alternatives, namely, either to count the number 

 of dead as compared with the living larvae in the treated manure, or 

 to count the flies emerging after treatment. In previous work of this 

 nature the former standard has been employed as a rule. It has a 

 serious defect, however, namely, that the portion of treated manure 

 selected, presun*iing a fair amount has been treated, may not be typical 

 of the whole; in fact my experiments have shown that it would be 

 extremely difficult if not impossible to select an average sample. To 

 this point I shall refer later. In my opinion the only satisfactory 

 basis of comparison is the number of adult flies which emerge from the 

 whole amount of the manure treated. The experiments about to -be 

 described were arranged with that object in view. 



Methods 



It was decided to use a cubic yard, that is twenty-seven cubic feet 

 of manure, as the amount of manure to be treated and the num- 

 ber of flies emerging from a cubic yard of untreated manure would 

 be used as the standard of comparison. As experience demon- 

 strated the actual quantity of manure was a little less than tw^enty- 

 seven cubic feet owing to the sinking of the manure. In spite of the 

 cubic yard being heaped up it settled to a depth at the sides of two 

 feet six inches on the average, thus giving approximately twenty-two 

 cubic feet of manure after settling. 



To contain the manure w^ire enclosures (Plate 9) were constructed 

 of strong one-inch galvanized poultry wire supported- by wooden stakes 

 and cross-pieces at the top which was open. The stakes were driven 

 into the ground until three feet of wire remained above ground. 



The horse manure, which was mixed with an average quantity of 

 straw used in the stables, was carted straight from the stable and 

 thrown into the wire enclosures and trodden do\^^^ as it was throwm in 

 to obtain a fairly compound and tjq^ical manure heap. The top 

 of the pile was made higher than the enclosure to allow for the settling 

 which took place in spite of the packing. The sandy soil was piled up 

 around the base of each heap to provide accommodation for the pu- 

 pation of the larvae. 



Six such piles of manure were used. In some cases they were left 

 for two days to allow the flies to oviposit, in other cases, for example, 

 where chloride of lime was used, they were treated immediately after 

 the enclosures had been filled. After exposure for two to three days 

 and treatment with the insecticides the heaps were covered with. 

 wooden covers as shown in plate 9. These covers were made suffi- 

 ciently large to leave a space of about six inches all around the wire 

 enclosures w^hen they were covered. Two holes were provided in the 

 top for wire balloon fly traps to capture the flies as they emerged. 



