121 



H. illucens. Thus, the two species developed in separate locations in 

 the same cups with little chance of coming in contact. 



A situation such as this was seen in the field at the tilling site 

 (Figure 31). Chips had been added to very wet manure which, when tilled, 

 was ca. 29 cm above the level of the walks. A definite moisture gradient 

 existed in the chips-manure mixture. Deep in the manure, at the level 

 of the walks, there was a large population of soldier flies. Mear the 

 top of the manure-chips mixture, 2 to k cm beneath the surface, was a 

 large house fly population. The populations of the two species were 

 separated vertically by 25 to 27 cm and neither could be detected with- 

 out digging into the manure. This was an unusual situation created by 

 the depth of the manure-chips mixture and the moisture gradient within. 



Results of studies with Hermetic, illucens and Saraophaga robasta. 

 In treatments k and 5, where both species were reared together, the 

 mortality of S. robusta larvae was increased significantly, but the 

 mortality of H. illucens was not significantly affected (Table 19). 



Since the larvae of S. robusta require only 3 days to complete 

 their larval development, the reduction in their population by H. 

 illucens was not expected. Because larvae of S. robusta and H. illucens 

 prefer media similar in moisture content, it is possible that the 

 bottoms of the cups of medium were the sites preferred by both fly 

 species. Sarcophaga robusta may have been unable to compete success- 

 fully with H. illucens for the preferred sites and was displaced in 

 numbers reflected by the increases in mortality shown in Table 19- 



