PARASITES OF FLIES 243 



wings of the male appear to be non-functional. The parasite 

 apparently attacks only the puparium, and that only after it has 

 been formed for about twenty-four hours, and a number of them 

 issue from the same puparium." They found that one female was 

 able to parasitize twenty-two puparia, and another one sixteen. 

 The average life-cycle was about twenty-two days. The 

 parasite seems to hibernate as a full-grown larva in the 

 puparium. In some of their observations they found that 90 "/o 

 of the puparia they examined were infected. 



Girault and Sanders also studied two other species, PacJiy- 

 crepoidetis dubiiis and Muscidifurax raptor. The latter is a 

 small clear-winged species, dark in colour, which was reared in 

 some numbers from the pupa; of various flies in Illinois. The 

 larva of this parasite lives in the puparium and feeds externally 

 on the pupa of the fly, sucking its juices. 



Fig. 31. Pteromalus sp. from pupa of blow-fly. 



NichoUs (191 2, p. 87), working in Saint Lucia, makes the 

 following statement : " There are certain very small parasitic 

 hymenoptera of the family Chalcididce which are probably of 

 some service in keeping down the numbers of some of the flies 

 here considered. These insects deposit their eggs in the body of 

 freshly hatched larvae. This appears to have no effect on the 

 growth or development of the host until it pupates, when the Qgg 

 hatches and the resultant guest larva undergoes its development 

 at the expense of the pupa. In a number of cases the period of 

 time from laying the &%^ to the emergence of the hymenopteron 

 varied from twenty-two to twenty-eight days. On one occasion 



16 — 2 



