REVISION OF STREPSIPTERA PIERCE. 27 



live many days after the exit of the male are now disproven by the 

 hibernation records on Polistes annularis. 



2. In most cases the largest percentage of parasitized hosts are 

 females. Only a small percentage of the males of any species have 

 been found parasitized. Parasitism of females sometimes becomes 

 very high — 53.1 per cent. The highest percentage of parasitism 

 recorded is 90 per cent for Andrena lapponica. Next to this must 

 come Andrena craufordi. Of 145 bees taken between April 2G, 1906, 

 and May 2, 1906, 81, or 55 per cent, were parasitized, and of the 

 65 females, 57, or 87 per cent, were parasitized, while onl}' 24, or 

 30 per cent of the 80 males were affected. The percentage in Andrena 

 lapponica for 1887 is also worthy of note — 52.7 per cent of 180 bees. 



3. In the majority of cases there are a great many more male 

 than female parasites. The only two exceptions — A. pratensis and 

 A. tibialis — were winter and early spring records. 



4. Male parasites were found in all parts of the hosts' abdomen 

 except the ultimate or genital segments. Female parasites seldom 

 occur before the fourth segment, although they are sometimes 

 found in the third. The third segment is the normal location of 

 the males, and the fifth the normal location of the females. A 

 parasite will find exit any place around the periphery of a segment 

 where it can get sufficient room. According to Perkins (1905) this 

 does not hold in the case of Homopterous hosts. 



5. Both sexes of parasites are often found together in the same 

 individual. 



6. A host will nourish as many parasites as can find room in its 

 body. The largest number of larval parasites found in a host is 31, 

 while the largest number of male pupae found exserted from the 

 body of a host is 15. The host in this case (P. annularis) lived 

 several days; it was taken with the nest or may have hatched after 

 the nest was captured. Mr. Bowditch took a male P. paUipes in 

 the field, bearing 10 male pupa?, and Mr. Dury took a female bearing 

 9 pupa?, which was so feeble that it could hardly move around. 

 The latter also took a wasp in the field from which 5 males had 

 emerged. 



2. EFFECTS OF PARASITISM ON THE HOST. 



1. Extermination of race or species. 



Although the parasite lives within the body of the host without actu- 

 ally destiwing any of its organs, the latter is extremely disabled by the 

 extraction of its body juices through the absorptive power of the para- 

 site. The result is that the host dies without being able to reproduce. 

 When conditions are such that the parasites can not readily be 

 transferred from race to race of hosts, or are by conditions con- 

 centrated against the individuals or colonies in a limited locality 



