REVISION OF STEEPSIPTERA — PIERCE. 15 



RELATIONS TO HOST. 



The subject which deals with the relationships of these parasites 

 to their hosts is many sided and complicated, but it certainly contains 

 many points of great interest to the student of parasitism. A 

 division, therefore, into the main groups of relationships will probably 

 make the discussion more coherent. These divisions are : 



1. The actual relationships of the host to the parasite. 



2. The effects of parasitism upon the individual hosts. 



3. The effects of various host conditions upon the parasites. 



4. Seasonal conditions and the biology of the hosts as influencing 

 the biology of the parasites. 



1. ACTUAL RELATIONSHIP TO THE HOST. 



When the young triungulinids leave the body of the parent they 

 find themselves crawling over the body of the parent's host. They are 

 restless for they must reach some new host. The insect, then, which 

 now bears them, and which for convenience will be known hereafter 

 as the maternal host, becomes the first agency of transfer of the 

 minute triungulinids. There are obviously several ways in winch 

 the parasites may reach new hosts, and probably all are followed in 

 actual life. 



They may be carried direct to the nest of the maternal host, where 

 they may find new hosts immediately. This is especially possible in 

 the case of colonial insects, for there the parasites may pass from one 

 cell to another until a proper host is found. But if the maternal host 

 is a male solitary insect, or if the hosts are not nest builders (in the 

 case of Orthoptera, Homoptera, Heteroptera) then this is not the 

 method of transfer. 



It is, however, almost out of the question that the host should carry 

 the triungulinids to its own young, because the observation of Perez 

 that there is a loss of function in parasitized females would indicate 

 that there is no nest building by affected individuals. Perez (1886) 

 looks at the matter in this light: "Ildevrait par consequent exister 

 dans chaque espece d'abeilles nourissant ces parasites, une lignee, 

 une race exclusivement affectee, a leur entretien, ce que, a priori, est 

 absolument improbable." 



They may leave the maternal host at some place frequented by 

 other individuals of the same species. In case of bees this will be a 

 flower of a certain species, which flower or rather plant may be 

 known as the host plant. The opportunities of reaching a new host 

 are many. Among bees all individuals mature during more or less 

 definite periods and frequent a limited number of flower species, 

 although the males may visit several species of flowers not visited by 

 the females. The little triungulinids may be picked up in a mass of 

 pollen, or they may reach this new host, which must be known as a 



