884 MAUD D. TfAVILAND 



These terms may be illustrated with examples from the 

 aphid complex as follows : 



Parasitism a]ih id + A ] ) li i d i u s 



Epiparasitisni aj)hid+ Aphid in .s+ I Lygoceru.s and 



y x\ H a p n G s 



Metaparasitism aphid + A p h i d i u s + A s a j) h e s + L y g o e c r u s 



C A s a p h e s or 

 Hypeqjarasitism aphid+Aphidius+ J Lygocerus or 



( Charips 



The possibility of ' hyper-hyperparasites ' has been suggested 

 by some writers, but although obligative hyperparasitism of 

 the second degree may occur, I am not aware that it has been 

 definitely proved. The records that seem to point to it are 

 probably due to epiparasitism among hyperparasites. 



Apart from their economic importance, cases such as those 

 described are of much Inological interest, as throwing light on 

 the origin of parasitism in the Hymenoptera parasitica. 



Thus the epiparasitism of Lygocerus and Asaphes 

 may exceptionally become metaparasitism, if, by chance, one 

 species oviposits directly upon the larva of the other ; and 

 a stage further has been reached in Coccophagus and 

 Theronia which are as often hyperparasites as parasites. 

 Fiske says of the latter (3) that it is so frequently a ' super- 

 parasite ' that it is in danger of becoming a hyperparasite. 

 From such forms as these it is not a great step to the obligative 

 hyperparasitism of, for example, Charips. 



Epiparasitism is brought about by a high proportion of 

 parasites to the host population. Fiske (3) has made an 

 ingenious calculation, showing that as the incidence of para- 

 sitism rises, the chances of epiparasitism rise likewise. Thus, 

 given a hundred hosts, by the time that the parasite has laid 

 ten eggs, there is an even chance that one will have been placed 

 in a host already infected, and so on, mitil with fifty eggs the 

 odds are even that no less than ten ovipositions ^^•ill have been 

 duplicated in this way. But although hyperparasitism may 

 have arisen from epiparasitism, through metaparasitism, 

 primary parasitism cannot be accounted for thus. 



