328 PARASITISM 



individual host super- or multiparasitic relations are involved. 

 An example of this kind is instanced by Haviland (1922a) with 

 respect to hyperparasites of aphides through the Braconid 

 Aphidius. The Aphidius may be attacked by the endoparasitic 

 Cynipid Charips or by the ectoparasites Lygocerus (Proctotry- 

 poidea), Asaphes or Pachycrepis, the two latter being Chalcids. 

 The Charips, along with its Aphidius host, perishes as the result of 

 attack by one or other of these ectoparasites. The latter, on 

 their part, frequently suffer from mutual competition. Thus, 

 Haviland states that when two of these hyperparasites occur 

 together, and they may belong to the same or to different species, 

 only one survives or both may perish consequent upon the 

 exhaustion of the nutritive supply. 



Hyperparasites in general are far less restricted in their host- 

 selection than most Hymenopterous primary parasites. They 

 are able to adapt themselves to a wider range of hosts, especially 

 in the absence of preferred species — a trait which explains the 

 heavy attacks certain introduced primary parasites undergo in 

 countries where the normal and regular hyperparasites are absent. 

 The Chalcid Dibrachys cavus (houcheanus Ratz.), for example, will 

 attack an immense range of hosts, including many Lepidoptera and 

 Diptera and several Coleoptera ; as a rule it behaves as a hyper- 

 parasite, but in other instances it is a primary parasite, 

 especially of the larvae of Microlepidoptera. In many cases, when 

 Hymenopterous parasites exercise a wide and apparently indis- 

 criminate range of host-selection, they will prove to be secondary 

 rather than primary parasites. 



The vast majority of hyperparasites live externally to their 

 immediate hosts, which are either concealed within the original 

 host or enclosed in puparia or cocoons. The internal feeding 

 habit is consequently rare ; it obtains in Charips, already 

 mentioned, and also as a special adaptation in certain other 

 instances. 



Parasites of a tertiary order are often referred to in literature, 

 but proof that this type of parasitism is a constant and obligatory 

 feature of the species concerned, and not merely a phase of 

 multiparasitism, is in many cases non-existent. As an example 



