482 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



of Figitidse also have this habit, ovipositing into aphids in order to 

 breed upon the aphidiines infesting them. Considered from an eco- 

 nomic standpoint, these indirect parasites are of no greater importance, 

 are capable of no greater harm, than are the other hyperparasites. In 

 fact they are less to be feared as a general rule since their life-histories 

 are more complex and the more complex an insect's life-history is, 

 other things being equal, the less possibility there is of its becoming 

 abundant. 



Secondary Parasitism 



The type of host-relationship most closely allied to indirect para- 

 sitism, and most generally confused with it, is secondary parasitism. 

 While these two forms of symbiosis bring about the same final result, 

 i. e., the destruction of the primary parasite, the manner of accomplish- 

 ing this end is very different. Strictly speaking, a secondary parasite 

 is merely a primary parasite of a primary parasite. While this is also 

 true of the indirect parasite, they differ in that the adult of the indirect 

 parasite does not oviposit directly in or upon its host, but into or upon 

 the host of the primary.^ The adult of the secondary parasite de- 

 posits its eggs directly into or upon the body of the young primary. 

 The life-history of the true secondary is very simple as compared to the 

 complex life-history of the indirect parasite. In the one case two 

 insects only, the secondary and its host the primary, are concerned. 

 In the other three insects, the indirect parasite, the primary parasite 

 and the host of the primary are all directly concerned. 



True secondary parasitism is of very common occurrence in nature, 

 and is of great importance in the natural control of insects. Practically 

 all species of primary hymenopterous parasites, and especially the 

 cocoon-forming groups of which the Ichneumonoidea compose the 

 majority, are greatly subject to attack by these insects. The Tach-, 

 inidse and other parasitic Diptera are also destroyed in large numbers. 

 True secondary parasitism is of most common occurrence among the 

 Chalcidoidea and is found especially in the families Eulophidae and 

 Pteromalidae. It also occurs in the Eurytomidse, Elasmidse, Cal- 

 limomidse and Chalcididae. It occurs very uncommonly, if at all, in 

 the Encyrtidse, since in that highly specialized family indirect para- 

 sitism takes the place of secondary parasitism. I do not call to mind 

 at this time any case of secondary parasitism, as here defined, in the 

 Proctotrypoidea or Cynipoidea, although in the latter indirect para- 

 sitism occasionally occurs. Secondary parasitism should occur in 

 both of these superfamilies, however, since many species are parasites 

 of Diptera and they will undoubtedly be found to attack some of the 



1 In the case of Perilamyus hyalinus, the oviposition habits are unknown, but the 

 young parasite larva or ■planidium is first found on the outside of the caterpillar. 



