484 journal of economic entomology [vol. 9 



Tertiary and Quaternary Parasitism 



Parasitism of a stage beyond that of secondary — if we disregard 

 those cases of accidental or chance parasitism — is of not at all common 

 occurrence. I do not at this moment recall a single authentic case of 

 true quarternary parasitism, although such have been recorded. It 

 will generally be found in the instances where parasites are recorded 

 as quaternary that they are only accidentally so, the same species 

 being by nature either secondary or tertiary. Some parasites such as 

 Dibrachys boucheanus are so omnivorous in their food habits that they 

 will develop on practically any parasite larvae enclosed in a cocoon or 

 puparium. This being the case, if they oviposit into a cocoon con- 

 taining larvse of a tertiary parasite they are able to develop on the ter- 

 tiary larvae and then they become numerically speaking quaternary 

 parasites. They are not, however, obligatory in this role, and if thej'' 

 are to be designated as quaternary at all the term should be modified 

 by the word accidental. There are grave doubts as to whether an 

 obligatory quaternary parasitic insect exists. 



Obligatory tertiary parasitism does exist in nature and will no doubt 

 be found to be a fairly common phenomenon when the life-histories of 

 more parasitic insects are thoroughly known. The best instance of 

 true tertiary parasitism is that of the Eulophid, Asecodes albitarsis. 

 The writer has made hundreds of dissections of cocoons of various 

 microgasterine parasites in New England and in every case Asecodes 

 was found to be a true tertiary parasite, breeding generally upon 

 Dibrachys boucheanus, a true secondary. Other species of the Ente- 

 donini will without doubt be found to belong to this categor5^ 



Dr. L. O. Howard in his interesting paper on the parasites of the Tus- 

 sock moth, at the close of his chapter on the interrelations of the para- 

 sites, says: "We would naturally have expected a period of abundance 

 of tertiary parasites to have followed that of the secondary parasites. 

 This, however, was not the case. Tertiary parasitism seemed to be 

 comparatively rare and was only definitely proven in the case of As- 

 ecodes albitarsis and Dibrachys boucheanus, the latter being usually a 

 secondary parasite. . . . There must be a limit to this work of 

 parasite upon parasite at some point and it seems certain that tertiarj'' 

 parasitism is rare and that quaternary parasitism seldom occurs." 



As mentioned above, Dibrachys is in reality a secondary and be- 

 comes tertiary in this case only through accident and its omnivorous 

 food habit. Asecodes is, however, an obligatory tertiary parasite. 

 I would define then as tertiary parasitism that type of symbiosis 

 where a parasite is obligatory upon an obligatory secondary. A true 

 quaternary would necessarily be obligatory upon an obligatory ter- 

 tiary parasite. I believe with Dr. Howard that there must be a limit 



