312 ENTOMOLOGY 
Hyperparasitism.—Not only are primary parasites fre- 
quently attacked by other, or secondary, parasites, but tertiary 
parasitism 1s known to occur in a few instances, and there is 
some reason to believe that even the quaternary type exists 
among insects, as in the following case. 
The caterpillar of Hemerocampa (Orgyia) leucostigma 
defoliates shade trees in the northeastern United States. An 
enormous increase of this species in the city of Washington in 
1895 was attended by a corresponding increase of parasitic 
and predaceous species, and this unusual opportunity for the 
study of parasitism was made the most of by Dr. Howard, 
from whose admirable paper these facts are taken. 
The primary parasites of 7. leucostigma numbered 23 spe- 
cies—17 Hymenoptera and 6 Diptera; of the hyperparasites 
(all hymenopterous) 13 were secondary, 2 and probably 5 
were tertiary, and one of these (Asecodes albitarsis) may un- 
der certain conditions prove to be a quaternary parasite. To 
illustrate—The ichneumon Pimpla inguisitor, an important 
primary parasite of lepidopterous larvee, lays its eggs in cater- 
pillars of Hl. leucostigma; its larve suck the blood of their 
host and at length spin their cocoons within the loose cocoon 
of the Hemerocampa. These cocoons have yielded a well- 
known secondary parasite, the chaleid Dibrachys boucheanus. 
Now another chaleid, Asccodes albitarsis, has been seen to issue 
from a pupa of this Dibrachys, thus establishing tertiary para- 
sitism. Furthermore, it is quite possible that Dibrachys itself 
is a tertiary parasite, in which event the Asecodes might be- 
come a parasite of the quaternary order. 
Economic Importance of Parasitism.—If a primary para- 
site is beneficial, its own parasites are indirectly injurious, gen- 
erally speaking; while those of the third and the fourth order 
are respectively beneficial and injurious. The last two kinds 
are so rare, however, as to be of no practical importance from 
an economic standpoint. The first two kinds are of immense 
economic importance, particularly the primary parasites. 
“Outbreaks of injurious insects,” says Howard, “are fre- 
