2 BULLETIN 1487, U. S. DEPARTMENT OF AGRICULTURE 
cally any life-history study, or in the course of the mere rearing of 
insects for host-and-parasite records. It has been the source of much 
annoyance in rearing work because the exact nature of parasitism 
is sometimes difficult to ascertain, and not infrequently hyperparasites 
have pees mistaken for primaries, with consequent confusion in the 
records. 
An exhaustive study covering the entire field of insect hyperpara- 
sitism would be a tremendous undertaking. For acquaintance with 
this subject we shall probably need to rely upon gradual additions to 
our knowledge supplied by observations made in the course of bio- 
logical studies in connection with a variety of insect problems. In 
this way we shall gradually improve our understanding of a most 
interesting field of insect behavior that has been only superficially 
investigated, but which is intimately related to problems in economic 
entomology. This bulletin is an attempt to review briefly the more 
general features of hyperparasitism, and to present certain data 
upon the habits, biology, and interrelationships of the hyperpara- 
sites affecting Apanteles melanoscelus (Ratzeburg), a valuable pri- 
mary parasite of the gipsy moth. 
EXTENT OF HYPERPARASITISM 
Practically no parasitic species of primary rank escape the attacks 
of hyperparasites. The extent to which particular primary parasites 
are themselves parasitized is in large measure dependent upon the 
habits of those species, particularly upon the degree of their exposure 
or concealment while in the cocoon or puparium and upon the length 
of the period spent in this stage. Some species of primary parasites, 
of which A. melanoscelus is an especially good illustration, remain in 
their exposed cocoons throughout a large part of the period during 
which hyperparasites are active, and are extremely heavily parasitized. ~ 
Certain other primaries spend a long hibernation period as immature 
larvae within the body of the host and, upon completing their devel- 
opment in the spring, form their cocoons or puparia in situations 
quite inaccessible to hyperparasites. A. lacteicolor Viereck, an impor- 
tant parasite of the brown-tail moth larvae, is one of this type (26)’, 
and only a relatively small proportion of its cocoons are attacked. 
Nevertheless a certain degree of hyperparasitism occurs in such cases, 
and even with species whose cocoons or puparia are completely pro- 
tected from attack. Under some conditions, as will be mentioned 
later, it may even become severe. 
Certainly hyperparasites play an important part in the maintenance 
of the balance between insect species in nature, for biological 
relationships between hosts, primary parasites, and hyperparasites 
are very intimate. This is sometimes not so readily appreciated as 
affecting primaries and hyperparasites, because of the complexity of 
their relationships, and because most of the observations regarding 
hyperparasitism have been merely incidental to other studies. 
With some species of primary parasites the prevention of exces- 
sive increase is not so obviously the work of hyperparasites. In 
the case of Apanteles lacteicolor, previously mentioned, the failure 
to find a sufficient number of suitable summer hosts to carry the 
2 Reference is made by number (italic) to ‘‘Literature cited,’’ p. 34. 
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