INSECT ENEMIES OF EASTERN FORESTS 17 
Most of the parasites belong to a few families of wasps (Hymen- 
optera) and flies (Diptera). The parasitic wasps oviposit on, in, 
or near the host, and the parasite larvae feed either externally or in- 
ternally until they reach maturity. Parasitic wasps may develop’ 
singly or gregariously, and in the case of those that develop poly- 
embry onically as many as 100 or more individuals may be produced 
from a single egg. The parasitic flies either oviposit or larviposit on, 
In, or near the host, although there are some species that deposit their 
eggs on the foliage and these eges must be devoured by the host insect 
to be effective. The larvae of parasitic flies, called maggots, usually 
develop within the body of the host, whereas the larvae of parasitic 
wasps may be either internal or external feeders. After the wasp 
larva or fly maggot becomes full grown the host usually dies. The 
parasite then pupates in a cocoon, or puparium, or as a naked pupa 
either within the remains of the host, or without, if the larva is an 
external feeder or if it leaves the host before it pupates. 
Most native forest insects, with the exception of borers and some 
forms that feed imside the host plant, are attacked by an abundance 
of parasites which often include a great many species. AI] stages 
of the host from egg to adult may be attacked, although, generally 
speaking, the larvae and pupae are most heavily parasitized, Para- 
sites range in size from minute forms that attack insect eggs to some 
with ovipositors several inches long, which parasitize wood borers in 
their tunnels. 
Unfortunately many of the parasites that attack forest insects are 
themselves preyed upon by other parasites, called hyperparasites. 
Hyperparasitism may be occasionally carried to the second or third 
degree, thus making the host-parasite relationship quite complex. 
Some of the more important predaceous enemies of forest insects 
are beetles belonging to the families Cleridae, Ostomatidae, Carabidae, 
and Coccinellidae, lacewing flies of the family Chrysopidae, several 
families of true bugs of the order Hemiptera, and the dipterous family 
Syrphidae. Often both the immature and adult forms of predaceous 
insects feed directly upon all stages of their hosts. Ants of several 
species are voracious feeders, often devouring not only large numbers 
of defoliating larvae as they come to the eround to pupate, but also 
pupae in the “duff, and newly emerged adults. They likewise destroy 
the broods of borers and bark beetles exposed during peeling opera- 
tions on control projects. 
The effectiveness of parasites and predators is very difficult to meas- 
ure accurately, but it is safe to say that these natural enemies play a 
very important role in keeping forest insects in check. Their effec- 
tiveness is dependent on many factors, such as the character and habits 
of the host insect, density of population of the host, presence of al- 
ternate hosts, degree of hyperparasitism, conditions affecting hiber- 
nation, and artificial control measures. 
The larvae of some of the roundheaded borers are voracious feeders 
and are often indirectly beneficial in that they devour the inner bark 
so rapidly that they rob the more primary bark beetles infesting the 
same tree of their food. This is a case of competition between two 
species of insects, one of which is capable of killing trees, the harmless 
species putting the destructive one to a disadvantage. Such larvae 
are often referred to as robbers. 
