INSECT ENEMIES OF EASTERN FORESTS 593 
larger than the remainder. These insects are often regarded as a 
single family, but Ashmead (6) defined two, the members of which 
exhibit different habits. 
Famity FIGITIDAE 
Most of the members of the family Figitidae are parasites of dip- 
terous larvae. A few are known to attack aphids, coccids, or hemer- 
obuds, whereas others have been recorded from coleopterous larvae. 
Famity CYNIPIDAE 
The family Cynipidae includes not only true gall makers, but also 
inquilines and a small number of parasites. Most of its members be- 
long to the subfamily Cynipinae, or gallflies, and most of the species 
produce plant galls, within which their larval development is com- 
pleted. 
SUBFAMILY CYNIPINAE 
Although the Cynipinae are known as the gallflies, galls are also 
produced by many other groups of insects. Galls formed by flies, 
moths, beetles, and other insects have been described, but most of 
them are formed by gall midges, mites, plant lice, and true gallflies 
(Cynipinae). The galls made by mites and plant lice have open 
mouths from which the young escape, but the gallflies form a closed 
gall and the insect must make a hole in order to emerge. The forms 
of galls produced by different species of cynipids differ greatly, and 
all parts of the plant, from the roots to the flowers, may be affected. 
In every case the female insect lays an egg in the tissues of the grow- 
ing plant, where development takes place. The larvae are conse- 
quently internal feeders and maggotlike in form. Pupation takes 
place within the larval cell. 
Naturalists have speculated much regarding the phenomenon of 
gall formation, but the problem appears to be still far from being 
solved. There appears to be no evidence that cynipid galls are caused 
by an irritation of the tissues produced by the insertion of the ovi- 
positor or by the injection of fluids at the time of oviposition, although 
certain sawfly galls are caused as a result of the latter. About all 
that can be said is that the cynipid galls are produced as a result of 
reactions of the cambium and other meristematic tissues of the plant 
to the stimulus produced by the living larva. Their formation and 
structure have been studied by Cook (205), Cosens (106), Felt (251, 
153), and others. 
In many species of gallflies there is a remarkable alternation of 
morphologically and physiologically different generations. The galls 
of two successive generations, produced on different parts of the plant, 
often present entirely different forms; and the insects of the two gen- 
erations are so different that they have been described as distinct 
species until, by careful studies of the life cycle, one has been found 
to be the offspring of the other. In species having an alternation 
of generations, one generation consists only of agamic females, where- 
as the other consists of both males and females, which reproduce sexu- 
ally. The latter is the summer stage, whereas the agamic generation 
overwinters. In many species males have never been seen, therefore 
the successive generations are all similar and agamice. 
