INSECT ENEMIES OF EASTERN FORESTS 347 
cremaster, which is often provided with hooks to hold the pupal shell 
in place while the adult emerges from it. A softening fluid from the 
emerging insect also aids in its escape from the cocoon. 
FEEDING HABITS OF LEPIDOPTERA AND CHARACTER OF INJURY 
Brief reference has already been made to the characteristic feeding 
habits of the larvae. Fortunately most of our native species are held 
down more or less by the natural control factors, so that the feeding 
they do seldom attracts attention. The control of those species that 
increase enough to cause serious injury is one of the big problems 
of the forest entomologist, the forester, and others responsible for 
the care of trees and shrubs. Knowledge of the biology of the insect 
concerned and the character of its work is necessary before one can 
decide intelligently if and when control measures are advisable or 
practical. 
The external structure of the larva, its habits, the food plant, and 
the character of its work can be used in the identification of the pest. 
Although many species are borers of buds, stems, twigs, bark, or wood, 
most of them are leaf eaters, or defoliators. The latter group may 
mine, skeletonize, or completely devour the leaves, and when the larvae 
are abundant their feeding may completely defoliate the food plant. 
It is therefore important to point out some of the characteristics of 
these insects and to give the common names used in identifying various 
species or groups. 
The leaf miners are found among the beetles (Coleoptera), true 
flies (Diptera), and sawflies (Hymenoptera), but by far the greatest 
number of species having this habit is found among the Lepidoptera, 
and here are also found the best developed leaf-mining habits. One . 
or more species of these tiniest of moths may be found inhabiting the 
foliage of practically every species of plant. All have at least one 
generation annually, but some species have several. The mines, in 
general, are of two principal kinds—linear and blotch. The linear 
mines may take a straight or serpentine course and the blotch mines 
may be circular, oblong, or of other shapes. There are many inter- 
gradations between the two types. 
Some species of leaf miners are sap feeders, removing very little 
of the parenchyma; some are adapted for sap feeding in the early in- 
stars but when partly grown acquire tissue-feeding mouth parts; and 
others are entirely tissue feeders. The mining habits differ, depending 
on the extent of the life cycle spent in the mines. The larvae of Para- 
clemensia acerifoliella (Fitch) (family Incurvaridae) are leaf 
miners only during their early larval life, later becoming leaf cutters 
and casebearers. The larvae of Bucculatrix (family Lyonetiidae) 
vacate the mine when young and feed openly, skeletonizing the foliage, 
and are commonly considered skeletonizers. Those of the Nepticulidae 
and some species of other families vacate the mines only when they 
are full grown. The larvae of Coleophoridae, commonly called case- 
bearers, mine portions of the food plant and from the material they 
construct portable cases which they carry around on the body, and 
enlarge as they grow. 
In the Gracilariidae, the largest family of leaf miners, the larvae 
of species in the genus @racilaria become external, but concealed, 
feeders when’ partly grown. They spin silken threads across the 
