INSECT PESTS OF OHIO SHADE AND FOREST TREES 217 



fly about seeking the females. The latter do not leave the bags at 

 this time but merely protrude their bodies sufficiently to permit 

 copulation, withdraw into the bags and deposit their eggs within 

 the shelter of the cast pupal skin inside. Later the spent female 

 wriggles out of the bag and falls to the ground. The eggs con- 

 stitute the over- wintering stage, and it will thus be seen that 

 there is but one annual brood of the insect. (See Plate XXII, for 

 detailed illustrations of the hfe history.) 



Nature of injury. — Two types of injury are effected by this 

 insect. The first and by far the less important is that of occas- 

 sionally causing the death of twigs by strangulation. When the 

 larva hangs up its bag for the winter, occasionally enough silk of 

 such a tough, lasting nature is banded about the twig that sap flow 

 is cut off the following year, and the twig dies. 



The principal harm done, however, is the destruction of the 

 foliage by the feeding caterpillars. Occasionally complete defolia- 

 tion occurs and this, particularly in the case of conifers, may cause 

 the death of the host. (See Plate XXIII.) 



Food plants. — Doctor Felt records a list of twenty-thiee food 

 plants, which includes our more common trees. Hard maple, syca- 

 more, horse chestnut, arbor vitae, cedar, sweet gum, black locust and 

 willow suffer more severely under Ohio conditions than other hosts. 



Distribution. — The range of greatest destructiveness in Ohio 

 extends over the southern part of the State and in greatest inten- 

 sity in the southwestern and southeastern sections. Occasionally 

 considerable harm is noted as far north as Columbus, but rarely 

 is the insect observed north of a line drawn east and west through 

 the northern part of Franklin County. 



Natural enemies. — On account of the tough protecting bag by 

 which the insect is sheltered throughout almost its entire life cycle, 

 birds do not constitute an important factor in its suppression. Even 

 the cocoon-piercing woodpeckers find little inducement to attack the 

 bags during the winter because the eggs within evidently do not 

 prove such an attraction as the juicy pupae of other species. For- 

 tunately, however, parasitic insects are not excluded by the bag and 

 several are known to be of great usefulness in subduing the pest. 

 The consensus of opinion of several writers is that the three most 

 common are Pimpla inquisitor Say, P. conquisitor and Allocota 

 thyridopterigis Riley. These insects invade the bag and their 

 larvae develop on the body of the bag worm within, and later pupa- 

 tion occurs within the shelter of the bag. Beyond question these 

 insects are largely responsible for the natural decline of bag-worm 



