6 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 47 



thread and with bits of foliage taken from the host plant. Hence, 

 bags on maples look different from those on arborvitae. 



Each bag is enlarged to accommodate the lapidly growing 

 larva inside and is carried everywhere the larva goes. The larva 

 sticks its head out of the bag to feed, but quickly retreats when 

 disturbed by birds or other enemies. By late summer, when the 

 bag is 1Y2 to 2 inches long, the larva matures, pupates, and 

 transforms to the adult stage. The adult male, a black, fuzzy 

 moth, emerges from its bag and flies about to mate with the 

 wingless female, which remains in the bag while she lays 500 

 or more eggs. After egg-laying, the female dies. The bagworm 

 produces only one generation a year in Illinois. 



Because only the male adult flies, infestations of bagworms 

 are spread principally in the larval and egg stages. Small larvae 

 suspended by their silken threads may be carried by the wind 

 for considerable distances. Larger larvae often crawl from one 

 plant to another in search of food. Larvae or bags containing 

 eggs may be inadvertently transported by human beings. 



Control Measure 1, 3, 11, or 21 (end of circular) as soon as 

 the eggs hatch. Sprays applied in late summer after the larvae 

 stop feeding, or during the winter, are ineffective. The infestation 

 can be reduced by picking and burning the overwintering bags. 



Arborvitae Leaf Miner, Argyresthia thuiella (Pack.). — 

 Feeding by the leaf -mining caterpillar of this species on the in- 

 sides of needles causes the tips of arborvitae branches to turn 

 whitish, tan, and brown. Less than one-fourth inch long, each 

 greenish, red-tinged caterpillar comes from one of several eggs 

 deposited on the leaves by a small moth in the spring. This pest 

 may produce more than one generation in a season, and consid- 

 erable damage may result from its feeding. 



Control Measure 2 (end of circular) when moths are flying. 

 The use of DDT may result in a build-up of mites. 



Spruce Spider Mite. — See under Spruce. Control Measure 9 

 (end of circular). 



Juniper Scale, fig. 28. — See under Juniper. Control Measure 

 3 (end of circular). 



ASH 



Red-Headed Ash Borer, Neoclytus acuminatus (F.), fig. 3. — 

 The short, white, round-headed grub of this species may girdle 



