210 OHIO EXPERIMENT STATION: BULLETIN 332 



hazel*, beech, ironwood, hazelnut and sour wood. Those marked 

 with an asterisk are most severely attacked under Ohio conditions. 



Distribution. — Geographically, the insect occurs over the entire 

 section of the United States east of and including the states of the 

 Mississippi Valley, and as far north as Nova Scotia. Ecologically, 

 it is found more as a city pest than of the rural districts ; hence we 

 have come to think of it as specially inimical to the trees of densely- 

 populated areas. In recent years, however, considerable injury has 

 been done by way of defoliating apple trees on farms, and during the 

 last two seasons rather extensive injury has been done in woodlands 

 in southern Ohio. 



Natural enemies. — The white-marked tussock moth is heavily 

 beset by natural enemies; otherwise its depredations would be 

 unbounded. For a few years it will be observed as gradually in- 

 creasing in numbers until it becomes a veritable scourge; then it 

 will be noted in the descendency, sometimes gradual and sometimes 

 sudden. Following a severe outbreak, communities usually enjoy 

 a few seasons of comparative freedom. The explanation of this 

 procedure is that when the insect begins to increase in numbers its 

 parasites also increase but for a time may not keep apace. At 

 last they overcome the pest and thus veritably eat themselves out of 

 house and home, whereupon they perish. No periodical regularity 

 exists because associated factors are variable. The weather, for 

 instance, has much to do with the development of host and parasite. 

 Conditions which may be favorable to the one may not be so for 

 the other. 



Insectivorous birds in the rural districts constitute an impor- 

 tant factor in its suppression. E. H. Forbush, ornithologist to the 

 Massachussetts Board of Agriculture, lists forty-seven species of 

 birds as feeding on hairy caterpillars and states that probably all 

 these feed upon this pest. In the urban districts birds do not 

 abound and therefore are not such a potent factor in its suppression. 



Luckily the insect enemies of the white-marked tussock moth 

 do not shy at man and his ways and are ,therefore, invaluable allies 

 to him in checking the ravages of the pest in cities. As a result of 

 the careful work of Dr. L. 0. Howard (6), twenty-one primary para- 

 sites were recorded, and to these H. C. Yingling (7) has added two 

 others, Ichneumon unifasciatorius Say and Ichneumon seminiger 

 Cresson. Of the parasites listed, seventeen are Hymenoptera and 

 six are Diptera. Hyperparasites totaling fourteen were listed by 

 Doctor Howard. These included secondary, tertiary and possibly 

 quarternary parasites. The primary parasites are of course the 



