90 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



The females lay eggs in groups of 2 to 40 on the under side of 

 oak leaves, on tree trunks, or other convenient places. The young 

 caterpillars skeletonize the leaves, and later, as they reach full 

 growth, consume all the leaf. Two generations are produced each 

 year. The moths fly in June and again in November. The winter is 

 passed in the egg and early larval stages. 



Natural enemies include the spined soldier bug, a tachinid fly, 

 and several species of wasplike parasites. A wilt disease takes a 

 heavy toll of the caterpillars during epidemics. As a result of these 

 natural control agencies, outbreaks occur only at irregular in- 

 tervals. 



This defoliator can be controlled by spraying in March and 

 April with lead arsenate or DDT emulsion sprays when the worms 

 are very small and again during the latter part of July and early 

 in August. 



TUSSOCK MOTHS 



The tussock moths (Lymantriidae) , a very destructive group 

 of leaf-feeding insects, attack coniferous as well as broadleaved 

 trees. The adults are dark-brown or dull-colored, very fuzzy moths, 

 chiefly nocturnal in habit. The males fly, but the wings of the fe- 

 males are but short pads, of no use for flight. The abdomens of 

 the females are large and covered with a mat of dark-gray hair. 

 The full-grown caterpillars are strikingly marked and very hairy 

 with prominent pencils or small tufts of hairs on all the body seg- 

 ments, the whole giving much the appearance of a toothbrush. The 

 larval hairs are easily detached and in some species are somewhat 

 poisonous, causing a rash or eczema when they come in contact 

 with the skin. 



The female lays small white eggs in a mass on top of her own 

 cocoon and covers them with a frothy, gelatinous secretion in 

 which are embedded hairs from her body. The eggs hatch into 

 tiny, very hairy caterpillars. Since the females are unable to fly, 

 the principal time of dispersion is probably during this young 

 caterpillar stage, for the light, hairy caterpillars can be easily 

 picked up and carried by air currents for long distances. When 

 disturbed or when in search of food, the larger larvae lower them- 

 selves to the ground by silken threads and travel rapidly, but dis- 

 persion at this stage could be for only short distances. Pupation 

 takes place within a gray cocoon made of silk mixed with larval 

 hairs. The cocoons may be attached to the twigs, limbs, or trunks 

 of trees or on the underbrush. They are sometimes formed in 

 masses six or seven layers deep, and in such masses the moths 

 from the lower layers are unable to emerge. 



The Douglas-fir tussock moth (Hemerocampa pseudotsugata 

 McD.) (3) (fig. 36) is a defoliator of major importance in the 

 Douglas-fir and true-fir forests of eastern Oregon, Washington, 

 British Columbia, Idaho, Colorado, and Nevada. It was first dis- 

 covered in 1918 in British Columbia, where it was severely de- 

 foliating Douglas-fir, and later was noted at several points in 

 Canada. It was first found in the United States in 1927, defoliating 

 alpine fir at Jarbridge, Nev. From 1927 to 1930 a major outbreak 



