2 BULLETIN" 295, U. S. DEPARTMENT OF AGEICULTUEE. 



the development of forest trees, with a view of discovering possible 



methods of elimination or at least amelioration of its ravages. 



Definite details were gathered only in certain areas within the 



States of Montana and Idaho, but correspondence with the other forest 



insect field stations in the West, together with larvae collected and 



forwarded from those stations, proves that this moth occurs almost 



everywhere in the West. Considering that Packard records its 



occurrences in New York and Pennsylvania, it is evident that this 



insect is probably distributed over most of the United States. Its 



habits and the result of its larval work also apparently do not vary 



materially anywhere in its range. These facts lead to the conclusion 



that the remedy outlined below should be as effective in other regions 



as in the West. 



DESCRIPTION OF THE INSECT. 



THE ADULT. 



The length of the moth (PI. II, fig. 1) is about. one-half inch. There 

 is no appreciable difference in size and coloration between the two 

 sexes although the general color of individual specimens varies from 

 a light gray to a reddish gray and the body of specimens having 

 the latter hue on head and thorax is usually dark gray. The under- 

 side of the entire insect is of a uniform gray color. 



The wing expanse is from 1|- to 1^ inches. The fore wings are shaded 

 reddish on the basal and terminal fields, the median space, divided 

 from the latter by W-shaped lines, being blackish and gray, these two 

 colors being again divided by a small white bar on a brownish field. 



The hind wings are pale yellowish white, the color becoming deeper 

 toward the terminal fringe, which is paler than that of the fore wings, 

 on which it frequently shades to a dark gray. These characters 

 agree fairly well with Grote's description. 



THE LARVA. 



When full grown the caterpillar (PI. II, fig. 2) is about three-fourths 

 of an inch in length. The head is chestnut brown, the mandibles black. 

 The body is naked, with a series of dots, darker than the skin, from 

 each of which issues a single bristle. It has three pairs of thoracic 

 legs, four pairs of abdominal prolegs, and a pair of anal claspers. 

 The body varies greatly in color, which ranges from a dirty white, 

 through reddish yellow, to a vivid green. The larva found in yellow 

 pine is almost invariably gray-brown , resembling the color of the 

 hark of the host tree, while those in Douglas fir are of such a vivid 

 green color that it seems almost incredible that they should be repre- 

 sentatives of the same species which infests pine. Rearing them to 

 the adult stage, however, always dispels any doubt in this regard. 



Variations in color, about which Grote and Kellicott differ, are 

 evidently merely a matter of host differences. 



