THE TWO-LINED CHESTNUT BORER 275 



protection; they appear to withdraw it at will. The pupal period 

 is passed in the partly cast larval skin. Fifteen days are required 

 for development of the larva and pupa. There are several genera- 

 tions each season. The greatest damage is caused by the beetles 

 on the young leaves and small tender shoots. 



Control. Spraying with arsenicals has proved effective. The 

 worst injury occurs in nurseries, and these remedial measures are 

 for use there. 



The Locust Borer (Cyllene robinice Forst.). This beautiful 

 beetle, black, with gold markings, nearly three-fourths of an inch 

 long, is a common pest of locust trees in some sections. Branches, 

 and sometimes an entire tree, succumb to its attack (Fig. 280). 

 In the fall it occurs on flowers of the goldenrod. 



i 



FIG. 278. Mottled willow borer. FIG. 279. Cottonwood leaf beetle, enlarged 



and natural size. (Ruggles.) 



The whitish eggs are laid in crevices in the bark in September. 



Control. Some repellent wash, containing arsenate of lead 

 and applied very early in the fall, is recommended. Fish -oil soap, 

 with the addition of crude carbolic acid and arsenate of lead, at 

 the rate of six pounds of the latter for every fifty gallons of the 

 wash, is suggested. Badly infested trees should be cut down and 

 burned during the winter or early spring. 



The Two-lined Chestnut Borer. In some oak-growing regions, 

 Minnesota for example, this is a very destructive insect (Agrilus 

 bilineatus Oliv.). It kills more oaks than any other species of 

 insect so far discovered. The grubs make burrows beneath the 

 bark in the growing layer. The : r tunnels cut off the food supply 



