274 INSECTS AFFECTING SHADE TREES 



easily controlled by arsenical sprays. Of these, the safest is 

 arsenate of lead. 



The Yellow-spotted Willow Slug. This saw-fly larva is black 

 or greenish black in color. It is a little more than one-half inch 

 long, with heart-shaped, yellowish spots on each side of the body. 

 The adult insect (Nematus ventralis Say) is brownish black 

 marked with yellowish white. It is about one-third of an inch long. 



Injury. -The first indication of the presence of these slugs is 

 the blister-like swellings on the upper surface of the leaves. They 

 have a wavy or crumpled appearance, due to the presence of eggs 

 in the under surface. From four to eight days are required for 

 hatching. These "worms" feed close together on the leaf, de- 

 vouring it entirely, leaving only the midrib. 



Life History. In ten days to three weeks the larvae become 

 full grown, descend to the ground, where they form shining, dark 

 brown cocoons composed of a glue-like secretion. In about a 

 week the adult saw-fly emerges. 



Control. Sometimes poplars and willows are defoliated by this 

 pest, but it is easily controlled by any good arsenical poison. 

 It is also attacked by Chalcid and Ichneumon parasites. 



The Mottled Willow Borer. This is a snout beetle (Crypto- 

 rhynchus lapathi Linn.) ,from one-third to three-eighths of an inch 

 long, with a dull-black body. It is an imported species. 



Injury. The white larva burrows around the buds and at 

 bases of small stems, which latter it may partly girdle. The 

 injury is indicated on the willows by a purplish discoloration of 

 the bark on either side of the burrow. The larva also bores into 

 the center of small stems, making galleries one-eighth of an inch 

 in diameter. It is reported as attacking willows, cotton woods, 

 birches, and alders, and is perhaps as much a pest of the poplar 

 as of the willow (Fig. 278). 



Control. All seriously infested wood should be cut and burned 

 in the early spring. 



Cottonwood Leaf Beetle (Melasoma scripta Fab.). This 

 beetle (Fig. 279) is found both on the willow and poplar, appear- 

 ing hi the early spring, contemporaneously with the leaves. It 

 shows a preference for tender snoots. Egg-laying begins imme- 

 diately, the eggs being placed on the under surfaces of leaves. 



The young grubs, upon hatching, skeletonize the under" sides 

 of the leaves and, as they get older, eat holes in the stem. When 

 alarmed, they exude a milky substance along their sides for their 



