402 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



willow. During the summer its large, green, slug-like larvae would be 

 met with from time to time, but not until the present summer have I 

 learned that it appeared in such great numbers as to completely de- 

 foliate the trees. 



About three weeks ago (August 31) I visited Mr. G. M. Dodge, of 

 Glencoe, Dodge County, and while driving across the country observed 

 that nearly every hedge of this willow had been more or less injured 

 by some insect which had stripped the trees of most of their leaves. I 

 at once attributed the work to the striped cottonwood beetle (Plagiodera 

 scripta), which, as you have shown, has been known to injure various 

 species of willow, as well as the poplars and cottonwood in this and 

 other sections of the country. Upon speaking to Mr. Dodge in reference 

 to the subject, he informed me that the work was that of the above- 

 named saw-fly. He also stated that the larvae had been so numerous 

 on many of the hedges in his immediate neighborhood as to completely 

 defoliate the trees before they (the larvae) had attained full growth, and 

 that they had therefore proved the cause of their own destruction. 



At other points, however, where the larvae were less numerous, they 

 have matured, and will evidently make their appearance in force next 

 season, provided no unforeseen providence intervenes. 



Mr. Dodge also informed me that this saw-fly has been steadily on 

 the increase for the past three or four years- — always working on the 

 white willow in preference to the native species. 



Another insect, and one that has been attracting general attention in 

 portions of this and other Western States and Territories by its greaj 

 abundance and general destructiveness to the cottonwood, poplars, and 

 willows, is the Streaked Cottonwood Leaf-beetle (Plagiodera scripta). 



The mature insect as well as the larvae feed alike on the younger and 

 more tender leaves and twigs, and thereby cause the tree to die in course 

 of time if the attack be continued several years in succession. When 

 the beetle is very numerous, all the leaves are eaten, and even the ten- 

 der bark, upon the new growth, devoured. When this last is the case 

 the trees have been known to die in a single year. This latter feature 

 but seldom occurs, even when the season is very dry and the trees have 

 been stripped. 



There is a remedy in nature by which it is kept under control, viz., 

 wet seasons following dry ones. Natural enemies are also doing much 

 towards checking the otherwise enormous increase of this insect, and if 

 left alone would very effectually reduce the pest during ordinary 

 years. These are very nearly identical with those attacking the Colo- 

 rado potato beetle. Among them various species of our common lady- 

 birds (Coccinellida) are the most efficient. Their work is mostly con- 

 fined to the destruction of the eggs, and perhaps a few of the newly- 

 hatched larvae. 



As for birds, I have never known of their capturing and eating the 

 beetle in any of its stages of growth, nor have I conversed with any 

 one who has seen them do so. 



The beetle is more highly favored on elevated, somewhat arid, ground 

 \vhere the tree growth is small and the temperature is low, than on low 

 ground, where the conditions are the reverse, though it often thrives for 

 a time even here. Bank growth in a tree thus affected is an advantage 

 against the insect, and trees of this nature are seldom, if ever, killed 

 by it. 



I have always found this beetle to be more common near the mount- 

 ains and upon the elevated plains of the West than elsewhere* 



