Circular No. 125. issued November 25, 1910. 



United States Department of Agriculture, 



BUREAU OF ENTOMOLOGY. 

 L. O. HOWARD, Entomologist and Chief of Bureau. 



INSECTS WHICH KILL FOREST TREES: CHARACTER 

 AND EXTENT OF THEIR DEPREDATIONS AND METH- 

 ODS OF CONTROL." 



By A. D. Hopkins, 

 In Charge of Forest Insect Investigations. 



It has been conclusively demonstrated that certain species of insects 

 are the direct or primary cause of the death of forest trees of all 

 ages, and that from time to time they multiply to such an alarming 

 extent that their depredations assume the character of a destructive 

 invasion, which results in the death of a large percentage of the best 

 timber over thousands of square miles. 



There are many species of barkbeetles which prefer to attack 

 matured and healthy trees, and there are many examples of whole 

 forests of century-old trees that have perished from the girdling effect 

 of the mines of the beetles, which are extended in all directions 

 through the inner living bark on the main trunks of the trees. 

 Indeed, we find among these bark-boring beetles the most destructive 

 insect enemies of North American forests. Some notable examples 

 of the depredations of these barkbeetles are given below. 



The southern pine beetle. — In 1890-1892 a destructive invasion of 

 the southern pine beetle extended from the western border of West 

 Virginia through Maryland and Virginia into the District of Colum- 

 bia, northward into southern Pennsylvania, and southward into North 

 Carolina. In this area, aggregating over 75,000 square miles, a very 

 large percentage of the mature and small trees of the various species 

 of pine and spruce was killed by this beetle. In many places in West 

 Virginia and Virginia nearly all the pine trees of all sizes on thou- 

 sands of acres were killed, while shade and ornamental trees within 

 the same area suffered the same as those in the forest. Since 1902 



« Revised extracts from Bulletin No. 58, Part V, Bureau of Entomology, U. S. 

 Department of Agriculture, 1909. 



[Clr. 125] .1 



