58 SOME INSECTS INJURIOUS TO FORESTS. 



United States during the past century, and especially those that 

 have come under the observation of the writer and assistants engaged 

 in forest insect investigations during the past eighteen years, furnish 

 conclusive evidence that this class of enemies has been, and is now, 

 an important factor in the destruction and waste of forest resources. 



Insects Cause the Death of Trees. 



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 Avhole 

 forests of century-old trees having 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 {Dendroctonus frontalis Zimm.) extended 

 from the western border of West Virginia through Maryland and 

 Virginia into the District of Columbia, 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 thousands of acres 

 were killed, while shade and ornamental trees within the same area 

 suffered the same as those in the forest. Since 1902 this barkbeetle 

 has been more or less active in the Southern States from Virginia 

 to Texas, and in some localities and during certain years it has 

 killed a large amount of timber. Records of extensive destruction 

 of timber in the Southern States are found dating back to the early 

 part of the nineteenth century (Wilson, 1831). This species may be 

 considered one of the most dangerous insect enemies of southeastern 

 conifers and, therefore, a constant menace to the pine forests of the 

 Southern States. (Hopkins, 1899&, 1903&, 19095.) 



The eastern spruce heetle. — During the period between 1818 and 

 1900 there were several outbreaks of the eastern spruce beetle {Den- 

 droctonus piceaperda Hopk.) in the spruce forests of New York, 

 New England, and southeastern Canada (Peck, 1876, 1878; Hough, 

 1882; Packard, 1890; Pinchot, 1899, p. 74; Hopkins, 1901«, 19096). 



