REFERENCES 271 



his forest. It is imperative that he be always on the lookout 

 for signs of insect depredations and discover the attack before 

 it has reached a serious stage. There are various signs by 

 which insects reveal their presence, such as fine dust from 

 their borings on the ground or on tree trunks, holes in the 

 tree trunks, excrement, exudation of pitch, the withering or 

 coloring of foliage, a bare appearance of the tree tops, bitten 

 off and partially devoured foliage on the ground, and the 

 presence in the stand of an unusually large number of in- 

 sectivorous birds. 



REFERENCES 



1. Hopkins, A. D. Insects in Their Relation to the Reduction of Future 

 Supplies of Timber, and General Principles of Control. Circular No. 129, 

 Bureau of Entomology, U. S. Department of Agriculture, Washington, 1910. 



2. Pearce, W. J. The Relation of Insect Losses to Sustained Forest 

 Yield. Journal of Forestry, Vol. XVIII, 1920, pp. 406-411. 



3. Hopkins, A. D. On the Study of Forest Entomology in America. 

 Bulletin 37, N. S. Division of Entomology, U. S. Department of Agriculture 

 (Proc. 14th Annual Meeting Assn. Econ. Ent.), Washington, 1902, pp. 20-25. 



4. Hopkins, A. D. Notable Depredations by Forest Insects. Yearbook 

 of U. S. Department of Agriculture for 1907, Washington, 1908, pp. 149-164. 



5. FuRST, H. The Protection of Woodlands, translated by John Nisbet, 

 Edinburgh, 1893, pp. 129-130. 



6. Fisher, W. R. Forest Protection. Schlich's Manual of Forestry, 

 Vol. IV, London, 1895, p. 140. 



7. Report of the Entomologist for 1919. U. S. Department of Agri- 

 culture, Washington, 1919,' p. 12. 



8. Hopping, Ralph. Manual of Insect Control for California District 5, 

 1914. Manuscript. 



9. Reiff^ William. The Wilt Disease or "Flacherie" of the Gipsy 

 Moth. Published under the direction of F. W. Rane, State Forester, Boston, 

 Mass., 1911. 



10. Felt, E. P. Insects Affecting Park and Woodland Trees. New York 

 State Museum, Memoir 8, 2 vols. Albany, 1905-06. (Includes BibUography 

 for each of the insects described.) 



11. Hopkins, A. D. The Dying of Pine in the Southern States: Cause, 

 Extent and Remedy. Farmers' Bulletin No. 476, U. S. Department of Agri- 

 culture, Washington, 1911. 



12. FiSKE, W. F. The Gipsy Moth as a Forest Insect, with suggestions 



