U. S. D. A., B. E. Tech. Ser. 17, Pt. I. • F. 1. 1., June 30, 1909. 



CONTRIBUTIONS TOWARD A MONOGRAPH OF THE 

 SCOLYTID BEETLES. 



I. THE GENUS DENDROCTONUS. 



By A. D. Hopkins, 

 In Charge of Forest Insect Investigations. 



INTEODUCTORY. 



The active work on forest insects conducted by the West Virginia 

 Agricultural Experiment Station in 1890-91, and by the Division and 

 Bureau of Entomology of the U. S. Department of Agriculture since 

 1899, has resulted in the accumulation of a mass of systematic and 

 biological data on the principal described and undescribed insect ene- 

 mies of forest trees and forest products of the United States. When- 

 ever an attempt has been made, however, to work up the material 

 relating to a given species, or group of species, it has been apparent 

 that the publication of anything without first describing the new 

 species and revising the data in both the systematic and economic 

 literature would contribute to confusion rather than to advancement. 

 Indeed, it becomes more and more evident that in order to give reliable 

 information on applied entomology we must have at our command the 

 Icnowledge gained by careful technical, or systematic, studies of the insects 

 with which we have to deal. Therefore, when we find, as we do in many 

 cases, that the published results of systematic work on a given genus 

 or species are meager or otherwise unsatisfactory, it becomes necessary 

 to revise and verify the descriptions and biological records, and to 

 adjust the classification to meet the requirements of the newly dis- 

 covered facts relating to the described and undescribed species. 



The genus Dendroctonus presents a striking example of the need of 

 systematic study as a basis for economic investigation. It is both 

 the most important group of insect enemies of the coniferous forest 

 trees of North America and one of the most difficult for systematic 

 study. Le Conte (1876) expressed the difficulty met with in a study 

 of the species when he said in his later revision : 



If I have failed to indicate more strongly the differences between these species, it 

 is because they are not distinguishable by any prominent or definite characters; and 

 the student who may have difficulty in identifying the species as here defined would 

 have almost equal difficulty if the specimens in my collection were before him. 



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