Insects Injurious to Elm Trees. 



By E. P. FELT, D. Sc, State Entomologist. 



NEW YORK STATE MUSEUM. 



UNIVERSITY OF THE STATE OF NEW YORK. 



'HE number of insects attacking one tree or a closely related group of trees 

 is so great, that it is practically impossible to notice all such forms in a 

 brief paper, consequently this account will be limited, like its predecessor 

 on insects affecting maples, to a few of the more injurious species. Some 

 of those mentioned in the previous report injure elms most seriously and in a 

 similar way a number of insects treated of in this are very injurious to maple 

 trees. These two papers are in a degree supplementary to each other, though 

 independent. 



Methods of controlling insect pests. The habits of injurious insects are so diverse, 

 that it may be well at this time to consider briefly a few principles of general appli- 

 cation before treating of certain species. Practical considerations compel the recog- 

 nition of two classes of insects, the biting or devouring and the sucking species. 

 Generally speaking, the former can be controlled by spraying infested plants with 

 arsenate of lead, paris green, london purple or other arsenical poisons. The aim of 

 such treatment is to cover the plant so thoroughly with the substances used that it 

 will be practically impossible for the pest to feed without also consuming the deadly 

 insecticide. Experiments have shown more than once that caterpillars will not feed 

 on foliage sprayed with poison till forced to do so by hunger, while those placed on 

 untreated leaves, with all other conditions the same, manifest no such hesitancy. 

 Thus it is pretty safe to assume that insects will not eat poisoned leaves unless 

 obliged to do so or go hungry, and that only the most thorough spraying will pro- 

 duce satisfactory results. Measures of value against leaf devourers may not have 

 the slightest effect on those forms which obtain their nourishment by sucking, 

 through a slender beak, the fluids from the underlying plant tissues. The work of 

 biting insects is characterized by the removal of more o r less tissue from the part 

 attacked, while sucking insects never do this, though they frequently cause wilting 

 and discoloring in the immediate vicinity of the injury. Particles of paris green or 



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