46 Disease and Death of Trees — Generalities 



While some insects are general feeders, i.e., attacking all 

 kinds or at least a number of tree species, insects, even more 

 than fungi, are partial in selecting their hosts, i.e., given 

 species of insects attack given species of trees. Besides, 

 they differ much more in their life habits than fungi, hence 

 they may not be dealt with as a whole, like the fungi, but 

 it becomes more needful to know them specifically by name, 

 a])pearance, and habit, with their hfe history, in order to 

 apply judiciously measures for their reduction. Moreover, 

 there are a number of enemies of the obnoxious insects 

 found in the insect world, and it becomes necessary to dis- 

 tinguish between friend and foe, in order not to destro} the 

 natural enemies of the pesl. 



We can here refer specifically only to the more common 

 pests of ornamental and shade trees, leaving the vast num- 

 ber of minor and of orchard pests to be studied in the specific 

 literature. Fuller descriptions will be found in Chapter 

 VI; here only the character of the damage in general is to 

 be discussed. 



With regard to the manner m w );c'. j; ■, • Mnagc is inflicted, 

 we can classify the injuriou • insects into ;i few groujxs, each 

 group containing represents ■.arious orders into 



which insects are scientific a;i) classified. Those groups 

 may be called leaf-eaters, leilf-miners, leii.f-rollers, leaf- 

 suckers, gall-insects, bark-lice, bark-beetles and borers. 



The character of the danage itself may be threefold, 

 namely, destruction of substance, occasioned by leaf-eaters, 

 bark-beetles or borers; loss of sap occasioned by plant-lice; 

 and formation of abnormal excrescences or galls, to which 

 the plant is stimulated by various insects. AH three kinds 

 of damage or any two may be occasioned by the same ])est. 



The leaf-eaters are mostly caterpillars of butterflies and 

 especially of moths, which in feeding on the foliage generally 



