154 TEEES IN" WINTER 



the way of preventing injury by keeping trees growing vigorously. 

 A strong-growing tree is better able to withstand the attack of in- 

 sects than a decrepit one. Some insects, like the bark-beetles, cause 

 serious injury to weakened trees, while they seldom affect vigorous 

 specimens. The burning of infested branches, leaves, fruit or other 

 rubbish where insects are likely to hibernate will destroy many 

 pests and lessen the severity of the attack in succeeding seasons. 



Natural Enemies of Insects — Much may be done, also, to guard 

 against insect depradations by protecting the natural enemies of 

 the insects. In sections where birds are allowed to collect and are 

 encouraged to nest, the excessive development of insect pests is pre- 

 vented. Injurious insects also have many enemies among their 

 own kind. It is a common occurrence to see a large caterpillar 

 almost completely covered with small white bodies. These are 

 the cocoons of a parasitic insect, the earlier stages of which have 

 been spent within the host insect. Caterpillars thus, affected some- 

 times survive, but are usually too weak to complete their develop- 

 ment. Insects affected in this way should not be destroyed by 

 man, for in doing so he also destroys many useful parasites. 



Some insects are attacked also by certain fungus diseases that 

 exert a marked influence on keeping the pest under control. Owing 

 to the influence of a fungus parasite, the gypsy moth in its 

 native home is not a serious pest. AYhen the insect was accident- 

 ally imported the fungus parasite was left behind, hence the 

 seriousness of the j^est in this country. A representative of the 

 United States Department of Agriculture, a short time ago went 

 to Japan and brought back come cultures of the parasitic fungus. 

 Efforts are now being made to encourage the development of the 

 disease amidst the gypsy moths of Maasschusetts. 



There are many other examples of insects having been imported 

 without their natural enemies, and among these are the most serious 

 pests of trees, such as the San Jose scale, the leopard moth, the 

 brown-tail moth, and the elm-leaf beetle. Such serious pests as 

 these and some fungus pests, also, have been imported on nursery 

 stock and might have been avoided by an adequate system of in- 

 spection. Some form of legislation is badly needed for the pre- 

 vention of infested nursery stock coming into this country. 



SOME COMMON SHADE TREE INSECTS 

 To prescribe the proper treatment for the control of any particu- 

 lar pest, it is necessary to be able to identify the species causing 



