THE TREATMENT OF INSECTS AND FUNGI IN THE UNITED STATES. 198 



effectual unless used in sucli quantities as to destroy the roots of 

 the plants at the same time, and this is practically useless, 

 except for disinfecting the soils. The very exhaustive and 

 unsuccessful experiments made with the phylloxera, especially 

 in France, make it appear doubtful if anything will ever be 

 found in the way of treatment for root insects. For annual 

 crops, the most promising methods at present known are crop 

 rotation, starvation, and trapping. 



Boring Insects. — About the only thing that can be done for 

 boring insects is to prevent their entrance into the plant. This 

 may be done by mechanical means, by covering the threatened 

 parts with something that will either prevent the egg-laying or 

 form a barrier to the young insect. Thus the use of cylinders of 

 wire mosquito net, an inch or two larger than the trunk of the 

 tree. Borers may also be prevented entrance by coating the part 

 of the plant liable to attack with some poison, which will be 

 eaten by the young borer as it attempts to burrow into the plant. 

 A good coating is a paint composed of glue made green with 

 " Paris green." For green parts of trees, Paris green with water, 

 applied often to keep the parts well poisoned, will be found a 

 good destroyer. After the insect has once entered the tree there 

 does not appear to be any sure cure.* 



Sap-sucking Insects. — In this category are included some of 



the easiest as well as some of the most difficult insects to destroy, 



but they can all be treated successfully as far as we know. It 



may be often that the cure will be too expensive to be practical. 



This would apply generally to field crops, where the cost per 



acre for treatment is greater than the saving that can ensue from 



the application. The insects of this class are not affected by 



poisons like Paris green, because they get their food by inserting 



their beak into the plant ; nothing, therefore, on the surface of 



the leaves will have any particular effect. The only feasible 



plan, therefore, is to spray on them some caustic or oily substance, 



or to envelop them with some poisonous gas. Plant lice are 



ordinarily very easy to kill, but protected insects, like the scale 



insects, or very active ones, like the so-called grape thrips, are 



far more awkward to deal with. The latter are probably best 



* The maggot or grub that bores in apple and pear trees may be easily- 

 detected by the excreta thrown out by the insect at the orifice it entered by. 

 If a pliable piece of copper wire is inserted with a little force the grub is 

 generally killed, and the branch or tree is but little the worse. — En. 



