INSECTS AFFECTING OAK-KOOTS. 49 



records for Germany. It is not improbable that ultimately the number 

 of species for the United States will be between 600 and 800 or even 

 1,000. 



W^ will now briefly indicate those species of insects which are habit- 

 ually more or less destructive to the oak. 



The roots of the live and probably the water oak are infested by the 

 great longicorn borer, Mallodon melanopus, the trees being permanently 

 dwarfed and their growth arrested. 



Of the borers in the trunk, the caterpillar of the Carpenter moth 

 {Prionoxystus robinice) probably does more damage than all other borers 

 combined. Next to this borer, come the flat-head borers, and the bark- 

 borers, with the oak-pruner [Elaphidion villosum), while the seventeen- 

 year Cicada periodically prunes or destroys many of the twigs. 



The leaves suffer most from the attacks of the forest tent-caterpillar 

 {Clisiocampa disstria) and the large black-and-red-striped spiny cater- 

 pillar of the senatorial moth {Anisota senatoria). These two caterpillars 

 in the Atlantic and Central States as a rule do more harm to oak for- 

 ests than perhaps all the other species combined. 



Finally, many acorns are worm-eaten, the intruder being the grub of 

 the long-snouted weevil {Balaninus). We have, so far as practicable, 

 described the habits and appearance of the most destructive species 

 first. 



AFFECTING THE ROOTS. 



The roots of various species of oak are, without much doubt, more 

 or less injured by the attacks of the seventeen-year Cicada while in its 

 preparatory state, as it is known that this insect, so abundant in the 

 central and southern States of the Union, remains for over sixteen 

 years attached by its beak to the rootlets of the oak and probably other 

 forest trees, where it sucks the sap, thus in a greater or less degree in- 

 juring the health of the tree. Observations as to the subterranean 

 life of the seventeen-year locust are few and obscure, and it is quite 

 uncertain how much injury is really done to trees by this habit. They 

 have sometimes been found sucking the sap of forest trees, notably the 

 oak, and also of fruit trees, snch as the pear and apple. According to 

 Riley (First Report, p. 24), the larvae are frequently found at great depth, 

 sometimes as mucli as 10 feet below the surface. It has been claimed 

 by Miss Margaret! a H. Morris, in an account published in 1846, that 

 pear trees have been killed by the larvae sucking the roots. This has 

 been denied by the late Dr. Smith, of Baltimore, who says: 



The larva obtains its food from the small vegetable radicels that everywhere per- 

 vade the fertile earth. It takes its food from the surface of these roots, consisting of 

 the moist exudation (like animal perspiration), for which purpose its rostrum or snout 

 is provided with three exceedingly delicate capillaries or hairs, which project from 

 the tube of the snout and sweep over the surface, gathering up the minute drops of 

 moisture. This is its only fooi. The mode of taking it can be seen by a good glass. — 

 Prairie Farmer, December, 1851. 

 5 ENT 4 



