Book VII. 



NOXIOUS INSECTS. 



1117 



{fig. 972. a, d), that their form cannot be well distinguished without the aid of a magnifying glass ; many 

 of them resemble small scales or scabs fixed on the bark and shoots. One is entirely of a brown colour 

 (Coccus persicbrum a) : when magnified (6) it somewhat resembles the tortoise beetle (Cassida L.), the legs 

 and head being only discernible when the insect is turned on its back (c). Another (C. fbl. qufercus. 



972 



rf, e, e)does much injury to the oak ; while the C. fagi attacks the twigs of the beech (gr), and causes 

 email round excrescences to appear ; these are, however, very different from the gall apples of the oak {j ) 

 which are often found of a considerable size, and are produced by the Cynips quercus fijlii L. ( k), or 

 oak gall-fly, and always contain either the larva or imperfect insect. The weevils (Curculi6nidjE) form an 

 exceedingly numerous family, subsisting principally upon fruit, seed, and grain. One of the largest found 

 in this country is the nut-weevil {C. nCicum, fi,g. 970.e, e), the larvae of which (c, d) are the maggots so fre- 

 quently found in this fruit. 

 7^1. The insects injurious to plantations are less numerous in this country than on the Continent, yet 



973 



we have two species whose devastations of late years have caused 

 much alarm and extensive injury. The pine plantations in 

 various parts of Britain have suffered from the great saw-Hy 

 (Urocerus gigas La/.), the larvaof which, feeding upon the heart 

 of the tree, and boring it in all directions, soon destroys it. Another 

 small insect of the beetle kind (Scnlytus destructor F.,fig. 973. d 

 magnified) is equally deadly to the elm ; and from beingmore com- 

 mon, and propagating very rapidly, is more to be dreaded. The 

 sudden destruction of a large proportion of the elms in St. James's 

 and Hyde Parks has recently called the attention of government to 

 this beetle ; and at the request of the noble rangers, Mr. Macleay 

 undertook to investigate the evil : the result of his observations 

 have been since published {Edinb. Phil. Journal, No. 21.). It ap- 

 pears that the female [a) may be found upon the trunk of the elm 

 from March to September : she first penetrates through the bark, 

 and then proceeds to form a passage between that and the wood, 

 depositing her eggs during her progress on each side; when these 

 are exhausted, the parent dies, and is often found dead at the 

 extremity of the passage ifi) thus formed. When the eggs are 

 hatched, the young larva3 immediately begin to feed by working 

 nearly at right angles (cc) from the path of the parent, each pro- 

 ceeding in a parallel direction and close to his neighbour : in this 

 state they may be found in January. To stop this mischief as 

 much as possible, Mr. Macleay recommends that the trees should 

 be inspected twice a year : in summer, when the perfect insect is 

 on the wing; and again in winter, when infected trees should 

 be cut down and burned, or subjected by fumigation to such a 

 degree of heat as may destroy the larvae ; or the bark may be 

 covered with a mixture of tar and train oil, in March, to a certain 

 l\eight from the ground, applying this composition only to such 

 trees as there are still hopes of preserving. 



