30 



Insects Injurious to the Elm. 



haps more fatal, is a small beetle known as Scolytus destructor, 

 which, is shown below. It is affirmed by some naturalists that 

 this insect only appears upon a tree when a morbid or diseased 



A. The tunnel of cossonus linearis. 

 b. Cossonus linearis. 



1. Magnified larva of S. destructor. 



2. Larva of S. destructor. 



3. Greatly magnified head of S. 



destructor. 



4. S. destructor magnified. 



5. Size of S. destructor. 



growth has already taken place; but I have found small numbers 

 under the bark of apparently healthy trees. The first ravages 

 probably induce that morbid growth which renders the mul- 

 tiplication of the insect more rapid, as softening the wood and 

 bark, and rendering them more available as food. Scolytus 

 destructor is one of a group of insects which the German 

 naturalist, Ratzeburg, has minutely described in his Forst In- 

 secten (forest insects), a great work which he produced at 



the request, and under 

 the immediate patron- 

 age, of the Prussian 

 government. He has 

 figured in that volume 

 many species of this 

 genus and several al- 

 lied genera, besides an 

 immense number of 

 other insects injurious 

 to forest trees, exhibit- 

 ing them, in many in- 

 stances, in the larva, 

 pupa, and perfect 

 states, in order that 



No. l.-Tracks of Scolyti on the wood of the &restera may recog- 



elm. nize their enemies m 



all their stages. 



The two engraved specimens of wood injured by the Scolytus 



audits congeners, will show the manner in which they eat their 



