172 



THE STUDY OF INSECTS 



The species of this genus attack many kinds of conifers and deciduous 

 trees. They bore deeply into the heart-wood, making " pin-holes " that 

 often render lumber useless. The eggs are deposited in the galleries; 

 and the larvae feed on a fungus, which is cultivated by the beetles and is 

 known as ambrosia. In this respect Platypus resembles several genera of 

 the Scolytidae, which also bore in solid wood and feed on ambrosia; all 

 of these are known as ambrosia-beetles. The galleries of ambrosia-beetles 

 are usually blackened by the fungus. See further account of the ambro- 

 sia-beetles in the discussion of the next family. 



Famil y Scolytidae 



The Engraver-beetles and the Ambrosia-beetles 



The members of the family Scolytidae are mostly of cylindrical form 

 (Fig. 307) and of small or moderate size; some species measure only 

 ■^s of an inch in length, but others are much larger, attaining a length of 

 I of an inch or more. They are usually brown, 

 sometimes black, and with many the hind end 

 of the body is very blunt, as if cut off. The an- 

 tennae are elbowed or bent in the middle, and are 

 clubbed at the tip; the tibiae are usually serrate; 

 and the first segment of the -anterior tarsi is shorter 

 than the second, third, and fourth together. 



A few members of this family infest herbaceous 

 plants; our most important one of these is the 

 following. 



The clover-root borer, Hylastinus obscurus. — 

 This pest was introduced from Europe and has 

 become the most serious enemy of clover, especially 

 red clover and mammoth clover, in New York 

 State and in other sections of the North. It bores 

 in the roots of plants beginning their second year 

 of growth and destroys them (Fig. 305). Where 

 it is common it is practically impossible to keep 

 fields in clover longer than the second summer 

 after seeding. In these regions it is the common 

 practice to seed with clover and timothy mixed; 

 after the clover disappears the field becomes a 

 timothy meadow. No practical method of control 

 of this pest has been found. 



Most scolytid beetles infest woody plants; 

 among them are some of the most destructive 

 enemies of forest-trees, and a few attack fruit- 

 trees. As a rule they are more liable to attack- 

 sickly trees, but their injuries are not confined to 

 these. 



The scolytid beetles exhibit two radically 



different types of habits; and from this point of 



view they can be grouped into two groups: first 



the engraver-beetles or bark-beetles; and second, 



7jE k wK«T the ambrosia-beetles or timber-beetles. These two 



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