COLEOPTERA 



i73 



Fig. 306. 



groups, however, do not represent a natural division of the family based on 

 structural characters. The peculiar habits of the ambrosia-beetles are be- 

 lieved to have arisen independently in different parts of the series of 

 scolytid beetles. 



The Engraver-beetles or Bark-beetles 



If the bark be pulled from dead branches or trunks of trees, the inner 

 layer and the sap-wood will be found, in many cases, to be ornamented 

 with burrows of more or less regular form. The smoothly cut figures 

 are the mines of en- 

 graver-beetles, which 

 are also known as 

 bark-beetles. Many 

 kinds of these en- 

 gravings can be 

 found, each char- 

 acteristic of a partic- 

 ular species of 

 engraver-beetles. A 

 common pattern is 

 shown in Figure 306. 



The different species of engraver-beetles vary so greatly in the details 

 of their habits that it is difficult to make generalizations regarding them 

 in the space available here. In a common type, the adult beetle, after 

 penetrating the bark, makes a tunnel in the inner layer of the bark or in 

 the sap-wood or in both; this is known as the egg-tunnel, and may be 

 either simple or branched. In the sides of the tunnel, most species make 

 niches, the egg-niches, in which the eggs are laid. The larva when 

 hatched feeds on the bark or sap-wood or both and thus makes a lateral 

 tunnel. These lateral tunnels made by the larvae often extend parallel 

 in a more or less regular manner. 



While most of the engraver-beetles infest forest-trees, the two follow- 

 ing species are well-known pests of fruit-trees. 



The fruit-tree bark-beetle, Eccoptogaster rugulosus. 

 — This species infests apple, quince, plum, peach, and 

 other stone-fruits. It is sometimes called the shot- 

 hole borer by fruit-growers on account of the small en- 

 trance holes of its burrows. The adult beetle measures 

 from x 1 ^ to yV of an inch in length, and is dark brown or 

 nearly black. It infests chiefly sickly trees. 



The peach-tree bark-beetle, Phthorophlams limi- 

 naris. — This species resembles the preceding in size 

 and habits, except that its injuries are confined 

 chiefly to peach and cherry. It can be distinguished 

 from the fruit-tree bark-beetle by the fact that the club 

 of the antennas is lamellate, an unusual feature in this family (Fig. 307). 



The Ambrosia-beetles or Timber-beetles 



Certain members of the family Scolytidas differ in habits from the 

 engraver-beetles or bark-beetles in a remarkable manner; these are those 

 known as ambrosia-beetles or timber-beetles. They are termed ambrosia- 



Fig. 307. - 

 la-us liminaris. 



Phlhoroph- 



