112 The Ottawa Naturalist. [Dec. 



The adults of the Ambrosia-beetles bestow a certain amount 

 of care upon the young larvae, furnishing them with the initial 

 supply of food-fungus, referred to below, and removing the 

 excrement from the tunnels outside the cradles. 



The chief food of these beetles is a fungus known as 

 Ambrosia, which they propagate within their tunnels. From 

 this habit comes the name "Ambrosia-beetles." The tunnels 

 are kept entirely free from chips and refuse, and the walls are 

 covered by the fungus growth. So far as known, except in the 

 cases of a few closely-allied forms, each species of beetle uses a 

 characteristic species of fungus. The mycelium of the fungus 

 pervades the tissue about the tunnels for one or two millimetres, 

 colouring the wood dark brown or black, so that the tunnels 

 have the appearance "of having been bored with a red-hot wire." 

 By this means the tunnels of Ambrosia-beetles are easily 

 distinguished from those of other wood borers. When new 

 tunnels are cut, the fungus is carried there by the beetles, and 

 started upon the tunnel walls, in some cases in specially-prepared 

 tunnels upon beds of chips and excrement. 



When working in large trees some species enlarge the same 

 set of tunnels through several generations; but usually each 

 generation excavates a new abode in dying parts of the same 

 or other trees. 



Very few of our timber-beetles enter healthy wood; almost 

 invariably they select trees in which the sap is unhealthy, at 

 least in the portion attacked. Their tunnels admit fungi to the 

 deeper layers of wood, and ruin the timber for the most valuable 

 uses. 



The Twig-beetles. The Twig-beetles include a few species 

 belonging mainly to the genera Hypothenemus, Pityophthorus 

 and Micracis. They bore into the bark and wood of terminal 

 twigs of trees and shrubs both for food and for breeding purposes. 

 They feed upon the bark and wood, and in some cases apparently 

 upon buds and young shoots. Some engrave the wood surface 

 as do the Bark-beetles; some have in addition deep chambers 

 within the wood; and with others the primary tunnel is cut 

 through the pith itself. With some species the eggs are laid free 

 in the primary tunnels, and the larvae either feed upon the tunnel 

 walls or cut longer or shorter mines through the wood. Several 

 species of this group have a very close relation to a fungus always 

 found in their tunnels. 



A summary of the borrowing habits of these first three 

 groups brings out some interesting relations. Among the Bark- 

 beetles the eggs are usually laid in niches along the sides of the 

 primary tunnels, and the larval mines are usually well-developed. 

 A few species cut their tunnels and mines entirely in the bark; 



