THK CANADIAN KNTOMOLOGIST. 253 



In two genera, Platypus and Xyleborus, the eggs are deposited free 

 in the tunnels. The larvse of Platypus live free in the tunnels until nearly 

 ready to pupate, when pupal cells (cradles) are cut from the sides of the 

 tunnels deep within the wood. 



The larvae of Xyleborus live and pupate within the parent tunnels 

 without cutting pupal cradles. In Corthylus, Trypodendron, Pterocyclon 

 and Gnathotrichus the eggs are laid in shallow niches cut by the female 

 along the sides of the tunnel, and usually well within the wood ; the larvae 

 extend these niches away from the tunnel, forming larval cradles, in which 

 they remain until mature. The length of the completed cradles is slightly 

 greater than that of the adult beetle. 



The adults of the Ambrosia-beetles bestow great care upon the young 

 larvae, supplying them with the food-fungus, referred to below, and 

 removing the e.xcrement from the cradles. In some species even older 

 larvje assist m caring for the eggs and younger larvaj. The habits of 

 many species are almost as remarkable in this respect as are those of the 

 social Hymenoptera. 



The chief and probably the entire food of these beetles is a fungus 

 known as Ambrosia, which they propagate within their tunnels. From 

 this habit comes the name '• Ambrosia-btetles." 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 all 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 upon specially-prepared 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. 



An excellent discussion of the habits of the Ambrosia-beetles, by Mr. 

 H. G. Hubbard, is published in Bulletin No. 7 of the U. S. Division of 

 Entomology. 



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 shrubi both for food and for breeding purposes. They feed upon the 



