

142 The Ottawa Naturalist. [Jan. 



each species has a limited number of food plants, but some, like 

 Pterocyclon mali, feed in many trees, both coniferous and decidu- 

 ous. 



According to their habits, the North American species of 

 Ipidae may be separated into four fairly well-marked groups:, 

 the Bark-beetles, the Timber- or Ambrosia-beetles, the Twig- 

 beetles, and a fourth group containing a few species of varying 

 habit. 



The Bark-beetles. The first of the above-named groups 

 includes those forms which burrow in the bark, or between the 

 bark and the wood. The adults enter through a hole in the 

 bark, cut in many cases by the male, and drive a primary-tunnel 

 between the bark and wood, usually partly in the bark and partly 

 in the wood, and frequently either parallel with or at right angles 

 to the wood-fibres. A few species burrow entirely in the bark, 

 and others, included here in the Bark-beetles, cut their tunnels 

 just below and parallel to the wood surface. The length 

 of the tunnel varies in the different species from less than an inch 

 to more than a foot. The female does the greater part of the 

 work, while the male guards the opening and removes the chips 

 and refuse. These main-tunnels are usually kept strictly clean. 

 In sweeping the tunnels the beetles move backwards, scraping 

 the refuse with the mandibles back to the fore legs, which pass 

 it on to the middle, and these to the hind pair. When the 

 opening of the tunnel is reached the tip of the abdomen is pro- 

 truded and the refuse passed up to the hind pair of legs in the 

 manner just indicated, and by the hind legs pushed away from 

 the opening. In cutting the tunnels the beetles constantly' 

 revolve,, and thus obtain such perfectly cylindrical burrows. 



When- not at work the male beetle is usually guarding the 

 entrance. By backing into the entrance-hole the declivity of 

 the elytra plugs the opening, and thus presents a complete 

 protection from many enemies. 



In niches along the sides of the primary -tunnel the whitish, 

 almost transparent eggs are laid, usually one, though sometimes 

 several, in each niche. In some species, I ps caelatus and Den- 

 droctonus simplex, several eggs are deposited in large niches; 

 while others, Hylurgops pin if ex and Dryocoetes autographus, 

 arrange the eggs in rows along the sides of the tunnel. 



When egg-laying is completed the adults of some species die, 

 and their remains may frequently be found long after in the 

 tunnel. Some species, however, cut a new tunnel and rear a 

 second brood. 



In those species which lay the eggs in masses along the sides 

 of the primary -tunnel, the larvae burrow in congress through the 



