10 



and in similar places. Aberrant habits are much more common in tropical 

 countries than with us. The vast majority of our species breed normally in 

 the bark or wood of trees. 



Details of the Tunnels. 



A study of the egg- tunnels and larval-mines reveals many important and 

 interesting characters. A distinctive form of the galleries obtains with 

 many species, so that an examination of the tunnels in the bark or wood may 

 determine exactly the species to which they belong. It is thus possible to 

 determine which species have been working in a tree, even years after the beetles 

 have left, and if the galleries were engraved upon the wood, even after the bark 

 has disappeared. The work of Chramesus icorioB Lee. in hickory branches 

 (PI. 23, fig. 5), of Leperisinus aculeatus Say in ash (PL 20, fig. 2), of Eccopto- 

 gaster picece Sw^ in spruce and fir (PI. 20, fig. 3), of E. rugulosus Ratz. in fruit 

 trees and wild cherry (PI. 5, fig. 7), of Phloeosinus canadensis Sw. in eastern 

 cedar (PI. 5, fig. 5), of Dryocoetes confusus Sw. in mountain balsam (PI. 19, 

 fig. 1), and many others, may be specificially determined, even though, as 

 rarely happens, no old dead beetles are to be found in the bark. 



THE ENTRANCE-HOLE. 



The entrance-hole with most species is usually free from chips or frass 

 except w'hile this material is being extruded; but with certain other species 

 there are peculiar characters connected with it. The boring-dust and excrement 

 of Xyloterinus politus Say projects from the entrance-hole while excavation is 

 active, often for several centimetres, as a cylindric rod of the diameter of the 

 entrance-hole. During a period of fine weather these are often visible in great 

 numbers on the trunks and limbs of dying, infested maples and beeches. The 

 entrance-holes of T. retusus Lee, on the other hand, are readily distinguished 

 by quite different characters. The opening is covered by a cup-like layer, an 

 aggregation of excrement. Through a small hole in the centre of this cup, 

 which is convex outwards, a slender thread of excrement projects, pushed out 

 by additions from within, until finally broken by rain or by the action of gravity. 

 The air circulation in tunnels so blocked at the entrance must be extremely 

 slow. The borings of Eccoptogaster rugulosus Ratz. and Phthorophloeus liminaris 

 Harris in green bark of peach trees and wild cherry trees result in a copious ex- 

 udation of sap, and the hardening of the sap produces conspicuous gummy 

 masses about the entrance-holes. The flow of resin from the tunnels of certain 

 species of Dendroctonus, Ips, and others, in green bark of pines and spruces, 

 results in a "pitch-tube" or "resin-tube" about the entrance-hole. The 

 beetles are able to live in spite of the exuding resin, and by their movements 

 backward and forward in the ejection of the boring-dust, form the surrounding 

 tower of gum upon the bark. The presence of this " resin-tube " about the 

 entrance-hole proves that the tunnel was started in fresh, sappy bark. 



With many species of Ipid beetles the male spends part of his time backed 

 into the entrance tunnel near the opening, which he neatly fits, and through 

 which his declivity is often visible. In species whose m^ales are wingless, and 

 therefore have no part in the construction of new tunnels, the female adopts 

 this function of guarding the entrance, in addition to her other regular 

 duties. With a few species, like Chramesus icorice Lee, one or other of the 

 parent adults dies in the entrance-hole, and thus prevents the intrusion of later 

 enemies. This closing of the entrance-hole for a considerable part of the time 

 guards in a measure from predacious and parasitic enemies, and checks evapor- 

 ation from the tunnel walls. 



