BARK-BEETLES. 237 



make regular galleries, but merely enlarge the egg chambers in 

 the wood of the tree, and the mature insects escape through 

 the bark by the original boring made by the mother. 



Bark-beetles are specially addicted to conifers, and most of 

 these species are monophagous. An occasional departure 

 which they may make from this rule is to be looked upon as 

 an exception due to local circumstances. There are also 

 numerous species of these insects which feed solely on coni- 

 ferous trees or on broadleaved trees, but without attaching 

 themselves exclusively to a particular kind of tree. Even the 

 few polyphagous species show an individual preference for 

 either coniferous or broadleaved trees. There are no panto- 

 phagous bark-beetles, which eat herbaceous as well as woody 

 plants, whilst those which only attack herbaceous plants are 

 very few in number and without interest to the forester. 



Bark-beetles prefer freshly felled stems, but also attack 

 standing trees; they then commence their attacks on sickly or 

 injured stems. A certain degree of warmth is necessary for 

 them, and the flight of, e.g., Tomicus tiipograplms, L., begins 

 only when the air temperature is G8° F. Even the hardy 

 B. cliahjdtirapJius, L., requires a temperature of 61° F. 



This family of the Coleoptera is generally regarded as the 

 most important which the forester has to guard against, owing 

 to the large number of very injurious species which it con- 

 tains. Fortunately, many of these are unknown in Britain, 

 or are so rare as never to have been classed among our 

 destructive insects. 



Judeich and Nitsche distinguish the subfamilies of injurious 

 bark-beetles as follows : — 



Toiiiicini. True bark-beetles: Head hidden beneath the 

 prothorax. Anlennal funiculus 2 — 5-jointed. Tarsal joints 

 simple. Apical declivity prominent and generally toothed. 



Hijlesini. Bast-beetles : Head prominent, not concealed 

 beneath the prothorax. Antennal funiculus 5 — 7-jointed. 

 Third tarsal joint usually bilobed. Apical declivity without 

 teeth. 



Scohjtlni. Sap wood-beetles : Head prominent. Antennal 

 funiculus 7-jointed. Third tarsal joint bilobed. Scarcely any 

 apparent apical declivity. 



