236 PROTECTION AGAINST INSECTS. 



Generation : usually annual, sometimes biennial, or extend- 

 ing over a year and a half. Larvae cylindrical, curved, with 

 tubercles bearing strong hairs, apodal, and. closely resembling 

 the larvae of weevils. 



Pupae short and thick, with a few spines and hairs. 



The larvae and beetles live almost exclusively in the bark, 

 bast or wood, more rarely in the pith, of our forest trees. They 

 attack roots, stems, branches, twigs and young shoots, and 

 young or old wood, preferring the latter. The kind of tree 

 which they attack, and the arrangement of their borings, is 

 usually characteristic of each species. The beetles penetrate 

 into the trees by boring a small entrance-hole, like a shot- 

 wound, through the bark. This is usually accomplished by 

 the ? , but in some polygamous species the $ enters the tree 

 and excavates in the bark a small pairing-chamber. From 

 this chamber, or from the entrance-hole, proceeds the gallery, 

 which is made by the , and in the outer surface of which a 

 few air-holes may be perforated. The galleries may be divided 

 into those constructed in the bark or alburnum, parallel to the 

 exterior surface of the tree, and those which run more or less 

 vertically into the wood ; the former may be subdivided into 

 longitudinal or transverse simple galleries, forked galleries, or 

 stellate galleries, the latter being formed by several ? boring 

 radially outwards from the circumference of a pairing-chamber. 

 The form of the gallery is in the main constant for each 

 species, but may be modified by the size of the stem which is 

 attacked, by the absence of knots, etc., or by the over- 

 abundance of insects boring in the same trunk. The ? lays 

 her eggs as a rule in small hollows bitten out alternately on 

 each side of the gallery she is gradually excavating, packing 

 them in with wood-dust. The larvae, after hatching- out, eat 

 galleries which radiate from the breeding gallery, becoming 

 gradually wider with the growth of the larvae, and filled with 

 wood-powder ; they pupate in a chamber formed at the end of 

 the gallery either in the bark, bast or sapwood. Finally the 

 beetles eat their way out through round holes -flight-hole* 

 of the diameter of their own bodies. 



This is the general mode of life of the bark-beetles. The 

 larvae of those few species of Scolytidae which eat wood do not 



