558 FAMILY SCOLYTIDAE 



The life history of this Tomicus resembles to some extent that of 



T. ribbentropi, Stebbing, of the blue pine and spruce, 



Life History. but varies in a few important particulars. In attacking 



the tree the male beetle bores through the thick bark 



down to the bast, and eats out in the sapwood a squarish pairing-chamber 

 about half an inch by just under half an inch. Fig. i d in the plate shows a 

 male beetle in the pairing-chamber. A female enters by the same hole, and 

 after pairing bores away from the pairing-chamber in an upward direction 

 parallel to the long axis of the tree. A second, third, and fourth follow, the 

 third going in the same direction as the first, the second and fourth in an 

 opposite one. The egg-galleries so eaten out are very long, often as much 

 as three to five inches, or even more, in length. The female, as she eats out 

 her egg-gallery, carries one or more, normally two, aeration tunnels to the 

 outside ; these air-holes do not pierce the bark entirely, a thin lamella 

 of outside bark being left for protective purposes to prevent the ingress 

 of outside intruders, chiefly enemies, into the tunnel. 



The female egg-tunnel is always kept entirely free from sawdust, excreta, 

 and other wood particles. It grooves deeply the sapwood, and is usually 

 slightly serpentine in character. The eggs, some forty to sixty in number, 

 are laid in notches eaten in the side walls of the gallery, the larger number 

 being usually laid on the wall remote from the adjacent egg-gallery of the 

 other female. On hatching out from the egg the larvae eat out galleries 

 which are very winding and appear to have no definite direction, often being 

 inclined at an acute angle to the egg-gallery, and occasionally curving back 

 upon themselves as the grub approaches full growth ; the grub thus eats out 

 a much larger gallery than is required for its breadth. This larval gallery 

 chiefly grooves the inner bark, and is tightly packed with wood excreta 

 (pi. Ivi). When the insect has attacked a tree in numbers, the long main 

 egg-galleries and a mass of intersecting larval galleries tightly packed with 

 wood excreta almost entirely remove the bast layer. When full-grown the 

 larva enlarges the end of its gallery in the inner bark into a squarish irregular 

 pupal chamber and pupates in this ; this pupal chamber is the only portion 

 of the larval gallery which is free from wood-dust and excreta. On maturing 

 the beetle bores straight through the bark to the outside of the tree and 

 escapes. Observation would seem to show that the beetles mostly mature 

 and leave the tree in swarms at about the same time. For instance, in 

 some green trees blown down during the rains of 1906 (probably towards the 

 end of August), and examined in the middle of October 1906, the insect was 

 found in the immature, or nearly mature, beetle stage, in the upper parts of 

 the main stem of the tree, whilst in the thick lower parts of trunk and butt 

 where the bark was still green and fresh the newly issued beetles were tunnel- 

 ling in to lay the eggs of the last generation or partial generation of the year. 

 No pupae were found in these trees, and only a few belated grubs. Fig. i e 

 in pi. Iv shows several of these entrance-holes on the outer bark, and a beetle 

 just commencing to burrow into the tree. 



