57 o FAMILY SCOLYTIDAE 



through the body of the insect and ejected. The white and yellow wood par- 

 ticles thus thrown out can easily be seen in little heaps on the outer bark. 

 When the beetle has finished egg-laying she does not die, but remains in the 

 egg-gallery or entrance-tunnel in the bark, both of which she keeps quite free 

 from wood-dust. The mother beetle may be found alive in the tunnel when 

 most of the larvae from the eggs she has laid have become full-grown and 

 are pupating. The beetle probably remains alive in order to protect the 

 eggs and larvae from predaceous insects such as the Niponius canalicollis 

 beetle (cf. fig. 331), who could otherwise enter the exposed gallery from the 

 outside to oviposit or destroy the larvae it contains. When she finally dies 

 it is usually in the entrance-tunnel in the bark, which she thus blocks up 

 effectually, as with a cork. The egg-gallery takes from five to seven days 

 to make. The larvae hatch from the eggs within a couple of days : young 

 larvae from the eggs first laid may be found already hatched out and boring 

 their galleries whilst the mother is still completing the egg-gallery above 

 and egg-laying. 



Between 70 and 85 eggs are laid in the egg-gallery, approximately 35 to 

 42 or 43 on each side. The larvae on hatching out bore in the bast and 

 sapwood ; they carry their galleries in a direction away from the egg- 

 gallery, those in the centre eating away in a direction more or less at right 

 angles, whilst the galleries of those above and below trend away from 

 the right angle in an upward or downward direction. In this way an 

 invariably uniform and constant pattern is made, which remains indelibly 

 impressed on the sapwood (cf. frontispiece and pi. Iviii). The presence 

 of the beetle in a forest is thus recognized and identified with ease from 

 these patterns which it leaves behind it in the trees it has attacked. 



The larval galleries curve irregularly to a slight extent, and increase in 

 size with the growth of the grub ; at the end where the larvae are full-grown 

 they are about the same width as the egg-gallery or slightly wider, and are 

 from 2\ in. to 2| in. in length. The galleries made by the larvae from the 

 first-laid eggs are the strongest-marked and often the longest. When full- 

 fed the larva changes to a pupa at the end of its gallery. In the case of 

 large trees the gallery may be slightly enlarged at the extremity, a small 

 depression being eaten out in the bark or sapwood. In poles, saplings, and 

 the upper parts of large trees the grub appears invariably to bore down into 

 the sapwood at the end of its larval gallery, eating out a small tunnel or 

 chamber of sufficient size to take its entire body ; having done this it backs 

 out from the chamber so made, turns round, and backs down into it again 

 and then pupates The larva takes about four weeks to reach full growth. The 

 tetle on maturing crawls out of the chamber and bores its way straight 

 through the bark of the tree and flies off to find a mate and, if a female, to 

 :ggs in a fresh tree. The time passed in the pupal stage is about two 

 the total period of a generation from egg to mature beetle being about 

 six or seven weeks. 



