FAMILY SCOLYTIDAE 46; 



most direct route to the outside. There is thus left indelibly imprinted in the 

 bast and sapwood, or in the sapwood, or partly in one and partly in the other 

 (the female gallery often grooving both bast and sapwood, whilst the larval 

 galleries are entirely in the bast, as in the case of the Tomicus of spruce and blue 

 pine), a " plan " consisting of the mother and larval galleries of the species. 

 For any one species this plan is always the same, and an examination of 

 these old plans thus left imprinted in the trees will always enable the former 

 presence in the forest of this particular beetle to be definitely ascertained 

 long after the insects themselves have left the trees. This is a point of the 

 very greatest importance to the forester. The shot-holes on the outer bark 

 of the tree, made by the beetles entering the tree and by their offspring 

 tunnelling out of the tree on maturing, will tell the forester that bark beetles 

 are present in the forest, but they will not enable him to decide the species 

 present. By stripping off the bark he will be able to determine by the 

 "plans" left in the bast and sapwood the actual species which performed 

 the damage, should it be a bast beetle. 



These plans made by Scolytidae in their operations in the tree group 

 themselves into four distinct series of figures, according to the method 

 of oviposition by the parent beetle and the mode of feeding of the grubs. 

 The bark forms i.e. those members of the family which lay their eggs in 

 the bast layer of the tree as distinguished from the true wood-borers will be 

 first considered. 



The true bark-borers include both monogamous and polygamous forms, 

 and the plans of the galleries made by each are very different in appearance 

 and easily recognizable. 



The Indian monogamous forms are typically represented by the deodar 

 Scolytus (p. 568), and the sal Sphaerotrypes (p. 476). The female beetle 

 pairs with the male either outside or in the bark of the tree. In the first 

 case the tunnel down through the bark may be commenced by the female, 

 who then attracts the male near the entrance-hole, is fertilized by him, and 

 then continues her tunnel down to the bast. This is the usual habit of the 

 deodar Scolytus. In the second case the male bores a short way down 

 through the thick bark of the tree and eats out here to one side a small 

 pairing-chamber. The female crawls down this short entrance-tunnel or 

 makes a short tunnel of her own which exactly hits off the pairing-chamber 

 (cf. fig. 318, c, e,fon p. 482), pairs with the male in the pairing-chamber, and 

 then continues the tunnel straight clown to the b:ist layer. In each case, on 

 reaching the bast the female proceeds to eat out a g.illrry in the bast which 

 may be straight or may incline first to one side and then to the other 

 (cf. Scolytus major, fig. 307). The gallery is usually carried up the tree 

 parallel to its long axis, and may groove both bast and sapwood. As this 

 gallery is eaten out the female gnaws little notches in it on each side 

 at close and more or less regular distances apart, depositing in each an egg, 

 surrounded by a little mass of fresh, soft wood-dust, which is placed in 

 position with the hind feet. The beetle takes several days, up to a week 



