468 FAMILY SCOLYTIDAK 



These wood- boring Scolytidae ma}' be monogamous or polygamous, 

 though in the majority of instances known the Indian species appear to be 



monogamous. 



In manv cases the winter is passed by Scolytidae either in the larval, 

 pupal, or resting beetle stage, in the gallery or pupal chamber. If the grub 

 has pupated and a severe cold winter is experienced, most of the pupae will 

 probably be killed in the case of the bark-boring insects. If the beetle has 

 matured and left the tree and a cold snap supervenes it bores a short 

 way into the thick bark of old trees and hibernates here (cf. Sphaerotrypes in 

 the sal, p. 477). 



The family contains numerous species in India which are very destruc- 

 tive to trees, and research into the habits of the family 

 Family * s showing that the beetles, especially the bark-boring 



forms, play a very important part, and will play a still 

 more important part in the future, in the economic life of the Indian forest. 



The real danger to the tree occurs in the case of the groups which 

 oviposit in the bast layer. Damage is done here by both beetle and larva, 

 the former grooving out the egg-gallery whilst the latter eats out an offset 

 gallery. A certain amount of the bast is thus removed by each. Con- 

 sequently when a tree is attacked by a large number of beetles, thousands of 

 egg-galleries may be eaten out in the bast. From each egg-gallery twenty to 

 seventy or more larval galleries may take off, and may cover the whole of the 

 main stem of the tree from base to the crown. In such cases the galleries 

 when complete form an interlacing mass, practically the whole of the bast 

 disappears, and the tree dies. This is a common feature of the attacks of the 

 Scolytus in deodar, Toniicus and Polygraphus in blue pine, spruce, and long- 

 leaved pine, and Sphaerotrypes in the sal. Under Scolytus major figures are 

 given (p. 572) to show the large number of beetles which are reared in one 

 tree under these conditions. 



Bark beetles do not usual!}' attack green trees unless driven to do so. 

 For ovipositing purposes they seek out newly felled trees, windfalls, snow- 

 broken tree?, or standing sickly trees whose vitality has been reduced from 

 one cause or another. In all cases the trees must possess absolutely fresh 

 sappy bast, or the beetles will not oviposit in them. Felled trees or wind- 

 falls which have lain for a couple of months exposed to the rays of the hot 

 Indian sun will not be attacked, and it would appear that the beetles will not 

 oviposit in trees which have been felled or have fallen in thick shade. Should 

 a supply of trees in the condition required by the beetles not be forthcoming 

 on an area, the insects will attack green standing trees. The first series of 

 beetles to infest the trees will in all probability be drowned in their partially 

 constructed burrows by an outflow of sap or resin put forth by the tree. 

 The tree responds with this outflow to each succeeding attack as long as its 

 vitality enables it to do so. Should the number of beetles in the forest be 

 excessive, succeeding attacks are successful and the tree is killed. Thus the 



