32 INDIAN FOREST INSECTS 



slower than the much smaller bark-beetle ones. These grubs may take 

 six, eight, or ten months to reach full size in the bast and sapwood, and 

 then they will be found to have disappeared from view, as they will bore 

 tunnels into the sapwood or even into the heart-wood in which to pupate 

 (cf. pi. iv). Here they will remain for two or more months, and then 

 the mature beetle will crawl up the tunnel, eat a hole through the old 

 bark above, and escape from the tree. 



The gradual maturing of the pupa into the beetle can be ascertained 

 by chipping down one of the tunnels and exposing the elongate pupal 

 chamber at its lower end and observing the condition of the insect in it. 

 The mature beetle, from its colouring, hardness, and powers of movement, 

 will be readily distinguishable from the inanimate pupa or the still soft, light- 

 coloured, immature beetle. 



Thus it is evident that, whilst the first beetles observed to enter the 

 tree after felling, the bark beetles, may mature and leave the tree within 

 two months of its being felled, the slower developing buprestid and 

 longicorn beetles may require the whole year to pass through their life- 

 cycle. Consequently, these beetles will only be found on the wing in the 

 forest and egg-laying once in the year ; and should it not be their 

 egg-laying season when our first series of trees are felled, they will not 

 .appear in them, and may not appear until two or more series of our trees 

 have been cut. 



Two practical illustrations of this method of ascertaining the life 

 histories of insect pests in the forests may be quoted here. 



i. Life History of Sphaerotrypes siwalikensis, Steb. 



The life history of this scolytid bark-borer was worked out in the 

 sal forests of the Siwalik Division in the United Provinces. 



The observations were commenced in September 1901, when the 

 Divisional Officer, Mr. R. C. Milward, I.F.S., at my request kindly had a 

 couple of green sal-trees felled for me. 



The observations were carried out with the aid of the Range Officer, 

 and every fortnight until the following May, when the transfer of the 

 ranger led to their discontinuance for a time, visits were paid to the 

 trees, or the successive series of trees felled as required, and specimens 

 of all insects found in them were bottled and the tubes labelled and 

 sent in to me at Dehra. During this period I also visited the trees on 

 several occasions. Subsequent investigations undertaken between May 

 and September enabled the full observations for the year round to be 

 carried out. 



From these detailed investigations the life history of this important sal 

 bark beetle (see page 476) has been fully worked out, as also that of several 

 of its parasitic and predaceous foes. 



