FAMILY SCOLYTIDAE 477 



This Sphaerotrypes is the bark-beetle pest par excellence of the sal forests 

 of the United Provinces, and probably extends into the 



Life History. sal are^s in Nepal to the east. The beetle primarily 



infests the sal-tree, but is also to be found attacking 



Anogeissus lutifolia and Terminalia toinentosa. The insect is often found 



infesting the sal in company with the longicorn sEolesthes holosericea 



(p. 301). 



The beetle hibernates in the outer layers of the thick dead bark of the 

 larger sal-trees in the forest, tunnelling into the bark about half an inch. 

 The bark of large trees may often be found to be pitted with small holes in 

 the winter months, and if these are cut into, either this beetle will be found 

 Dr the predaceous histerid Niponins, which feeds upon it. The bark-borer 

 makes its first appearance in the year about the middle of March in dry 

 warm years, the beginning of April in cold wet ones. The insect is 

 gregarious, issuing from the trees in swarms and flying together to attack 

 fresh ones. The female usually pairs with the male in the outer bark of the 

 tree, the beetles boring in at separate points, the tunnels meeting in the 

 outer bark. After fertilization the female beetle continues her tunnel down 

 to the bast, and then eats out a gallery in this latter parallel to the long 

 axis of the tree, and grooving both bast and sapwood. In this gallery she 

 lays her eggs, thirty-five to forty in number, in little indentations made on 

 each side all the way up. It is possible that she pairs with the male more 

 than once, crawling back to the pairing-chamber at intervals during the con- 

 struction of the egg-gallery. The length of the egg-gallery is in. to i^ in. 

 The larvae on hatching out bore galleries away from the egg-gallery at 

 angles which deviate more and more from the right angle the nearer they 

 approach to the extremities of the female gallery (fig. 19, p. 33). The length 

 of the larval gallery is if in. or a little more. 



On becoming full-fed the larva, whose gallery grooves both bast and 

 sapwood, enlarges the end of its tunnel into a small chamber, and chango 

 into a pupa in this. The beetles on maturing leave the pupal chamber 

 by boring out horizontal tunnels straight through the bark to the outsit If 

 (fig. 310). 



Fig. 19 shows the plan of the galleries made in the bast and sapwood 

 by the female beetle and the larvae. This plan is always constant 

 for this beetle and never varies. As each larva bores out the pupating- 

 chamber of the future beetle at the end of its larval tunnel, and as 

 the tunnels are all more or less of the same length, if the outer bark 

 of the tree is examined after the new brood of beetles has left it a 

 roughly-shaped ellipse of exit holes will be seen upon it, as shown in 

 fig. 310. 



Owing to the pattern thus left in the outer bark by the exit-holes of 

 the new generation of the beetles, an examination of the bark of infest 1 

 trees will show whether the beetles being raised in the tree have left 

 or not. 



