FAMILY SCOLYTIDAE 461 



period than those laid at first. This results in a certain overlapping of the 

 generations, and this overlapping always occurs in practice. In damp, cold 

 seasons the overlapping is apparently greater than in dry ones, which are 

 much more favourable to the insects. 



In the majority of instances the beetles do not appear to feed to any 

 appreciable extent after issuing from the tree. They possess to a re- 

 markable degree that instinct which has already been described in the 

 case of the Cerambycidae, which enables them unerringly to detect newly 

 felled or standing sickly trees, and as soon as they issue from the tree in 

 which they have developed they fly direct to a tree in the condition 

 suitable for egg-laying. In some instances pairing takes place in crevices 

 on the outer bark, at others in a pairing-chamber prepared by the male 

 beetle inside the tree. The eggs, however, are rarely (in no instance in 

 the case of the Indian species known) laid on the outer bark of the 

 tree, or even in crevices in the bark, as is the case in the Buprestidae and 

 Cerambycidae. The beetles always tunnel down into the tree to oviposit. 

 The depth to which the beetle goes varies with different genera and 

 species. Pairing may take place outside the tree, the female subsequently 

 boring in to oviposit, or in other cases the male may eat out a pairing- 

 chamber in the outer thick bark, or down in the inner bast, or in the 

 outer sapwood. The female then either enters the tree by enlarging 

 the male entrance-hole, or tunnels a fresh one of her own which hits 

 off the pairing-chamber of the male. After fertilization here she carries 

 a tunnel down to the bast, and then bores away from the pairing- 

 chamber, grooving the bast or the bast and sapwood. Some bark beetles 

 are polygamous, and two, three, or more females may enter the pairing- 

 chamber of the male in this way, and, after fertilization, each carries 

 her own egg-gallery separately away from the pairing-chamber. In the 

 case of the wood-boring Scolytidae, i.e. those which oviposit in the sap- or 

 heart-wood, the tunnel into the sapwood is often eaten out by both male 

 and female, or commenced by the male and the female then enters it, is 

 fertilized, and continues the tunnel down farther into the wood. In this 

 latter work she may be aided by the male. 



It has been said that the beetles usually issue at night from the trees in 

 which they have been reared. Although this is often the rule, in the case of 

 several of the Indian species, Spliacrotrypes of the sal and 1'oly^i-iiplnis and 

 Tomicus of the blue pine and spruce, for instance, I have found tin- beetles 

 crawling about the bark of newly felled trees and tunnelling into them in 

 the daytime. This has generally been thecase, however, in areas where tin- 

 beetles have been unusually numerous. It is at such times that the latter 

 are preyed upon and consumed in large numbers by the pivdaceous clerid 

 beetle Thanasimus (p. 508). Some species, Poly\i;i\iplin* and Toinicus, espe- 

 cially the former, crawl with ease over the bark, whilst others walk but 

 feebly, and only appear really at home when in their tunnels. 



