466 



FAMILY SCOLYTIDAE 



sustenance will be obtained if it attempts to tunnel in the direction of 

 the mother gallery. 



The larval galleries are always — and this is also the case with the 

 monogamous larvae — blocked with excreta and triturated wood particles 

 which have passed through the larval body. When full-fed the grubs pupate 

 either in the enlarged end of the larval gallery or very often in a chamber 

 eaten out in the sapwood or in one eaten out in the bast or bark. 



In the case of one Indian polygamous bark-borer {Pityogcncs, p. 562) 

 five or more females are fertilized by the one male beetle, and the five 

 egg-galleries radiate in a stellate manner from the pairing-chamber, each 

 gallery curving inwards, the eggs being laid on the outer side of the curve 

 (cf. fig. 358). 



In all these cases the plans of the egg and larval galleries are constant 

 for the species, and are easily distinguished from each other, as will be seen 

 by comparing the plans made by Polygyaphus (fig. ^^^), Tomicus (pi. liii), 

 and Pityogcncs (fig. 358). In the polygamous forms the egg gallery may or 

 may not be blocked with wood-dust and exxreta by the female beetle. If it is, 



as in the case of Touiiciis, 

 where the gallery is also very 

 long, the beetle eats out one 

 or more aeration holes by 

 boring a horizontal tunnel 

 to the outer bark, lea\'ing a 

 thin lamella of bark on the 

 outside intact. This tunnel 

 serves to let air into the egg- 

 gallery, whilst at the same 

 time the thin lamella of bark 

 covering it prevents preda- 

 ceous foes from getting into 

 the egg-gallery to devour the 

 grubs. When the whole of 

 the eggs are laid the female 

 either dies in the tunnel just 

 above the last-laid eggs, or 

 continues the tunnel for a 

 length of an eighth to a 

 (juarter of an inch and dies 

 in this portion. 



The wood-boring forms 

 of the Scol3tidae oviposit in 

 the wood of the tree, and 

 bore out tunnels which may 

 go straight down into the 

 wood or may enter the tree 



Fk;. 308. — Piece oi Piiins Gcrardiatia bark showing 

 <-'gg-g'iHeries with egg-recesses made by Poly orap/i its 

 trcnchi, Steb. a, pairing-chamber; b, egg-galleries; 

 f, egg-recesses ; d, air-holes ; c, larval galleries. 



