FAMILY SCOLYTIDAE 



503 



others. In this way the egg-gallery plans 

 shown in figs. A and B are produced. 

 These egg-galleries are bored deep in 

 the bast and sapwood ; they are usually 

 curved and from i in. to iHn. in length. 

 The female, as she bores out her tunnel, 

 gnaws out little notches at the side and 

 places an e^^g, in each. These notches 

 are not made so symmetrically as in the 

 case of the monogamous bark beetle, there 

 being usually more on one side than on 

 the other. From eight to fifteen eggs 

 appear to be laid in each gallery (see 

 fig. A). The first eggs hatch out before 

 the female beetle has finished egg-laying, 

 which process takes from four to six days. 



The larvae, on hatching out, feed 

 almost entirely in the bast and bark, and 

 rarely groove the bast wood. 



They bore winding galleries in a 

 direction approximately at right angles to 

 the egg-gallery, their tunnels averaging 

 three-quarters to one inch in length. 

 These tunnels are closeh' packed with 

 the wood excreta passed out by the 

 larvae in feeding. When full-fed, at 

 the end of about four weeks, they eat out 

 a small chamber in the sapwood (d) at 

 the end of the larval gallery and change 

 to pupae in this. When the pupa has 

 matured into the beetle, in from eight to 

 thirteen days, the latter bores its way out 

 direct to the outside by a horizontal 

 tunnel. Where the bark is of fair thick- 

 ness the portion of the pupal chambers 

 in the wood consists of merely a saucer- 

 shaped depression. It is more usual, 

 however, for the pupal chamber to be 

 entirely hollowed out in the sapwood. 

 From this method of feeding it will be- 

 come apparent that, whilst the whole of 

 the plan of the egg-galleries and larval 

 galleries will be always visible in the 

 bark, it is most usual to find in the sap- 

 wood a central chamber from w'hich three 



=^^ 



"T^. 



_S&S^ 



Fig. 329. — Portion of a young blue 

 pine {Pinus excelsn) sapling showing 

 entrance- and exit-holes of Polvgrapluis 

 tnajo/-, Steb., on outer bark. Jaunsar, 

 North-West Himalaya. 



