FAMILY SCOLYTIDAE 513 



but do not reach quite to the outside, a plate of cortical epidermis 

 of paper-like thickness being left to cover the hole (d). Two or more 

 aeration holes of this nature are made, and they serve to admit air into 

 the egg- and future larval-galleries. These holes are not carried right 

 through to the outside, in order to prevent predaceous and parasitic enemies 

 from gaining access to the inside and destroying the grubs, pupae, or 

 beetles within. These air-holes appear to be bored in an erratic manner. 

 At times the egg-gallery will contain three or more right at its commence- 

 ment, and their number and position doubtless depend to a great extent 

 on the healthiness of the tree and the amount of resin it is capable of 

 exuding at the spots attacked. If this is in such quantities that the 

 entrance-hole of the male and female beetles becomes blocked, the females 

 doubtless have to add considerably to the number of the air-holes in their 

 egg-galleries. This may also in part be responsible for the number of 

 female beetles who enter and pair with a male. The number is evidently 

 very variable, at any rate in the case of the spring and early summer 

 generations. There are always two, but there may be as many as four. 

 The second female beetle entering by the entrance-hole, after pairing 

 with the male, carries her egg-gallery in the opposite direction to that 

 of the first. If the latter has gone up the tree she will go down, and vice 

 versa. These egg-galleries, at any rate in their lower halves, are always 

 packed with the wood-dust eaten out by the beetle as she carries the tunnel 

 onward, and this probably prevents a second female from commencing her 

 gallery in the same spot. If a third beetle pairs with the male she carries 

 her gallery either up or down the trunk, parallel to, but not in connection 

 with, that of the female which has previously taken this direction. If there 

 are four females, two egg-galleries will be found proceeding up the tree 

 and two down, each taking off from the pairing-chamber. I have never 

 found more than four females with one male. At times as many as three 

 beetles will be found in the pairing-chamber, perhaps a short egg-gallery 

 having been started at one or both ends. In this case it is possible that the 

 female beetles help the male to enlarge the pairing-chamber. The galleries 

 vary in length from if in. to 2^ in., the number of eggs laid in each being 

 from fourteen to eighteen. Probably about a week to ten days is spent 

 in making the egg-gallery, and the lower eggs hatch out into grubs before 

 the beetle has finished boring the gallery and ovipositing (fig. 308, c). Only 

 a day or two is spent in the egg stage. The grubs on hatching tunnel 

 away from the egg-gallery in a direction which is more or less at right 

 angles to it in the case of those first hatching, and therefore the lowest eggs, 

 the direction, however, trending upwards (or downwards when the egg- 

 gallery is carried downwards) in the case of the eggs laid higher up the 

 gallery. In this manner a pattern which has a constant definite plan 

 is made. The larval galleries are short, not being more than iin. to 

 i k in. in length, and they groove both bark and sapwood. When full- 

 grown the larva eats out in the sapwood an oval -shaped depression, and 



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