I have very carefully examined your beetle and find that it is _Hylesinus crenatus_, sometimes known as the “Large Ash-bark beetle” to distinguish it from _Hylesinus fraxini_, the “Ash-bark” or the “Small Ash-bark beetle.” The life history of each kind is stated to be the same, and I think, if I remember rightly, that some time ago, perhaps a year or so, in the course of our occasional correspondence, we have gone into the history of the _fraxini_, but if not I should have pleasure in either looking up the account in my Manual and sending the pages to you or condensing the points.
There appears to me to be this difference in method of larval proceedings: that whereas in the case of _fraxini_ the parent galleries are formed somewhat in the shape of a T with a short stem and long arms to the top, and the larval galleries placed at right angles to the others (fig. 36), so far as I understand this form is not followed by _crenatus_ fig. 38).
The beetle obviously pierces the bark, for the orifice is visible; and in or under the bark there are the mother-galleries, but I do not find the larval galleries feathering as it were from these, and the figure before me gives the idea of the body of larvæ having by their united attack cleared a flat space from which they have continued their solitary tunnels. Perhaps in cutting up your trees you may come on some of these markings. It is said that there are two generations in the year, of which the flight time of one is in April and of the other in October. This species frequents oak as well as ash, which is an important consideration, and I find it noted as frequenting old trees. These are the main points which I see about the history. I should think that if you find the trees which you have felled much infested, it would be a good thing to strip the bark off and burn it.
1, Beetle, with wings expanded, and one wing-case drawn only in outline, to show lower part of wing; 2, beetle as usually seen—magnified; 3, smaller and paler variety; also lines showing natural length.
FIG. 37.—GREATER ASH-BARK BEETLE, _HYLESINUS CRENATUS_, FAB. ]
FIG. 38.—PIECE OF ASH-BARK, SHOWING MOTHER GALLERIES OF _HYLESINUS CRENATUS_ ON THE INNER SIDE. ]
I am very much obliged to you for all the great trouble which you have been good enough to take about the Ash-bark beetles, including your letter of the 23rd and the box of specimens received to-day. Some of the workings are quite certainly of _H. fraxini_. One bit catches the eye at a glance as showing quite typical galleries. In the long strip the workings are not so clearly distinguishable. According to descriptions or comparison with other specimens they appear to me of both kinds. But I really cannot think of giving you further trouble. We have all that is needed to make out a good, sound account, and I hope, if all be well, to do justice to the subject in my next Annual Report, and that you will be satisfied with my working up of the points of the infestation.