This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
If the assertion here made that insects attack unhealthy trees only be true, how wonderfully at fault have been cultivators, who were and are accustomed to consider the insect as the cause of the enfeebled condition of the tree, not the consequence of it 1 Mr. Waterton argues ingeniously in support of his views, and I believe him to be correct to this extent, that insects of any kind prefer attacking a feeble tree to one in vigorous health; but I don't believe that the vigorous trees are never attacked. I am satisfied that the saperda, or apple borer, for instance, does not invariably avoid healthy trees, for I have seen trees in that condition bearing marks of its operations - not many marks, it is true, for if so the tree of course could not continue in a healthy state. Another species of saperda, not many years since, destroyed nearly the whole of the numerous locust-trees in and about this city, as well as in other localities, and they were attacked almost indiscriminately, entire rows of apparently healthy and vigorous trees being utterly ruined, if not killed.
So numerous were the insects that in a still evening their operations were distinctly audible at a little distance from the trees, the sound being like that made by an auger in entering timber, though not, of course, quite as loud. This may seem a rather tough story, but it is literally true. Now the mountain-ash is undergoing a somewhat similar visitation, and of the many fine ones about the city, I fear few will escape. Some of the largest are already nearly destroyed.