Collectively the hickories have no considerable number of destructive insect enemies, but if we count all the species of the various orders that have been found occasionally, or otherwise, feeding on the leaves, buds, fruit, twigs, bark, or boring in the solid wood, they make a very formidable list of names, or about one hundred and seventy-five in all; but fully ninety per cent. of these depredators are scarcely known, except to a few professional entomologists, and unless they become more destructive in the future than they are at present, or have been in years past, nut culturists have little to fear from their depredations. Among the most common species of insects injurious to the hickory, the following may prove most annoying to the cultivator.
The hickory-twig girdler (Oncideres cingulatus. Say).—A small yellowish-gray beetle, a little less than an inch long, usually appearing in this latitude during August, the females depositing their eggs in the twigs of from a quarter to a half-inch in diameter. On old large trees the loss of a few or many of these is scarcely noticed; but on young seedlings or grafted stock it is quite a different affair, for on such plants the females usually select the leader in preference to the lateral twigs in which to deposit their eggs. The female girdles the twigs for the purpose of providing proper and acceptable food for her progeny; that is, first the green, then the slowly drying, then the perfectly hard, seasoned hickory or whatever kind she may have attacked. Selecting a suitable twig, she rests upon it, usually with head downward (Fig. 70), and with her mandibles cuts out a ring of bark about one-twelfth of an inch wide, and deep enough to reach the firm wood underneath. The place selected for this annular incision may be only a few inches from the terminal bud, or a foot below it, and in some instances she will cut two incisions on the same twig some distance apart, but usually there is only one on a twig. While cutting this incision she will sometimes rest long enough from her labors to deposit an egg in the bark above. The number of eggs she deposits in the twig is probably variable, but three full-grown grubs is the most I have ever found, and the larger proportion examined had only one. This girdling of the twig prevents the flow of sap, and the leaves soon wither and drop off, and the bark and wood shrivel and become hard and dry; but in the meantime the eggs have hatched and the minute grubs have bored their way through the soft bark and reached the pith, feeding in this while acquiring size and strength of jaws that will enable them to consume more solid food later and during the succeeding winter, spring and summer. Some do not reach maturity until the second summer; at least, in this latitude, as I have found after very careful observation and while collecting many hundreds of specimens. I will say, however, that this insect is usually referred to by entomologists as rather rare, and in general it is, but some years ago, in an old clearing near by where there was a great number of young hickory seedlings and sprouts, it was for a season or two very abundant; then it suddenly disappeared, and I have not taken a half-dozen specimens since. The grubs bore out the wood in the infested twig, and in most instances so completely as to leave only a thin shell of the wood or bark, by the time they have reached maturity and are ready to pass into their imago or perfect-winged stage.
This species of twig girdler also attacks the apple, pear, persimmon, elm, and other kinds of trees, and with those like the apple, with a soft and brittle wood, the girdled twigs are frequently broken off by the winds; but this rarely occurs with the hickories, and we can usually find the stumps remaining on the trees years after the beetles have emerged. The only way to keep this pest in check is to cut off and burn the girdled twigs any time before the larvæ have reached maturity, and as the girdled dead twigs are readily seen, the gathering is not difficult, from medium-sized trees.
The painted hickory borer (Cyllene pictus. Drury).—This is, perhaps, one of the most common and widely distributed of all the hickory borers, but, so far as my observations have extended, it rarely attacks young or healthy trees of any age; in fact, I have never found it in or about growing trees, but I have seen it, by the thousands, breeding in decaying specimens and in hickory cordwood cut during the winter months and ranked up in shady places. A hickory tree cut down in fall or winter, and left on the ground or cut up into cordwood, is pretty sure to attract this borer early in spring, the females swarming over the bark, depositing their eggs upon it, and by the ensuing autumn the wood will be fairly honeycombed if this insect is at all abundant. The general color of the beetle is black, and the size as shown in Fig. 71. There are three narrow, whitish bands across the top of the thorax, and one slightly broader band at the extreme point of the wing-covers; but the next band is in the form of an inverted V; the point of the Λ does not quite touch the broad lateral band, as in the closely allied species known as the locust borer (C. robiniæ), with which it is often confounded; besides, in the latter the markings are of a deep yellow, and not white or of a faint yellowish tinge. The hickory borer always appears in spring, and the locust borer in the fall, not later than September in this part of the country. Below or behind the V-shaped band there are three others, but all broken up into mere dots, and not continuous.
[FIG. 71]. HICKORY BORER.
In the South, and especially in Texas, there is a somewhat smaller but closely allied species (Cyllene crinicornis) that attacks the pecan tree and its wood in the same way as our common hickory borer, but in the Southern or Southwestern species the bands on the wing-covers are all interrupted or broken up into small white spots or dots. I have no remedy to suggest, further than to cut down old, infested trees, and to haul the wood out into the sun and spread it out where it will quickly dry and become seasoned. If the felled tree and wood is stripped of its bark as soon as cut, the female beetles will not deposit their eggs upon it.