SOME INSECTS INJURING-NUT TREES.
By W. E. Britton, State Entomologist, Connecticut.
Nut-bearing trees, like other kinds of trees, are attacked by insect pests. Some kinds are seriously injured by them; others scarcely at all. Some of these insects are borers in the trunk and branches; some devour the leaves; some feed inside the nuts and ruin them; some suck the sap from the stems and leaves.
I shall make no attempt in this paper to enumerate these pests. Time forbids. I shall only mention a few of the most obvious and most serious, and where possible, point out control measures.
The Walnut Caterpillar.
Datana integerrima G. & R.
During the month of August clusters of blackish caterpillars bearing white hairs, may be seen stripping the terminal branches of black walnut, butternut and hickory trees. This is called the walnut caterpillar, and it has been very abundant in Connecticut this season. Many small trees have been entirely stripped and large ones almost defoliated. There is only one brood each year in Connecticut, though two occur in the southern states, and the pupae winter in the ground. The adult is a reddish brown moth, having a wing-spread of about one and one-half inches. Clipping off the twigs and crushing the mass of caterpillars is perhaps the simplest control method on small trees. Spraying with lead arsenate will prevent defoliation.
The Fall Web-worm.
Hyphantria cunea Drury.
Though a general feeder attacking all kinds of fruit, shade and forest trees, the fall web-worm commonly feeds upon the foliage of nut trees, especially hickories, causing considerable damage in the South. The adult is a white moth, having a wing-spread of an inch or more, appearing in midsummer and laying its egg-cluster on the under side of a leaf. The young caterpillars make a nest at the end of a lateral branch by drawing the leaves together with their webs. These nests usually appear in July and August, though in Connecticut there is a partial second brood and usually a few nests of the early brood may be found in June. In the South there are two complete generations. When the larvae have exhausted their food supply, they extend their nest by taking in fresh leaves, but always feed inside the nest, differing in this respect from the tent caterpillar which makes its nests here in May. When fully grown the caterpillars are about one and one-fourth inches long, with brown bodies covered with light brown hairs, and may be seen crawling about seeking a place to pupate. They soon go into the ground where they transform, the adults emerging the following year.
The best remedies are (1) clipping off and burning the nests when small, and (2) spraying the foliage with arsenical poison.
The Walnut Bud Moth.
Acrobasis caryae Grote?
Inconspicuous nests containing small caterpillars are often found at the ends of the new shoots of Juglans regia, seriously injuring them, and sometimes killing the trees. One small tree two feet high was killed, and thirty-five pupae were found in the nests at Dr. Morris' farm in 1912. The adult is a small gray moth with a wing expanse of about three-fourths of an inch. There are three broods each season in Connecticut, the larvae appearing about June 1, July 10 and August 18.
By spraying the foliage with lead arsenate (3 lbs. in 50 gals. water) this insect can be controlled. One application should be made about June 1, followed by a second about July 10.
Though this insect is thought to be Acrobasis caryae Grote, it is often difficult to distinguish some of these species in this genus without a knowledge of their food habits and seasonal life histories. We possess such knowledge regarding this species which we have studied and reared in Connecticut, but it is lacking in connection with adult specimens in the United States National Museum labeled caryae, which superficially seemed identical with ours. Further study, therefore, may prove this to be an undescribed species. There are other bud-worms attacking nut trees, especially in the southern states, where they cause considerable damage to pecans.
The Walnut Weevil Or Curculio.
Conotrachelus juglandis LeC.
Probably the most serious enemy of Juglans, in Connecticut at least, is the walnut weevil or curculio, Conotrachelus juglandis LeC. The larvae tunnel in the tender shoots, often ruining the new growth, and they also infest the nuts. The adults feed upon the shoots and leaf petioles. Observations on the different hosts indicate that Juglans cordiformis and J. sieboldiana are preferred, and the most severely injured, followed in order by cinerea, regia, nigra and mandshurica.
Though described as early as 1876, little was known about the life history of this insect until the studies were made at the Station in 1912 by Mr. Kirk and the writer. Formerly it was supposed that this insect attacked and injured only the nuts or fruit, and Dr. Morris in 1909 seems to be the first on record to observe the injury to the shoots of Juglans regia. It was on the trees of Dr. Morris here in Stamford and those of Mr. H. L. Champlain at Lyme that the life history studies were made. There is but one brood each year, and the winter is passed in the adult stage. The beetles appear the latter part of May and feed upon the stems and leaf veins during the egg-laying period, which extends from the last week in May up to August 1st. The eggs are laid in irregular crescent-shaped punctures, similar to those of the plum curculio, and hatch in from six to twelve days, depending upon the weather.
From four to six weeks are necessary for the development of the larvae, and when mature they go into the ground where they remain for about ten days an inch or so beneath the surface. They then pupate, and from sixteen to twenty days later the adult beetles emerge. They fly to the trees and eat small holes chiefly at the base of the leaf petioles, but must early go into winter quarters as they are seldom seen after the first week in September.
This insect occurs throughout the Eastern United States, but seems to cause more injury in Connecticut than has been noted elsewhere. The remedy is to spray the new shoots and under side of the leaves about June 1, with lead arsenate (6 lbs. of the paste in 50 gallons of water), to kill the beetles when feeding on the leaf petioles.
The Nut Weevils.
Balaninus sp.
Several kinds of nuts are attacked and injured by long-beaked snout beetles or weevils belonging to the genus Balaninus, the chestnut probably being the most seriously damaged. All of them feed inside the nuts or fruit during the larval stage, and the larvae are without legs. As both the methods of attack and the life history are similar for all species, they will be considered here in a group. For the sake of distinguishing them, however, their names are mentioned.
Larger Chestnut weevil, Balaninus proboscideus Fabr.
Lesser Chestnut weevil, B. rectus Say.
Hickory nut or Pecan weevil, B. caryae Horn.
Hazelnut weevil, B. obtusus Blanch.
Common acorn weevil, B. quercus Horn.
Mottled acorn weevil, B. nasicus Say.
Straight-snouted acorn weevil, B. orthorhynchus Chittn.
Sooty acorn weevil, B. baculi Chittn.
Confused acorn weevil, B. confusor Ham.
Spotted acorn weevil, B. pardalus Chittn.
All of these weevils pass the winter in the ground in the larval stage, transforming to pupae about three weeks before the adult beetles emerge, which varies from June, when they are usually few and scattering, to September, when they have become abundant. Thus there is a single brood each year, and the larval period lasts from three to five weeks in the nuts and some ten months in the ground, from two to eight inches below the surface.
The control of these weevils is difficult, and ordinary methods such as spraying are not effective. In fact little can be done other than destroying the weeviled nuts, which may be fed to hogs. When first gathered the nuts may be fumigated with carbon disulphide. About two fluid ounces of the liquid should be used for each bushel of nuts and placed in a shallow dish on top of the nuts, which should be enclosed in a tight box or barrel. The period of fumigation should be from 12 to 24 hours. Where nuts are not to be used for seed they may be thrown into boiling water for about five minutes—just long enough to kill the weevils. The nuts are then dried and sold. Most of the weeviled nuts will rise to the surface and may be discarded, but this test is not absolute and cannot be depended on to distinguish the sound from the weeviled nuts.
Hickory Bark Beetle or Bark Borer.
Scolytus quadrispinosus Say.
Outbreaks of the hickory bark borer occur periodically throughout the northeastern United States, and during the past five years many hickory trees in this vicinity have died.
The adult is a small black beetle appearing in May and June, which eats holes in the axils of the leaf stems causing them to fall early—usually in July and August. Brood galleries are then made longitudinally just under the bark of the trunk by the female, and a row of eggs is placed along either side of this brood chamber. On hatching the grubs, which are at first very small, tunnel at right angles to the central chamber, each making its own separate gallery. These galleries never meet or cross each other, but must necessarily diverge toward their extremities as they become larger. The effect of this is to girdle the tree which soon dies. The larvae pass the winter under the bark, finish their development in the spring, pupate, and the adults emerge in May and June from small round holes about the size of bird shot.
For control measures, Dr. Hopkins advises examining the trees during the fall and marking all dead and dying trees within an area of several square miles. Then between October 1 and May 1, cut all such trees and dispose of the infested portion to destroy the insects before the adults emerge.
Many forms of treatment have been devised and recommended by tree doctors for the control of this insect. Some of them may be worth trying; most are of doubtful value, and some are absolutely injurious to the trees. On July 3, 1914, some affected hickory trees on the Station grounds were sprayed heavily with powdered lead arsenate, 4 lbs. in 50 gallons of water, to which one pint of "Black Leaf No. 40" was added. Two days later many dead beetles were found on the tar walks under the trees, and a few were observed each day up until about the middle of August. Most of the trees treated, however, had been so badly injured by the insect that they were removed. Since then this insect has caused little damage on the grounds, though a few hickory trees still remain. In 1901 an outbreak of the hickory bark beetle caused the death of 110 trees on the Hillhouse place in New Haven; then the destructive work of the insect ceased and the few remaining hickory trees are still standing and in fairly good condition. I mention these instances to show that nature's control methods through parasites and natural enemies is far more effective with certain pests than any which man has yet devised. Of course, we hope that in the future man will make better progress along this line.
The Painted Hickory Borer.
Cyllene pictus Drury.
There are several borers attacking the wood of the trunk of the hickory, but one of the commonest is the painted hickory borer. It also occasionally attacks black walnut, butternut, mulberry and osage orange. In hickory especially the larval tunnels are often found in the wood when trees are felled. There is probably one brood annually and the winter passed in the pupa stage, though it may possibly hibernate as a larva. Its life history is not fully understood. It is a common occurrence in Connecticut, and specimens are sent me every year, for the adult beetles to emerge in March from firewood in the house or cellar and crawl about seeking a chance to escape. The housewife fears that a terrible household pest has descended upon her, and with fear and trembling invokes the aid of the Agricultural Station.
The beetles appear outside in April and May, and probably oviposit soon afterward. They are about three-fourths of an inch in length and are black, prettily marked with golden yellow.
The insect can be controlled only by the old arduous methods of digging out, and injecting carbon disulphide into the burrows.
Several other long-horned beetles are borers in the hickory and other nut trees. Then, too, the leopard moth, zeuzera pyrina Linn., and the carpenter worm, Prionoxystus robiniae Peck, may be found occasionally in most any kind of tree.
The chestnut tree (if it has thus far escaped the blight or bark disease) may show small, deep tunnels into the wood of trunk and branch, made by the chestnut timber worm, Lymexylon sericeum Harr. Slow-growing woodland trees are more apt to show these galleries than trees of rapid growth standing in the open.
There are a number of tussock moths, sawflies, beetles, etc., which feed on the leaves of nut trees. Spraying with lead arsenate will prevent damage. There are also many sucking insects attacking them, such as the hickory gall aphis, and several species found on the leaves. Some of these may be controlled by spraying with a contact insecticide such as nicotine solution or kerosene emulsion.
In the Southern States, pecan trees are attached by some of these insects which I have mentioned; there are also many more which cannot even be mentioned in the time allotted to this paper. Information may be obtained regarding them, by any one interested, and for this purpose I have appended a short list of publications.
Literature.
Britton, W. E., and Kirk, H. B. The Life History of the Walnut Weevil or Curculio. Report Conn. Agr. Expt. Station for 1912, page 240.
Brooks, Fred E. Snout Beetles That Injure Nuts. Bull. 128, West Virginia Agr. Expt. Sta., Morgantown, W. Va., 1910.
Chittenden, F. H. The Nut Weevils, Circular 99, Bureau of Entomology, U. S. Dept. of Agr., Washington, D. C., 1908.
Felt, E. P. Insects Affecting Park and Woodland Trees. Memoir No. 8, N. Y. State Museum, Albany, N. Y. 2 vols., 1905, 1906.
Gossard, H. A. Insects of the Pecan, Bull. 79, Fla. Agr. Expt. Station, Gainesville, Fla., 1905.
Herrick, G. W. Insects Injurious to Pecans, Bull. 86, Miss. Agr. Expt. Station, Agricultural College, Miss., 1904.
Hopkins, A. D. The Dying Hickory Trees. Circular 144, Bureau of Entomology, U. S. Dept. of Agr., Washington, D. C., 1912.
Kirk, H. B. The Walnut Bud Moth. Report Conn. Agr. Expt. Station for 1912, page 253.
A Member: Early in the spring I noticed something on the hickory trees swollen and bright red in color, so that the trees were conspicuous from a distance. Later insects emerged which appeared to be these little gnats that fly in swarms.
Dr. Britton: From the description I am not able to say what it was, but it was probably one of those gall flies, a great many species of which exist and which attack all kinds of plants. They do not, as a rule, cause very serious damage, and I can not suggest any particular remedy. Did it interfere with the growth of the tree?
A Member: I noticed what seemed to be the same insect on the grape vines.
Dr. Morris: I would call attention to one pest that is very destructive to hazels; unless watched closely it will produce serious injury. That is the larvae of two of the sawflies. Dr. Britton was unable to determine off-hand the species of the specimens I sent him, but you may know the sawfly larvae by their habit of collecting in a row like soldiers around the edge of the leaf and when the branch is disturbed, their heads and tails stand up. These sawfly larvae need looking after and can be killed by spraying. They usually collect on two or three leaves at a time.
I would like to ask about a bud worm that attacks the leaf of the hickory near the axil, sometimes very extensively, but not very injuriously. At the same time it makes deformities. Colonies of this insect select certain trees, for instance, the Taylor tree that you saw yesterday is infected with this particular bud larva. The base of a petiole becomes enlarged two or three times, and you will find one white worm at the bottom. This colony is confined to this one tree, and the very next tree adjoining the Taylor has its branches interwining, but is not bothered at all, so far as I can determine.
This colony habit is also true of the hickory nut weevil—the hickory weevil makes the Taylor tree a colony house, whereas I haven't found a single weevil in nuts of the adjoining hickory tree that has its branches interwining.
That colony habit is, perhaps, a weak point with the weevil, and it may enable us to eradicate them by concentrating our attention upon their colony trees.
One point in regard to the chestnut weevil. When our chestnuts began to die here, I supposed that the chestnut weevils would immediately turn to my chinquapins for comfort. Weevils attack the chinquapins so extensively in the South that Mr. Littlepage said chinquapins would not be acceptable to Dr. Kellogg because they furnished so much animal diet. (Laughter). Curiously enough, the chestnut weevils did not go to my chinquapins. These chinquapins bear full crops, heavy crops, and one will almost never find a chestnut weevil in the nuts. I have found now and then a little weevil, about half a dozen altogether, that attacks the involucre at its point of attachment to the chinquapin. This looks like the chestnut weevil, but perhaps, only according to my eye, very much as all Chinamen look alike to one who has never seen them before.
The matter of carbon disulphide for the painted hickory borer. I have used that apparently successfully, but I didn't tunnel through six feet of hickory tree afterward to see whether the borers were dead or not. It is a successful treatment for apple borers. I have no trouble with the apple borers now. I simply clean off the entrance of the hole, the "sawdust," and then with a little putty spread out with my hand make a sort of putty shelf below the hole, then I squirt in a few drops of carbon disulphide with a syringe, turn up the putty and leave it adhering to the bark, closing the hole. You can do that very quickly, and it spares a good deal of perspiring and backache.
The black walnut. On one of my black walnut trees there is a serious pest, a very little worm which infests the involucre. The black walnuts of this tree fall early. I found that same worm last year also extending to the Asiatic walnuts, so that a great many Japanese walnuts fell early as the black walnuts fall, as a result of this little worm's working in large numbers within the involucre. I sent some specimens to New Haven for the species to be observed. This will be a very serious matter if it is going to involve the English walnuts as it does on Long Island. I have found the same thing, apparently, on Long Island in the black walnut, in the English walnut, and in the pecan. It causes a serious drop of these nuts at Dana's Island, near Glen Cove, Long Island.