By Fred E. Brooks

Associate Entomologist U. S. Department of Agriculture

The prevalence of insect pests need not be regarded as an alarming obstacle to nut growing in the North, and yet there are numerous species of insects which are capable of destroying our nut crops. On the whole I presume there are fewer insects that attack nuts in this country than commonly attack apples, but apple growers are not limited in planting nor prevented from making profits on account of insect depredations. Neither should the probability of more or less insect injury discourage the would-be planter of nut trees.

The presence of an insect in any locality may mean, among other considerations, that the soil, and climatic conditions of that locality are favorable to the plant upon which the insect feeds. We may be sure that wherever the Baltimore butterfly is abundant, nearby is a congenial spot where the turtle's-head, the food plant of the butterfly, flourishes. Just so, in localities where there are many chestnut weevils we may expect to find chestnut trees thriving and fruiting generously. The same is true of the associations of many other insects and plants.

Theoretically speaking, one would not care to risk the expenditure of much time or money in propagating a plant in a region that was destitute of insects that might attack that plant. The absence of such insects would possibly indicate a lack of natural conditions favoring the growth of the plant in question. Thus the presence in any locality of insects that feed on nuts may mean that nuts thrive naturally in that locality and that insects are there because of the abundance of a favorite food.

May I hasten to add, however, that this fact should not lead to an under-estimation of the possibilities of insect destructiveness, nor encourage lax methods in dealing with injurious species. In the beginning of any nut-growing enterprise we should anticipate the coming of insect pests and be ready to meet them. The planting of pure stands of native nut trees sets up a condition under which insects coming from the forest may increase more safely and rapidly than under the more hazardous environment of a scattered forest growth. This applies to cultivated plants generally. It is true of an orange grove, a cornfield or a potato patch. The mass planting of any crop is quite sure to call sooner or later for measures to offset the stimulus which such plantings offer to insect increase.

Reference may be made to a familiar nut plantation which illustrates a natural result of neglecting one of the insect factors. This plantation is the government's chestnut orchard at Bell, Maryland, which was planted for scientific purpose some years ago by Dr. Van Fleet. This orchard of around one thousand trees contains numerous species and varieties of chestnut, some of which bear fruit every year. The various scientific projects carried on in this orchard in the past have all been of such a nature that they called for no consideration of weevil increase. Many nuts have been allowed to lie under the trees until the weevil larvae issued and entered the soil. This has resulted in a constant increase of weevils until infestation of the nuts became practically one-hundred per cent. All nuts of the crop of 1922 were so wormy that when planted they failed to germinate. Injury to the crop of 1923 seemed somewhat less severe, but its extent may be indicated by the fact that 3080 nuts from this orchard which were kept by the speaker in rearing jars yielded 11,085 worms. In the woods adjacent to the orchard the native chestnut trees are disappearing on account of the blight, and presumably weevils are on the decrease. Within the small area of the orchard, however, the increase has been abnormal, due, as has been indicated, to the peculiarly favorable and man-made conditions. If, from the time the trees of the orchard began to bear, the investigations being carried on had called for close gathering of the nuts at maturity and the destruction of all the worms that issued from them, there is little doubt that infestation would have been kept within reasonable bounds. At present, after two years of attention to the collection of ripening nuts, there is an apparent decrease in the number of weevils. Strong emphasis should be placed upon the importance of gathering chestnuts as soon as they are ripe and prevention of the worms from reaching the soil. This is especially true of districts where woods surrounding chestnut orchards do not contain bearing native chestnut trees.

The Nut Weevils

Now that the subject of nut weevils has been introduced, let us consider in more detail these grotesque, long-snouted insects whose larvae, or grubs, play havoc with so many of our nuts. Most of us have had the experience of gathering in autumn rich stores of our delicious native chestnuts. But how often our anticipations of boiled and roasted feasts have been blighted. We have found that the chestnuts were like the manna which fed the children of Israel in the wilderness, "When we left of them until the morning they bred worms and became foul." There are numerous cases in this country where chestnuts in shipment have been seized and condemned under the provisions of the Food and Drugs Act. Usually the phraseology of the libel has been "because the shipment consisted in part of filthy animal substances, to wit, worms, worm excreta, worm-eaten chestnuts and decayed chestnuts." Altogether the loss to chestnuts from weevil injury is beyond computation.

The beetles which are the parents of the familiar worms in chestnuts are not commonly seen, or, if observed, they are not associated with the disgusting inhabitants of the nut kernels. These beetles represent in their structure a very interesting adaptation to a special end. The mouth is located at the tip of an enormously long snout, or proboscis, and the drill-like instrument is used for puncturing the thick covering of various kinds of nuts so as to admit the egg into the kernel upon which the young will feed. In some cases the mouth is situated at a greater distance from the eyes and other head appendages than is the anal extremity of the insect. There are in the northern part of this country two species which attack chestnuts, one which attacks hickory-nuts, one which attacks hazel-nuts and about a dozen which attack acorns. And here may be mentioned an interesting peculiarity of the feeding habit which is decidedly to the advantage of the nut-grower. Each species adheres closely to its own food plant. The hickory-nut weevil does not attack hazel-nuts nor the hazel-nut weevil hickory-nuts. None of the acorn-infesting species will seek for food in the nuts of chestnut, hickory or hazel. Once the chestnut weevils are absent in a locality, there is no chance that oak trees will serve as a means of spreading the weevils back into the locality. So closely confined are these weevils to their particular food plants that many of them distinguish between the different species of oak and will oviposit only in certain kinds of acorns.

All the different species resemble one another in both the adult and larval stages. There is also a general similarity in their behavior. I have recently discovered, however, a marked difference in the life cycles of certain species. For example, the larger chestnut weevil and the smaller chestnut weevil look alike, but they are decidedly unlike in their development. The grubs of the larger weevil begin to leave the nuts at about the time the nuts drop. They enter the soil to a depth of several inches and fashion smooth-walled cells in which they remain unchanged until the following summer. During June and July they transform to pupae, and soon afterward to adults. In August they issue from the ground and seek the trees where they collect around the burs and begin to deposit eggs soon after the nut kernels start to form. This life cycle is continued year after year. To forestall starvation of the race in case of entire failure for a year of the chestnut crop, a few individuals carry over the second winter in the ground and then issue as beetles along with the one-year-old specimens. It is probable that a small per cent of the insects may remain in the soil over three winters. Thus does nature by unique arrangements safeguard the lives of even the very small creatures.

The life cycle of the lesser weevil is quite different. The larvae of this species leave the nuts somewhat later in the autumn than do those of the larger weevil. Like them, they enter the ground and pass the first winter unchanged. The grub stage is continued throughout the summer, but late in autumn, after the beetles of the larger species have been on the trees for some weeks and deposited most of their eggs, the larvae of the smaller species transform to adults. Instead of coming from the ground, however, they remain in their earthen cells throughout the winter. The next spring, prior to the blooming of the chestnut-trees, they emerge from the ground and soon thereafter collect in large numbers on the male catkins of the chestnuts. At this time very little feeding is done and the sex instinct does not manifest itself. As the time approaches for the nuts to mature, however, the beetles begin to feed and pair and soon thereafter to lay their eggs in the ripening nuts. Most of the eggs are deposited directly into the nuts after the burs begin to open. In the case of the larger weevils the beetles are present only about three months of the year. Those of the lesser species, however, are perpetually present, those of the younger generation reaching the adult stage in the ground before those of the previous generation have finished laying their eggs in the ripening nuts. As with the larger species, a few of the smaller weevils carry as larvae for several years to tide over possible failures of the chestnut crop. The life cycle of the hickory-nut weevil is similar to that of the larger chestnut-weevil, and that of the hazel-nut weevil is like that of the lesser chestnut weevil. Both cycles are represented among the acorn-infesting species.

Any intelligent warfare against the nut weevils calls for a knowledge of these distinctive life histories. Thus, an abundance of maturing larvae of the larger species this autumn will insure an abundance of beetles to deposit eggs in the nuts next autumn. With the lesser weevil, however, maturing larvae this autumn will not affect the number of beetles on the trees the succeeding autumn but will provide beetles for the crop two years hence. Large numbers of beetles of the lesser species may be destroyed by collecting them from the blossoms of chestnut, but, at that season of the year there are no beetles of the larger species abroad.

These weevils are to be made the subject of a bulletin by the Bureau of Entomology in the near future, in which it is hoped to go more fully into a discussion of control measures.

Walnut Husk Maggot

Although none of the weevils of the group just discussed attacks walnuts, the fruit of this tree has a serious enemy in the walnut husk maggot. This insect is most familiar in the form of multitudes of dirty-white maggots inhabiting the blackened, slimy husk of ripening walnuts. Originally, the black walnut furnished the favorite food of this insect, although the husk of butternuts was sometimes attacked. More recently the pest has turned its attention to the Persian walnuts which are fruiting in many places in the east. The watery, dark-colored pulp into which the husk of the nut is converted when the maggots begin to feed penetrates the shell of the nut and injures the kernel by staining it and imparting a strong flavor. The operation of hulling is also made doubly disagreeable, the nut coming out of the husk discolored and dirty.

These maggots hatch from eggs inserted into the husk of nuts by a light-colored fly about the size of our common housefly. Although easily overlooked, these flies may be seen on the nuts at almost any time in August and September. They have strong ovipositors with which they puncture the surface of nuts and insert into the openings masses of white eggs from which the maggots hatch.

As to the control of this pest, the speaker obtained very promising results in spraying Persian walnut trees belonging to our friend, J. G. Rush, at West Willow, Pa., with a solution of 1-1/2 pounds of lead arsenate to 50 gallons of water with 10 pounds of glucose sugar added to impart a sweet taste. The flies were observed feeding on the sweet coating given to the leaves and the nuts that ripened later were comparatively free from maggots. It was obvious that the flies died from the poison before depositing many eggs in the nuts.

Twig Girdlers

During the past two seasons the speaker has made special studies of several species of beetles which cut or girdle young hickory trees, or the branches of larger trees, causing the severed part to break off or die. Not fewer than four distinct species of beetles in the east have this habit. Three of the insects do their damage in the larval stage. One of these, Elaphidion villosum, has been called the twig-pruner. It is a well known species and its work in pruning the branches of hickory and various other trees has often been referred to. The other two species which sever the wood in their larval stage are Pseudobidion unicolor and Agrilus arcuatus. Thus far, these two have no common names. In certain localities they are proving to be very troublesome to both young and bearing trees. In one block of a nursery in Virginia I estimated that the Agrilus larvae had ruined one-hundred dollars worth of young hickory trees. Fortunately, the adult of this species feeds freely on hickory foliage and can be killed readily under nursery conditions by spraying with arsenical poisons.

The fourth girdler referred to is our familiar hickory twig-girdler, Oncideres cingulatus. In this case the adult insect cuts a ring-like furrow around the wood and the portion above dies. The purpose of the girdle is to provide dead wood in which the young may feed. After the girdle is made, a process which occupies several hours, and, sometimes several days, the eggs are laid in the bark above. In central West Virginia and northward the grubs which hatch from these eggs require two years in which to reach maturity. In the vicinity of Richmond and southward, however, the larvae mature in one year. This more rapid development in the south probably accounts in part for the recent serious outbreak of this insect in Virginia and the Carolinas.

Each female beetle is capable of girdling several twigs. One female of about a dozen kept in confinement last autumn made eleven girdles and deposited 55 eggs. Several of the beetles continued their interesting operations until after several snows and severe frosts had occurred.

The twig girdler in the beetle stage feeds rather freely on the bark of twigs. Enough of the surface is eaten to justify the belief that the beetles may be killed by spraying with arsenical poisons. This treatment is being tested at the present time. In the cases of all these insects which sever the branches the wood is killed for the safety and comfort of the insect as it undergoes further development above the severed point. There is a period of at least several weeks in each case after the twig dies during which the insect in one stage or another remains in it to complete its growth. This affords an opportunity to gather the twigs and burn them with the assurance that the insects are being destroyed thereby.

At least some progress has been made in discovering the habits and the methods of controlling these and various other insects that may be expected to give nut growers in the north more or less trouble. The remedies that can be offered at the present time are not in all cases entirely satisfactory. There is much yet to be learned, but there are control measures within the reach of most of the nut growers which are well worth consideration and adoption.

THE SECRETARY: Dr. Zimmerman, will you read to us now?

DR. ZIMMERMAN: Perhaps some of the members will not be so glad to hear what I have to say, but I feel that there is a need for something along the line I will refer to.