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.