Species of this group are apt to have alternating periods of increase and decrease and a year of great abundance may be followed by a year of comparative scarcity. This variation is due, at least in part, to the fact that the larvae, as they feed within the tissues of their host plants, often become rather heavily parasitized by certain two-winged and four-winged flies, the parasitized larvae dying before they reach the adult stage. Nature in this way does considerable toward holding the pests in check, but artificial means of control will often need to be considered.
The third group referred to is represented by a two-winged fly, about the size of the common house fly, known technically as Rhagoletis suavis, and commonly as the walnut husk-maggot. The fly is light brown in color, with broad, irregular, dark brown bands on the wings. It appears when walnuts are nearly grown and deposits clusters of small, white eggs within punctures in the husks. Maggots hatch from the eggs and at the time the walnuts drop these maggots are often found converting the inner parts of the husk into a blackened, pulpy mass. Infested nuts are disagreeable to handle and the husk does not part readily from the shell. I have found the fly attacking black walnuts, butternuts, Persian walnuts and Japanese walnuts, within the states of West Virginia, Maryland, Pennsylvania, Ohio, New York, Connecticut and Massachusetts. It probably occurs over the natural range of the black walnut and butternut. It is proving to be a rather serious pest, especially of the Persian walnut. Some of the infested walnuts appear to drop prematurely and others adhere to the branches beyond the regular harvest time. The shell of infested Persian walnuts parts poorly from the husk and the nut is discolored, soiled and unmarketable.
The fly has rather interesting habits. I found that by pricking a nearly mature black walnut with a pin, the wounds would almost invariably be used in a little while by the female flies for depositing their eggs. In one such wound, 180 eggs were laid within 24 hours. When the husk was pricked a slight flow of juice would take place and the male flies would soon find the spot, and, recognizing, I suppose, a suitable place for the females to come to oviposit, they would stand guard at the puncture awaiting the coming of the female. On one occasion I made minute punctures in the husk of eight black walnuts and in a little while a male fly was located at each puncture. Pairing took place usually as soon as the female came and began to lay eggs. Sometimes a male would be found at a puncture in the early morning and would hold its position against all coming males throughout the entire day. When another male would come to the nut the two flies would rear up facing each other and engage in a brief sparring bout with their front legs. Usually, the original occupant of the nut would be the victor. In some experimental spraying of Persian walnut trees in Maryland and Pennsylvania the past season with a sweetened arsenate of lead spray apparently good results were obtained. In one case it seemed that the spraying was about 75 per cent efficient in controlling the pest. In in another case, whereas last year 75 nuts in 100 were infested, this year, after spraying only four nuts in 100 contained the maggots at harvest time.
I desire to state to the nut growers that I am interested in any nut insect problems that you may encounter and shall always be glad to receive reports and specimens. Your co-operation in this work is greatly appreciated and I hope we may continue to work together and that before long we may have more definite knowledge of the means of preventing, to some extent at least, the various forms of injury by insects to the nut crop.
Mr. Rush: I cannot help but express a word of gratitude and appreciation to my friend Mr. Brooks in helping me out of a serious difficulty that I had in connection with walnut culture at Lancaster. A year ago I was ready to throw up the sponge. In fact I might say that my whole crop last year was destroyed by this husk-maggot. This year I have a very fine crop. Last year it was practically worthless. This year I have very few walnuts that were affected by the maggots, largely owing to the successful spraying that he gave the trees at the proper time. I think the future has a bright prospect for making walnut culture more profitable.
The President: We are certainly under obligations for the very interesting talk and glad that Mr. Brooks could be with us.
The first thing on the program for the afternoon session, according to the published program, I know will be of a most interesting character, Top-Working Hickories, by Robert T. Morris.