there was a general migration or scattering of this species thruout the orchards and numerous rapidly growing colonies were established on the tender terminal growth. The colonies of rosy aphis, which, up to this time, had, on the whole, been quite free from other forms, now began to be mixed with the green aphides. As this species increased in numbers the rosy aphis decreased, so that by the end of July the green aphis was quite abundant and was the only one of the three forms remaining on the apple; this condition continuing thruout the rest of the season. The oat aphis.-This was the first species to appear on the apple buds at Geneva, and, owing to the late spring, hatching did not occur until April 22 or nearly a week later than the record of the preceding season. At the time of the first appearance of the nymphs most of the buds had barely begun to show green at the tips. A very few were slightly more advanced, while many of the more backward still showed no signs of life whatever. Within four or five days after the nymphs first appeared, all of the eggs had apparently hatched, and altho infestation was quite general no case of extremely heavy infestation was observed, the numbers of aphides on infested buds varying from one to fifteen in most cases, and probably averaging four or five. The stem-mothers of this species matured just as the blossom buds were beginning to show pink, the first being observed producing young on May 10, and at this time the leaves were well out and the fruit buds were fairly well separated in the clusters. As reproduction progressed the numbers of these aphides greatly increased, and the fruit clusters became literally coated with the insects. Strangely enough, there was little apparent effect on the tissues as the result of the feeding of these colonies of insects; at most, there was only a gentle curling of the heavily infested foliage. The second generation of this season consisted entirely of winged forms, which began leaving the apple as the petals were dropping, and from this time until the middle of June the numbers of this species on apple decreased rapidly. By the time the fruit had reached the size of marbles the aphides had entirely disappeared. The rosy aphis.— The earliest nymphs of this species were observed coincidentally with those of the oat aphis, but the hatching of this species was prolonged over a somewhat greater period than that of the latter form, and young nymphs continued to appear as late as April 29. As soon as the young emerge from the eggs they migrate to the opening buds, and, like the other common species, creep down among the tender new leaves as they unfold. There is, however, apparently a more decided tendency with this species to remain with the leaves which they first attack, and not to advance to the tips of the more succulent growing shoots of the leaf clusters as seems to be characteristic of the other species. The attacks of this species result in a severe and characteristic curling of the leaves, which was first observed shortly before the maturing of the stemmothers, and which became common with the maturing of these insects; a single stem-mother was sufficient to curl a leaf tightly. About the time the fruit buds had turned pink the stem-mothers began to give birth to the nymphs of the second generation. These nymphs showed little inclination to migrate and, as a rule, remained within the curled leaf occupied by the stem-mother until the leaf became overcrowded with the developing aphides. During the latter part of May and early June many new colonies were formed by these nymphs that were thus crowded out of the original colonies and forced to migrate to the tender foliage. The period of the dropping of the petals was marked by a great increase in the numbers of this species, due to the maturing of the second generation. Few, if any, of these developed wings. With the development of the third generation, however, the winged forms appeared, and by the middle of June the migrants were observed producing nymphs on plantains. After this period the numbers on apple began to diminish and after July first the decrease was rapid, due to the increasing activities of the natural enemies as well as to the flight of the winged forms. By the latter part of July the apple was entirely free of the insects. The green apple aphis.- The hatching of this species at Geneva began on April 26 and was completed by May 2. The stem-mothers began to mature on May 13, as the blossoms were showing pink, and the infestation grew more severe. By far the greater part of the second generation was composed of winged forms, and during the last of May and the first few days of June there was a definite migration flight from the densely infested colonies to the uninfested parts of the orchards. Altho winged forms were produced thruout the rest of the summer, they were never sufficiently numerous to cause a definite, general migration. The effect of species on the foliage is intermediate between that of the other two species. During the early spring, curling of the leaves was not greatly in evidence except in cases of very severe infestation. As the summer broods became abundant, however, curling of the leaves became characteristic of the infested orchards. INFLUENCE OF APHIDES ON FRUIT. In order to ascertain more definitely the nature and extent of injuries sustained by apple fruits as a result of attacks by the different species of aphides, some studies were carried on along lines somewhat similar to the efforts of the summer of 1915. For this work a Rome apple tree was selected which was practically free from infestation by these insects and as far as external conditions indicated, was representative of this variety in this orchard. At intervals during the spring varying numbers of aphides were placed upon apparently normal fruit clusters. After this operation each of these artificially infested clusters was immediately enclosed in a very thin, black, silk-netting bag, which was allowed to remain until the insects left the fruits or until the end of the growing season in case of A. pomi. The fruit clusters may be grouped in four series, viz.: Series I, artificially infested with A. sorbi; Series II, infested with A. avenæ; Series III, infested with A. pomi; and Series IV, checks, which were free of aphides and covered with bags similar to those of the foregoing series. Because of the fact that the fruit clusters were enclosed in cloth bags, it was considered necessary to pollinize the flowers artificially. On May 23 the blossoms were found to be in an ideal condition for fertilization; and so the bags were removed from the clusters and pollen was placed upon the pistils by stroking the flowers with others taken from adjoining trees. The bags were at once replaced in their former positions. At frequent intervals during the summer the condition of the fruit clusters with respect to the activities of the insects was noted and the fruits were measured. The principal details of the experimental activities with the different series are briefly summarized, viz., Series I. In this series are included twenty-two fruit clusters which were artificially infested with sorbi, as follows: One cluster with five stem-mothers on May 8. One cluster with eight stem-mothers, May 15. Three clusters, each with one stem-mother, May 16. Three clusters, each with one stem-mother, May 19. Five clusters, each with one wingless female of the second generation, June 13. Two clusters, each with one colony, June 22. The fruits of this series were calibrated on June 27; July 5, 19, 29; Aug. 7, 11, 18, 25, and September 1, 7, 16 and 30. The records are shown in Table I and are summarized in Table V. Series II. This series includes nine clusters which were artificially infested with avena as follows: One cluster with fifteen stem-mothers, May 9. Five clusters, each with thirty stem-mothers, May 13. Measurements of the fruits were taken on June 27; July 5, 19, 29; August 7, 11, 18 and September 1, 7, 16 and 30. The records are compiled and summarized in Tables II and VI. Series III. Includes seven clusters artificially infested with pomi as follows: Six clusters, each with from forty to sixty stem-mothers, May 19. These clusters were examined and the fruits measured on June 27, July 5, 19, 29; August 11, 18 and September 1, 7, 16 and 30. The measurements are given in Table III and are summarized in Table VII. Series IV, checks. The ten clusters in this series were enclosed in the netting bags exactly as those of the other series, but no aphides were admitted. Two of the clusters were bagged on May 8 and the other eight clusters on May 12. Observations and measurements were made on June 27, July 5, 19, 29, August 11, 18 and September 1, 7, 16, 30. Table IV shows the measurements, which are also summarized in Table VIII. |