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As a result of their activities various distortions of apples developed. Severe infestation by A. sorbi and A. pomi was attended in a number of instances by destruction of entire clusters of apples.
In an experiment on Rome apples an application on May 1 of lime-sulphur and nicotine sulphate at recommended strengths afforded efficient protection from the oat aphis and the rosy aphis. The trees receiving the treatment were also free from the green aphis until June, when there was a re-infestation of the plat due to invasion by winged migrants.
Of twelve auxiliary experiments, nine gave appreciable benefits from spraying. The remainder were inconclusive because of slight infestation by the insects or excessive defoliation by apple scab assisted in part by. aphides.
As losses by aphides vary according to locality and seasonal conditions, the experiences of orchardists are the best criteria of the necessity of systematic spraying to combat the insects. To obtain positive evidence of the destructive influences of aphides on the apple crop and the effectiveness of spraying, growers should conduct a test, for which directions are given. The results of such an experiment continued for a period of years ought to indicate the practicability of undertaking larger operations as a regular procedure in the upkeep of apple plantings.
In continuance of the plan previously outlined in Bulletin 415 of this Station, various studies on the life histories and habits of several species of apple aphides and experiments to develop more efficient spraying practices were repeated during the past season. important results and applications from these efforts are considered under the following captions:
1. Classification of newly-hatched larvæ and stem-mothers of first brood.
2. Seasonal behavior of aphides.
CLASSIFICATION OF NEWLY-HATCHED LARVÆ AND
STEM-MOTHERS OF FIRST BROOD.
The newly-hatched nymphs of the three common apple aphides are tiny insects closely similar in appearance and in habits. All are usually of a dark green color, and it is only by close examination that the several species may be distinguished. While the adults are much more easily separated, it is frequently important that the species be determined at the very beginning of the season, before maturity is reached. These stages of the different species may be distinguished by the accompanying descriptions.
IDENTIFICATION OF NEWLY-HATCHED NYMPHS.
Aphis sorbi Kalt. is of a very dark green color, in the first stage, with a pair of darker areas on the head and several rows of dark tuberculate spots extending lengthwise of the body. The antennæ, legs and cornicles or“ honey-tubes” are dark in color. The antennæ are long and slender, reaching nearly to the bases of the cornicles, which are long and prominent, somewhat en
C larged distally and flanged at the tip. The entire insect is more or less covered with whitish powder, giving it a rather bluish appearance, which, together with the longer antenna
Fig. 7.-ANTENNÆ AND CORNICLES: A, pomi; B, sorbi; C, avence. and cornicles, at once distinguishes this species from both pomi and avenæ. (Plate XXX, fig. 2, and Fig. 7, b.)
Aphis pomi DeGeer is usually of a dark green color, a trifle lighter than the corresponding stages of sorbi and avence, varying, however, to almost a lemon yellow. The head is dusky and rather brownish. The antennæ are intermediate in length between those of the other
species under consideration, and are dusky in color, especially toward the apex. Legs darkened on the distal ends of the segments. Cornicles dark colored and conical in shape. The distinguishing features of this species are the moderate length of the antennæ, and the conical "honey tubes," which are shorter than those of sorbi, yet considerably longer than those of avenæ. Sometimes the body is somewhat powdery but not so much so as in the case of sorbi. (Plate XXX, fig. 1 and Fig. 7, a.)
Aphis avence Fab. is of even darker hue than either of the other species. There are two large blackish rectangles on the head, while the antennæ and legs are very dark in color, and the cornicles are black. The antennæ are shorter than those of either of the other species, reaching to the middle pair of legs, while the cornicles are extremely short, being mere discs. The short antennæ and abbreviated cornicles form ready means of distinction for this species. (Plate XXX, fig. 3 and Fig. 7, c.)
IDENTIFICATION OF MATURE STEM-MOTHERS.
Aphis sorbi Kalt.-- As this species approaches maturity there is a gradual but considerable change in appearance, and the adult is no longer green but of a variable and almost indescribable tint. Usually this is a dark bluish slate color, and more or less powdery. Some specimens are paler, the color varying to a rather yellowish brown. The antennæ are slender, usually reach about to the middle of the abdomen and are black in color except on the basal portion. Cornicles long, somewhat curved, and black in color. Besides the coloration, which easily separates this species from the others, a further means of identification is the fact that the stem-mothers will usually be found securely hidden within a tightly curled leaf.
Aphis pomi DeGeer undergoes a less decided modification in coloration as maturity is reached, the adults being a bright green color. The head is usually tinged with brownish and varies to blackish; the rest of the body is bright green, varying in some individuals to a lemon yellow. Antennæ are relatively about as long as those of the preceding species, and together with the legs are of a rather dusky brownish color. The cornicles and cauda are very dark brown or black, in striking contrast with the bright green abdomen.
Aphis avence Fab.— This species becomes much lighter in color as growth continues. By the time the insects are half grown they are pale green in color with more or less distinct darker green markings on the body. The adult is pale yellowish green with a series of transverse spots, which together form a broad, deeply serrated band extending the full length of the abdomen. The antennæ and cornicles are relatively somewhat shorter than those of either of the other species. The species is not likely to be confused with sorbi because of the difference in coloration, and may be readily distinguished from pomi by the dark green markings present in the latter species.
SEASONAL BEHAVIOR OF APHIDES INJURIOUS TO APPLE
FOLIAGE AND FRUIT.
At the beginning of the season, aphis infestation in apple orchards was not severe in western New York during 1916. At the outset, the oat aphis by far outnumbered the green aphis or the rosy aphis in most of the orchards. The relative abundance of the three species varied, however, under local conditions, and in some of the Experiment Station orchards the rosy aphis actually presented a greater number of colonies early in the season than both of the other forms combined. In this case, however, even the rosy aphis infestation was not severe.
It is interesting to note that the relative abundance of the three species passed through a seasonal succession or cycle, which, while probably varying somewhat from year to year, must remain fundamentally constant. Activities began with the hatching of the oat aphis, which was first observed at Geneva on April 22. On this date considerable numbers of this species were present on the apple buds, and the very young nymphs continued to appear for several days. Simultaneously, a few nymphs of the rosy aphis were found in company with the oat aphides, but it was not until four days after the first observation that they reached their maximum abundance. The green aphis was the last to appear, the first nymphs emerging from the eggs on April 26. Three days later, while there were still a few unhatched eggs, the great majority of the nymphs had emerged and were feeding on the green buds. It was observed that there was a characteristic difference in the distribution of the eggs of the green aphis as compared with those of the other two species. That is, the eggs of the green aphis, while not occurring in numbers thru
out the orchards generally, were localized, and occasional twigs could be found which were heavily infested with the eggs. On the other hand, the eggs of the oat aphis and the rosy aphis were uniformly scattered thru most of the orchards observed and, while infestation was more severe in the case of isolated and uncared-for trees, there was apparently much less tendency for the eggs to be aggregated in small, dense colonies. As would be supposed, this had considerable effect on the relative local abundance, and distribution of the several species during the early part of the season. The immediate result of this difference in egg distribution was that the oat aphis nymphs, the most common species, were to be found thruout the orchards, and there was a sprinkling of the rosy aphis nymphs in company with this species, while the green aphis was very largely limited to local colonies in which infestation was very
The oat aphis was the first to mature, and the rapid reproduction of this species soon greatly increased its relative abundance so that it became by far the most numerous species. Two days after the maturing of the stem-mothers of the oat aphis, the rosy aphis began to give birth to living young, and, while the rate of reproduction was fully equal to that of the former species, the initial abundance of the oat aphis kept the latter ahead in point of numbers. The green aphis was one day behind the rosy aphis in maturing, and the offspring served to increase the severity of the local centers of infestation. The second generation of the oat aphis was composed entirely of winged migrants, which began to leave the trees during the latter part of May, or at a time when the fruit had reached the size of marbles. By the middle of June this species had become greatly reduced in numbers and by the end of the month it had entirely disappeared from the apple. While the oat aphis was becoming less abundant because of migration to the summer food plants, reproduction by the second generation of the rosy aphis greatly increased the numbers of this species which was rapidly superseding the oat aphis, so that during the interval extending from about the middle to the last of June the rosy aphis was the more abundant of the two species in the orchards about Geneva. After July first migration of the rosy aphis was rapid and the numbers diminished until the latter part of the month, when the apple had been entirely vacated. The second generation of the green aphis was to a very large extent composed of winged forms, and during the last of May