WAA.jpgApple Grain Aphid, Rhopalosiphum fitchii (Sanderson)
[= R. insertum (Walker)]

I. Introduction: Apple grain aphid (AGA) rarely causes damage to apple. But since it is generally the first to appear on apple buds in the spring and is often abundant, it often arouses the concern of the grower.

II. Hosts: The primary hosts, on which eggs are placed for the winter, are apple, hawthorn, pear, quince and plum. During the spring and summer, this aphid moves to various grass species.

III. Description: The overwintering eggs are a shiny black, indistinguishable from the other aphids overwintering on apple. Newly hatched nymphs are a dark green color. There is a slightly lighter green area running down the back (Plate 41). The antennae, legs and cornicles are very dark. The antennae are short, reaching about to the end of the thorax. Those of young rosy apple aphid stem mothers reach to about half the length of the abdomen. The cornicles of AGA nymphs are short, barely swollen discs. The young nymphs are generally hard to distinguish without magnification, unfortunate given the great disparity of damage potential between the species. The mature stem mother is 8/100 inch (2-2.15 mm) long. The mature aphids have a darker green stripe along the middle of the back.

The oviparae, or egg-laying females, are a pale, yellow-green, usually with a pale reddish spot at the base of each cornicle. Unfortunately, this description also applies to the oviparae of the other aphids on apple. AGA oviparae possess only five antennal segments; RAA and the GA complex have six segments. Furthermore, RAA oviparae have a prominent central tubercle on the front of the head.

IV. Biology: The eggs of AGA are not killed by periods of warm weather during the winter as are those of AA. These eggs hatch 7-10 days earlier than those of GA and RAA Eggs hatch as buds swell, and young aphids may be found clustered on buds at silver tip. The stem mothers become mature about two weeks after hatch. They begin to produce new nymphs about 24-36 hours after the last molt. Stem mothers produce an average of 75 young, over a period of about 30 days.

Most of the second generation AGA develop wings and leave the apple tree. A few reproduce on the tree. The cornicles are cylindrical, with the base and end slightly constricted but with the end flaring. The dark green stripe is present along the dorsum in this generation as well. The third generation is much less abundant; aphids of this generation develop into winged adults, dispersing to summer hosts.

During the summer, many generations develop on a variety of grasses and cultivated grain crops. In the fall, with the onset of cool weather, winged migrants are produced which return to apple and other primary hosts. Many migrants die through normal fall leaf abscission. The migrants are of two types. The first is the viviparous female, the second is the male, produced for the first and only time during the season, and arriving on the tree about a week after the female migrants. Once migrant females have reached the winter host, wingless, sexual females (oviparae) are produced which produce the overwintering eggs after mating with the males.

V. Injury: Although these aphids may be present in great numbers, damage is rarely inflicted on the apple buds.

This is taken primarily from a chapter by D.G. Pfeiffer, L.A. Hull, D.J. Biddinger, & J.C. Killian on apple indirect pests, reprinted with permission from Mid-Atlantic Orchard Monitoring Guide, published by NRAES, 152 Riley-Robb Hall, Ithaca, New York 14853-5701.

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