Fruit Insect Focus - March, 1998
Rosy Apple Aphid, Dysaphis plantaginea (Passerini)
H. W. Hogmire and S. C. Beavers, West Virginia University
I. Introduction: Rosy apple aphid (RAA) has been a major pest of apple trees in North America since the end of the 19th century. It is the most serious of the five aphid species attacking apple, causing leaf, fruit and systemic root damage. In severe outbreaks, up to 50 percent of the fruit have been injured.
II. Hosts: The primary (overwintering) host of RAA is apple. During early summer, winged females move to the secondary (summer) host, narrowleaf plantain, an introduced weed pest.
III. Description: The egg, which is deposited on the bark of spurs and shoots, is oval and smaller than 1 mm (less than 1/16 inch) long. When first laid it is a bright yellow, but it gradually changes to greenish-yellow, and finally becomes a shiny jet black. The time required for these color changes varies under normal outdoor conditions from about nine days to more than two weeks. Immature aphids that hatch from the eggs in spring are all viviparous (producing live young), wingless females, and when mature are called stem mothers. The body of the immature aphid changes color as it matures, from a dark green immediately after hatching to a more purplish or rosy tinge when full grown (photo 1). Immature aphids possess long cornicles at the base of the abdomen and have long antennae which extend almost half the length of the body (antennae of immature apple grain aphids reach only to the end of the thorax). Winged adults are black and also possess long cornicles and antennae. Summer generations on plantain look distinctly different from the spring aphids on apple. They are a pale yellowish color, and occur singly or in low numbers, rather than in dense colonies. Plantain leaves are not curled by aphid feeding. Males are scarce and are only found in the fall. Oviparae (egg-laying females), also present only in the fall, have a prominent central tubercle on the front of the head, separating this species from green aphids and apple grain aphid. Antennae of RAA have six segments, whereas antennae of apple grain aphid have five segments.
IV. Biology: Egg hatch usually begins when buds are at the silver tip stage in spring and continues over a period of about two weeks, concluding by the half-inch green stage. Immediately after hatching, the young seek out the opening buds of apple (photo 2), seeming to prefer the fruit buds. They feed on the outside of the leaf bud and fruit bud clusters until the leaves begin to unfold, and then work their way down inside the clusters and begin sucking sap from the stems and newly formed fruits. One nymph feeding for 24 hours is sufficient to cause the leaf to be curled when it unfolds. The first stem mothers usually reach maturity when apple trees are coming into pink. They settle down and content themselves with feeding and producing young at a rapid rate. Production of young usually begins two or three days after the last molt and continues without interruption for over a month. A single female produces an average of about 185 young. Normally, the period of reproduction extends from about pink to June 20 or later. The maximum period of productive activity is usually around the last week of May and the first week of June, which is the period when young fruits are beginning to set and start active growth. Populations are usually highest in the inner and upper parts of the canopy. There are approximately three generations produced on apple, with the second generation occurring two to three weeks after petal fall and the third generation appearing by mid to late June. With each succeeding generation of aphids, a larger percentage of alate (winged forms) are produced. By early to mid-July all aphids have developed into alates and have dispersed from apple to summer hosts. About six generations occur on narrowleaf plantain during the summer before winged females fly back to apple in the fall. These females produce wingless oviparae, which mate with returning winged males from the summer hosts. Mated females deposit an average of four to six overwintering eggs, usually in late October and November.
V. Injury: RAA remove plant juices from the leaves, causing severe curling (photo 3) and abscission, and twisting of growing shoots (photo 4). They excrete large quantities of honeydew which provides a substrate for a black sooty fungus which can affect fruit finish. However, the most serious effect results from the translocation of saliva from the leaves to the fruit. This causes the apples to remain small and deformed and renders them unmarketable (photo 5). Systemic effect of the toxic saliva includes reduced growth of roots and other woody tissue. Research at Virginia Polytechnic Institute and State University (VPI&SU) has shown that this can have an important impact on young trees as they develop a mature bearing structure.
VI. Monitoring: Twigs may be examined during the dormant period for overwintering eggs, however, no method exists for distinguishing RAA eggs from those of the other four species of aphids overwintering on apple, or for predicting aphid populations based on egg numbers. RAA can be monitored at the prepink to pink stage of apple development. The sampling should be done early enough to allow the application of an aphicide to the trees before bloom if the threshold is exceeded. Make a three-minute examination of five to ten trees in each orchard (preferably from the cultivars>Rome=, >York=, >Golden Delicious=, or >Stayman=) and count the number of fruit spurs showing curled leaves (photo 2) with live aphids (photo 1). Average the number of fruit spurs across all trees showing evidence of RAA infestation. Repeat the three-minute examination at petal fall. Examine trees during midseason to determine the extent of fruit injury (photo 4).
VII. Management: Research at the Penn State Fruit Research and Extension Center demonstrated that an insecticide application at the green tip to half-inch green stage provided optimum control of RAA. A second application is recommended before bloom if an average of at least one infested leaf cluster per tree is found at the prepink to pink stage of apple development. The presence of this insect after bloom will result in fruit injury. Therefore, an insecticide should be applied at petal fall if any live colonies are found in order to minimize additional injury.
Chemical control - commercial growers
Chemical control - home orchardists
Modified from text prepared by D. G. Pfeiffer, L. A. Hull, D. J. Biddinger and J. C. Killian in the Mid-Atlantic Orchard Monitoring Guide.