Young aphids congregate closely around the stem mother. This habit soon causes the death of the infested leaves and the consequent migration of the aphids. Photo by G. Krawczyk.
While apple trees are its preferred host, this species also feeds on pear and hawthorn trees.
Description and life cycle
The body of this aphid has a waxy coating and usually a slight purplish or rosy tinge; hence the name. Eggs are laid on the bark of apple trees, are oval, and about 3/100 inch long. When first laid they are a bright yellow that gradually changes to greenish yellow and finally within two weeks to shiny jet black.
Egg hatch and feeding
Egg hatch occurs between silver tip and ½-inch green. The young, as soon as they hatch, seek out the opening buds of the apple, 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. Then they work their way down inside the clusters and begin sucking the sap from the stems and newly formed fruits. Their feeding causes the leaves to curl, affording the aphids protection from insecticide applications and some natural enemies.
The first young develop into stem mothers when apple trees are coming into pink stage. The production of young usually begins 2 or 3 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 May 10 to June 20 or later. The maximum period of productive activity often coincides with the period when young fruits are beginning to set and grow actively.
Young aphids congregate closely around the stem mother. In some cases, the congregations are made up of more than one layer of aphids. This habit soon causes the death of the infested leaves and the consequent migration of the aphids. When several stem mothers congregate on a single leaf, forced migration soon follows. The young move actively to locate a suitable feeding ground. It is at this period that they are frequently found congregated on the forming fruits or attacking the new succulent unfolding foliage.
Nymphs of the second generation, all of which are females, reach maturity in 2 to 3 weeks; the great majority begin to reproduce on the apple, although a few may develop wings and migrate to the weed plantain. The third generation is produced in June and early July. The majority of this generation develop wings and migrate to plantain. In some seasons wingless females of the third generation produce a fourth generation on the apples. In the fall, the winged females fly back to the apple trees. They are darker than the migrants that left the tree in spring. These returning females lay eggs, from which males also develop. The males mate with the females, which then deposit eggs on the bark.
These aphids cause a decrease in tree vigor because of foliage loss and damage to the fruit through dwarfing, misshaping, and staining. The severe curling of foliage caused by this species is probably the most characteristic feature of its work. A single stem mother located on the underside of a leaf near the midrib will cause the leaf to fold almost as tightly as the outer wrappings of a cigar. The presence of only a few stem mothers can cause a severe curling of all leaves surrounding an opening flower bud; within such curls ideal protection is afforded to the rapidly developing aphids. A cool, wet spring favors aphid development because it provides conditions unfavorable for parasites and predators of aphids.
Starting at early pink, 5 to 10 trees should be selected from each block. Sensitive varieties such as Rome, York Imperial, Golden, and Stayman should be selected if present. For 3 minutes, on each tree, count the number of fruit spurs showing curled leaves. If more than one aphid-infested cluster is observed per tree justifies an insecticide treatment to prevent fruit injury.
Maintain properly trimmed trees to make conditions less favorable to aphids and to achieve better spray coverage.
Optimum timing for control of rosy apple aphid is at green tip to half-inch green. Specific chemical recommendations for home gardeners are in Fruit Production for the Home Gardener, and recommendations for commercial growers are in the Penn State Tree Fruit Production Guide.