Rosy Apple Aphid
The rosy apple aphid, Dysaphis plantaginea, has been a major pest of apple trees, causing both direct and indirect injury since the end of the nineteenth century. The egg, laid on the bark of apple trees, is oval and about 1/2 millimeter long. When first laid, it is bright yellow, but it gradually changes to greenish yellow and finally to a shiny jet black. The individuals that hatch from the eggs in spring are all viviparous (giving live birth) wingless females, which are called "stem mothers" when mature. The bodies of these aphids have a waxy coating and usually a slight purplish or rosy tinge, hence the name.
There are five instars, the last being that of the mature stem mother, which begins to parthenogenetically (without mating) bring forth living young shortly after the fourth instar. These young are produced at an average of five to six per day. The nymphs of the second generation, all of which are females, reach maturity in 2 to 3 weeks; the great majority begins to reproduce on the apple, although a few might develop wings and migrate to the weed plantain. The third generation is produced in June and early July. The majority of this generation develops wings and migrates to another plant species--plantain.
Although apple trees are its preferred host, this species also feeds on pear and hawthorn trees. Untrimmed trees make conditions more favorable for aphids and greatly handicap methods of control. A cool, wet spring favors aphid development because it provides conditions unfavorable for parasites and predators of aphids.
The eggs usually hatch when buds are at the silver tip stage in spring. Egg hatch is complete by the 1/2-inch green stage. 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 sprays and some natural enemies.
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. Another of this species' most characteristic features is the congregating of young aphids around the mother. Each stem mother or group of mothers will have hundreds of young massed about it so that infested leaves might soon be covered--in some cases, by more than one layer of aphids. This habit of congregating soon causes the death of the infested leaves and the consequent migration of the aphids.
In the fall, the winged females fly back to the apple trees. The males mate with the females, which then deposit eggs on the bark. Overwintering eggs are usually present sometime before silver tip. If eggs are found, delayed-dormant oil and insecticide sprays should be applied. Starting at early pink, trees should be routinely inspected. Pay particular attention to sensitive varieties such as Golden Delicious, Rome Beauty, Stayman, and York. For 3 minutes, count the number of fruit spurs showing curled leaves on each tree. If, on average, more than three-quarters of the clusters are aphid infested, a pink insecticide application of a product containing imidacloprid is recommended.