Green aphids include two species that are very difficult to distinguish, the apple aphid, Aphis pomi, and the spirea aphid, A. spiraecola. Recently, the spirea aphid was found to have become the most common species on tree fruits and is thought to have adapted to a host range similar to that of the apple aphid. Hosts of green aphids include apple, pear, quince, and hawthorn trees. The aphids are abundant during June and July on young trees, water sprouts, and vigorously growing terminal branches. They curl the foliage and cover it with honeydew, upon which grows a black fungus that smuts both the fruit and leaves and causes considerable discoloration, especially of early apples.
Eggs are small, shiny, and black. Most are laid on bark or on buds in the fall by the wingless female. The eggs hatch in spring about silver tip. They hatch into stem mothers--wingless females that are pear shaped and bright green. These give birth to a generation of green viviparous aphids, about three-quarters of which develop into winged females. The rest remain wingless. The winged forms spread the species to other parts of the tree or other trees. About half of the second generation and some of the later generations develop wings and migrate.
Unlike rosy apple aphids, green aphids live on the apple tree all year, breeding continuously during the summer. In August and during the autumn months, they are found almost exclusively on water sprouts or terminal branches of young trees that are still growing, and such locations are where the male and female sexual forms are produced.
Immature stages of the green aphids can be distinguished readily from early stages of the rosy apple aphid by the length of the cornicles ("exhaust pipes"). Rosy apple aphids have well-developed cornicles, while those of the green aphids are scarcely developed. Also, the rosy apple aphid has a longer antenna than the green aphids.
Since the overwintering eggs are indistinguishable from rosy apple aphid eggs, early season scouting and management for both species are identical. Since these aphids do not migrate to alternate hosts as rosy apple aphids do, however, they must be scouted for and managed until the terminals harden off. Beginning in early June, randomly select 10 growing shoots (not water sprouts). On each shoot, determine the number of leaves that have aphids. If an average of more than 4.2 leaves per shoot is aphid infested, an insecticide application is recommended. If pesticide applications are necessary, a single spray of product containing imidacloprid will provide excellent control of aphids. Applications of summer horticultural oils will also provide good control of various aphid species. In many years, green aphids will be controlled by naturally occurring predators, including fly and lacewing larvae and ladybird beetles.