The spirea aphid has a broader host range and is more likely to immigrate into apple than apple aphid, which may stay on apple year round or immigrate later in the season. The spirea aphid also tends to be less susceptible to insecticides than the apple aphid. However, these two species are difficult to distinguish and are managed together as green aphids.
Description and life cycle
Overwintering eggs are small, shiny, and black and cannot be distinguished from those of other aphid species. Stem mothers are wingless females that are pear-shaped and bright green. Immature green aphids can readily be distinguished from immature rosy apple aphids by shorter antennae and less well-developed cornicles. In the summer aphids vary from a yellow-green to a light green and have black cornicles.
Eggs are laid on bark or on buds in the fall by the wingless female. They hatch at about silver tip into stem mothers which 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 may develop wings and migrate.
Unlike the rosy apple aphid, green aphids may live on the apple tree all year, breeding continuously during the summer. In August and during the autumn months, these aphids are found almost exclusively on watersprouts or terminal branches of young trees that are still growing, and where male and female sexual forms are produced.
Since the overwintering eggs are indistinguishable from rosy apple aphid eggs, early season scouting and management for both species are identical. However, because this aphid complex does not migrate to alternate hosts as rosy apple aphids do, it must be scouted for and managed until the terminals harden off. Beginning in early June, select 10 growing shoots, not watersprouts, on each of five trees of the major variety within the block. On each shoot, determine the number of leaves that have wingless aphids. If an average of more than 4.2 leaves per shoot are aphid infested, and less than 20 percent of the aphid colonies have predators, an insecticide application is recommended.
A number of natural enemies of aphids have proven effective for biological control of aphids in Mid-Atlantic apple orchards. They include syrphid fly larvae, aphid midge, lacewing larvae, and ladybird beetle adults and larvae. These predators appear as softbodied and sometimes very colorful larvae feeding right in the aphid colonies. A single syrphid larva can clean a leaf of aphids in days. A pesticide application may be delayed or eliminated if 20 percent of the colonies have predators. Use of pesticides with low toxicity to the predators will increase the chance for biological control.
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.