Green Peach Aphid (GPA)

Myzus persicae

Written by: 

Jaime Pinero

Overview

GPA adults and nymphs do the damage in three ways: first, they feed directly on young tender plant tissues, often drying out shoots, causing wilts and distortions; second, they produce honeydew which falls onto foliage and becomes blackened by sooty mold fungi; and third, they spread many types of viruses. Plants injured by GPA feeding will have leaves that appear curled, distorted and discolored. 

The GPA mainly attacks peach; however, apricot, plum, cherry, and a wide variety of vegetable and floricultural crops can be attached by GPA.

Eggs – oval, shiny black; about half the size of a pencil point. The eggs are only found on the bark of fruit trees.

Nymphs – Green peach aphid nymphs resemble wingless adults in color (have black legs and antennae) but are smaller.

Adults – Wingless forms are light green to yellow. Winged forms are pale to dark green with a large dusky blotch on the abdomen. The body of the winged form is much slimmer with large oval shaped clear wings. The rear of the green peach aphid has 3 extrusions of the body wall called cornicles.

Biology

GPA has a complicated life cycle. Within a single growing season, GPA populations will have multiple asexual generations. GPA overwinters as an egg on the bark of fruit trees, specifically peach, cherry, apricot, and plum.

Egg hatch occurs on fruit trees about the time of peach bloom. GPA has both a sexual and asexual form. The majority of reproduction occurs asexually by a process called pathogenesis, where live young (females only) are produced by unmated females, called stem mothers.

Development occurs very quickly, growing from neonate to adult in as few as 5 days. At some point during the summer, winged adults develop which disperse to alternate hosts including many vegetable crops. Generations developing on vegetable crops will have both winged and wingless adults and reproduce asexually. In late August winged forms will migrate back to fruit trees.

Near the end of the growing season on fruit trees, sexual forms of the green peach aphid appear for the first time. After mating the female green peach aphid will oviposit eggs on the bark of fruit trees. GPA may have 10+ generations in a growing season.

Monitoring

Beginning at petal fall, inspect the undersides of leaves for new colonies. For faster inspection, shake limbs over a cloth tray (“beating tray”) to observe the dislodged insects.

It is important to identify parasitized aphids, which result in mummies. The presence of mummies (see picture of parasitized GPA) indicates that parasitic wasps are actively attacking aphids.

Economic threshold: Treat peaches when there are two or more colonies per tree before shuck split, or six or more colonies per tree after shuck split. 

Management

Aphid population levels are heavily influenced by temperature, rainfall, numbers of natural enemies present and frequency/type of pesticide application. Aphid outbreaks are most frequent in hot dry weather. Heavy rains will often reduce the aphid population below the economic threshold.

Aphid predators and parasites usually keep populations low. The most common are lady beetles (adults and larvae), syrphid fly larvae, green lacewing larvae, and tiny parasitic wasps that lay their eggs in the aphids. The wasp larvae develop in the aphids eating the inside parts and turning the aphids into empty shells called "mummies". There are many parasitoids attacking the green peach aphid with, perhaps, species of Aphidius and Aphelinus, the most important. 

When pesticides are applied care should be taken to select pesticides that are not damaging to natural enemies of aphids. Because aphids reproductive rate is greater than their natural enemies, incorrect pesticide use may contribute to aphid outbreaks by removing the natural enemies.