The Amazing Life Cycle of the Aphid

Author: Dale Odorizzi, Master Gardeners of Lanark County

Like every gardener I know, my garden has been visited – or should I say, attacked– by aphids. In my earlier gardening years, I sprayed and squished trying to eliminate every one. Then twenty years ago, I joined Master Gardeners and in one of my courses learned about the absolutely amazing life cycle of the aphid.

Aphid eggs and parthenogenesis

Aphids overwinter in our gardens as eggs. In spring, the eggs hatch as asexual females—no males are needed. Within five days, these females start producing roughly five nymphs every day for 30 days, until they die. All spring and summer, these asexual females produce live offspring without the necessity of fertilization. This is called parthenogenesis. They have many generations throughout the summer. The mother gives birth to her live young (known as viviparity) right where she happens to be sitting. This isn’t because she is such a good mother. It is just that she is lazy and does not have wings to fly to another plant.

From time to time, the plant gets overcrowded, and the next batch produces asexual females with wings. The winged females then fly to other plants to continue the process. Sometimes, they will fly to the same type of plant they were born on and other times, to something completely different. In autumn, aphids realize that winter is coming, and it is time to produce sexual males and females. This generation breeds and produces eggs that will then overwinter.

Live an Aphid Life!

Aphids spend most of their lives with their straw-like beaks stuck into leaves and stems, sucking out sweet plant juices, causing stunting, leaf yellowing, or leaf distortion if severe. They secrete honeydew, leading to sticky residue and sooty mould on the fruit and foliage. They act as a primary vector of several economically significant virus diseases, spreading the virus as they feed. Ants have a good relationship with aphids. They harvest the sweet sticky sap, and they help to protect the aphids from their many predators.

Required for our Ecosystem – an Important Food Source

Most gardeners jump into action at the sight of an aphid on their prized plants but they actually are an important part of our ecosystem. The larvae of many insect predators love to eat aphids — lady bugs, lace wings, hover flies. Earwigs are voracious eaters of aphids. Parasitic wasps lay their eggs in aphids.

My favourite aphid predators are birds. A chickadee can eat up to 1500 aphids in an hour. They feed them to their nestlings as an important protein source. I always thought of hummingbirds as simply nectar eaters but in fact, their nestlings require protein to develop, and the hummingbirds find that in the form of aphids.

Do I bother Removing Aphids? Generally, No.

I am quite a “laid-back gardener,” to quote Larry Hodgson. I rarely do anything to remove aphids from my plants unless I see significant damage. I have a large stand of Heliopsis (false sunflower) that is frequently covered in bright red aphids. The plant doesn’t seem to mind, so neither do I. I like to leave the aphids for the birds and the beneficial insects.

But sometimes I do.

If you do not like to see them on your plant, there are a few ways to get rid of them. A hard spray of water will often dislodge them. Failing that, spraying with insecticidal soap is effective. Remember, though, that the soap must contact the insects to kill them, so you will have to keep checking the plants regularly to get rid of them. Please do not use any of the home-made recipes that abound on many gardening sites, as many are not effective and can cause harm to your plant and to other insects in the vicinity.

My favourite approach is to simply start at the bottom of the stem and run my fingers up it, squishing the aphids as I go. I usually do not have a hose or a bottle of spray with me when I am looking at my garden, and this is a quick, easy, and satisfying solution.