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Ants and Aphids: Someone to watch over me...
by Brenda Landers-Smith

This article was an ARS Award of Merit winner for 2005.

I get by with a little help from my friends... John Lennon, 1967

ant tending aphids
Ant tending aphids

You may not be aware of a friendship that has developed among your roses in the garden. It began with an innocent introduction. But after the "how do you do's" and casual conversation, something more intimate has developed. This is not a story of romance, of chivalry and valor, but a dynamic chemistry between two high profile characters you meet year after year. Unfortunately, they are also your rose's enemy... Allow me to introduce the aphid and the ant.

Aphids (Homoptera), also known as "plant lice" are one of the most common plant pest insects. They are pear shaped, soft bodied insects often only 1/8-inch in length with long legs and antennae. They have long, thin mouth-parts that resemble beaks, which they spear into plants and suck the juices (sap) from the plant tissue. Some species of aphids are also responsible for spreading many different viral diseases. Aphids come in almost every color from green, yellow, pink, brown, black, and any shade in between. Take a look under a magnifier to confirm the diagnosis. An aphid will have a tiny pair of cornicles that have been described as looking like "dual exhaust pipes" on their posterior. Aphids are the only insects that have them!

rose pest: aphid

Aphids live in colonies and are usually found on tender, developing buds and undersides. They over-winter as eggs and show up in Southern California around the month of March as adults ready to feast. You may ask, "Why so many and so fast?"

The life-cycle of aphids is attributed to the fact that female aphids reproduce parthenogenically (without males). The females emerge from over-wintering eggs as "stem mothers;" they do not need a mate to reproduce. They then give birth to live daughters that in turn give birth to live granddaughters. The fast growing population is the result of rapidly producing females. Aphids reach adulthood in one week. Later in the season they produce both sons and daughters... then finally mating occurs and eggs are laid to "over winter" to begin the cycle again.

The attractive feature that brings ants into the romance is honeydew. Yes, honeydew, the sweet nectar of the aphid. With this attraction, the ants become the knights in shining armor to aphids. In a survival of the fittest world, of enemy combatants such as spiders, ladybugs, lacewings, and minute parasitoids, the aphid has an ally: the ant. Aphid honeydew secreted from the cornicles is a sugary liquid waste that ants LOVE. While ants are tending and protecting their friends to ensure their supply of this nectar, ants use their legs to rub the aphids which stimulates them to produce the honeydew. This activity is known as "milking" the aphids.

Honeydew in itself poses an unsightly problem. The honeydew secreted from aphids sometimes falls like a fine rain on leaves below. A black fungus is then colonized, called "sooty mold." Although the leaves are not directly hurt by the droplets, the sooty mold shades necessary sunlight.

Ants will also fend off aphid predators and rescue aphids by carrying them to safer territories. A less romantic way to describe this rescue is the ants "farm" the aphids like a Lilliputian cattle herd and protect them from harm. (They also have an affinity for cottony scales, mealy-bugs, soft-type scales, and white flies.) Ants also save aphid eggs in their nests over the winter and bring them out in the spring. Indeed a friendship of devotion and dedication.

But alas, our roses do not like the sap sucking aphid nor the co-conspirator ant - so what can you do to keep them out of your rose garden?

Understanding the dynamics of these partners-in-crime may help observant rosarians combat the problems they cause. Funny, even in the world of insects the saying "I'll scratch your back, if you scratch mine" applies.

Images from Wikipedia.

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