AUGUST
2003

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

08-28-03

Aphids Sometimes Called Plant Lice

Almost anyone who has tried to grow a plant has come into contact with insects known as aphids. Aphids are small insects that average about a tenth of an inch in length. But what these insects lack in size they make up for in numbers, and that is why they become pests.

It was the great numbers of these insects that prompted Erasmus Darwin, grandfather of Charles Darwin, back in the 1700s to describe them as a "prolific tribe." Prolific they are. Aphids are masters of reproduction. One aphid can become thousands in a few weeks.

How does that work? Most populations are made up only of females. These females reproduce parthenogenetically--that is, reproduction without the benefit of mating. Aphid females have cut out the "middle man" in the reproductive process, an approach to procreation that is sure to warm the cockles of radical feminists everywhere!

Eliminating males in the reproductive process saves time. No searching for mates or courtship required. In addition, these mavens of insect reproduction give birth to living young. In a matter of days, these young themselves give birth. It all adds up to a rapid increase in aphid numbers. What ecologists call a population explosion.

Aphids are what some entomologists call sap suckers. These insects use their piercing-sucking mouthparts to remove sap from host plants. The aphid digests some of the sap, but most is eliminated. The waste material is very high in sugar and is known as honeydew.

Because of the sugar content, honeydew is collected by ants as food. That's why ants are frequently found in association with aphids. In fact, the relationship is so common that aphids have been called ants cows. In some instances, ants actually protect the aphids from predators. In the case of corn root aphids, ants carry the aphids to new plants. This activity would be akin to a shepherd moving sheep to a new pasture.

Aphids are very successful in spite of a number of predators and parasites that feed on them. The parasites include tiny wasps called braconids and chalcids. These little wasps go unnoticed by most people because they are so small. However, owners of plants may sometimes find brown aphid carcasses with a round hole in the back. Those are aphids that were consumed by parasites.

Predators also eat aphids. Three of the most common include the ladybugs, the lactwings and larvae of some syrphid flies. Both adult and immature ladybugs eat aphids. The same is true of lacewings. Immature lacewings are such voracious consumers of aphids they are called aphid lions! Syrphid flies are also called hover flies, and, because they are colored like bees, incorrectly called sweat bees by many people.

Aphids are very specific to the type of plant on which they feed. But there are lots of species of aphids, so most plants can have aphids. The aphid names reflect food plants. We have alfalfa aphids, apple aphids, and bean, cabbage, cotton, corn leaf, and green peach aphids. There are also plum and melon aphis and rose and spiraea aphids. There are also aphids with the name walnut, pear, clover, spinach and turnip. Hey, these little insects are everywhere. No wonder some people call them lice.

 

Writer: Tom Turpin
Editor: Olivia Maddox