MAY
1998

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

05-14-98

Aphids Are Part of Rites of Spring

Spring in temperate regions means renewal of life. Perennial plants bud and leaf. Migratory birds return and build nests. Aphids show up!

Yes, aphids. Some of the most common, although often unnoticed, insects are aphids. Indeed, the ditty that begins: "Spring has sprung, the grass is riz” could very well be completed with the words "and that is where the aphids is!”

The feeding habit of aphids can best be described as sap sucker. Aphids helping themselves to the sap sometimes reduce the vigor of the plant. You'll hear no terms of endearment here from gardeners or farmers. In fact, many species of aphids are important plant pests.

The pest status of aphids sometimes is due to more than merely stealing sap. These insects also are important vectors of the viruses that cause mosaic, stunt and dwarf diseases of plants.

In addition, the presence of aphids sometimes causes plant leaves to curl. This, of course, is unacceptable to the gardener trying to produce a perfect plant.

All of the plant sap that these suckers suck is processed through the digestive tract of the insect. The insect removes some nutrients from the sap, with the remainder being excreted. This processed plant sap, now with a high sugar content, is called honeydew. Of course, honeydew is just a nice word for aphid manure.

Honeydew, being high in sugar, is a great growth medium for fungus. Consequently, aphid-infested plants many times turn gray or black due to fungal growth. In addition, ants prize the sugary solution as a food source. Ants collect the honeydew directly from the aphids in such an organized fashion that the aphids are sometimes called ant's cows.

Some ants go so far as to protect their aphids from parasites and predators. Other ants actually move their aphids to greener pastures. In this case, they will pick up aphids and carry them to another plant to start a new colony.

Aphids are easy to overlook because they are very small. Most are not much larger than the head of a straight pin. But what they lack in size they make up for in numbers. They are sometimes so numerous that they are often called plant lice.

Aphid populations can grow rapidly during the warm months of summer for at least three reasons. First, aphids have a short life cycle from reproductive adult to reproductive adult - as short as a few days during the summer. Also, aphids have managed to cut out the middle man in the reproductive cycle. During parts of their life cycle some female aphids do not mate. In addition, many aphids give birth to live young. All of this means there can be lots of aphids in a very short period of time.

These plant lice also have many forms, including some with wings and some without. The sharp-eyed aphid observer will also notice some female aphids with their broods, young aphids of various stages of development. Sort of the human equivalent of an extended family.

An extended aphid family group might not be a happy sight to the gardener who discovers them. But beauty is always in the eyes of the beholder.

 

Writer: Tom Turpin
Editor: Andrea McCann