Nature Bulletin No. 421-A May 29, 1971
Forest Preserve District of Cook County
George W. Dunne, President
Roland F Eisenbeis, Supt. of Conservation
Aphids, or Plant Lice, are tiny defenseless insects that have soft bodies
but needle-like beaks with which they puncture plants and suck the
sap. They weaken or even kill many plants and also may infect them
with virus, bacterial or fungus diseases. Aphids, unless controlled,
multiply enormously and cause serious damage in orchards, vineyards,
truck farms, gardens greenhouses, and field crops such as corn, cotton,
small grains, clover and alfalfa.
There are hundreds of species of aphids distributed over the world and
there is scarcely a kind of plant, wild or cultivated, that is not infested
by one or more kinds of plant lice. Some feed on stems and leaves,
some on the roots, and some on both. Others feed on buds, and a few --
like the Hickory Aphid which infests hickory, maple and other forest
trees -- feed on bark underneath the limbs. The hickory aphid is about
one-quarter of an inch long, and one of the largest, but most kinds are
about the size of a pinhead: less than one-twentieth of an inch in
length. Most species are green but many are pink, white, brown or
blackish. The woolly aphids, which feed on apple, pear, hawthorn and
elm trees, are reddish or purplish but cover themselves with a cottony
white secretion of wax.
Aphids have a strange life cycle. It differs considerably according to
the species but, in our northern climate, most kinds pass through
winter as eggs laid on a particular kind of plant. When warm weather
comes, these hatch out small nymphs which soon grow to full size but
never have wings. All of them are females, called "stem mothers"
because they have the remarkable ability to produce, without mating,
young which are born alive and which are wingless like themselves. In
a few days these, too, are producing wingless females at the rate of
several per day. That goes on and on. There may be 20 or more such
generations in a single year, with each female producing as many as
50 or eve 100 young.
However, during summer, some females develop wings and fly to other
plants where, without mating, they produce young and start new
colonies. Some species select plants like the one on which they were
born which includes both males and females, all with wings. In some
species these have no mouth parts and cannot eat. After mating, before
they die, the last females each lay from one to four eggs which hatch
next spring and start new colonies.
In addition to controlling them with sprays and dustings of nicotine
compounds, DDT and some newer insecticides, aphids are often kept
in check by natural enemies such as lady beetles, the larvae of "sweat
flies" and lacewings, and parasitic wasps even smaller than the aphids
Among the many other interesting things about aphids is how they are
used, with almost human intelligence, by ants Aphids secrete a sweet
sticky fluid called "honeydew". The Corn Root Aphids, and the
Strawberry Root Aphids, for instance, are nurtured by the small brown
Cornfield Ant which "milks" them of their honeydew, moves them to
new pastures when necessary, and stores their eggs during winter.
When the young aphids hatch in spring, they are moved to the roots of
grasses or smartweeds to feed until young corn or strawberries are
available. The only way to control the aphids is to destroy the ants and
Aphids is dumb but ants is smart!
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Update: June 2012