To find out more about these much-maligned pests I opened my browser at
Ask Jeeves, http://www.aj.com and typed "do aphids have legs". Here is
an extract of what I found on one of the first half dozen sites listed.
This wouldn't have been written with Australia in mind, but probably is
equally applicable here. It deals with legs, wings, ants, and over-
wintering. Alas, it doesn't mention thistles, maybe because no respectable
gardener would sanction such plants in his/her plot? :-)



Aphids -- UVM Extension Entomology Leaflet 60

by G.B. MacCollom, Former Extension Entomologist, Plant and Soil Science
Department

__________________________________________________ _______________

Aphids, or plant lice, attack all sorts of annuals and perennials in the
flower garden and are present from early spring until late fall. Some are
general feeders, while others are restricted to a particular kind of plant.
Aphids are small insects, usually less than 1/8-inch in length and often
much smaller. They have sucking beaks, and their antennae are generally long
and slender. Some aphids have such long legs that they appear to be walking
on stilts as they walk about on a plant.

In spring and summer, most aphids give birth to living young, so aphids are
generally found in all stages of development feeding on the same plant at
the same time. Considering the small size of these pests, one wonders how
they can do so much harm. But when one remembers the enormous numbers
feeding on a single plant, it is easy to understand how a plant must be
weakened by them.

The stickiness noticed where plant lice are present is due to a sweetish
substance known as honey dew, which is excreted by the insect from the
posterior end of its alimentary canal. Ants are fond of this honey dew and
often follow aphids about and tap them on the back in an effort to make them
give off more of it. Honey dew imparts a shiny appearance to the foliage and
provides a base for the growth of sooty mold.

During the summer, aphids reproduce parthenogenetically; that is, males and
females do not need to mate in order that young may be produced. In the
summer, every new aphid is a female and a potential mother. For example, the
geranium aphid, in from 10 to 12 days after its birth, becomes mature and
ready to produce young of her own. Each can give birth to 30 or 35 new
aphids, and each of these is full-grown and ready to produce new aphids of
her own 10 to 20 days later. The same is true of many kinds of aphids
present in the garden. In the fall, the true sexual forms appear; males and
females mate and overwintering eggs are laid.

Aphids also produce both winged and wingless forms. In general, it is the
wingless aphids that attack garden plants. When a plant becomes
over-crowded, however, aphids are developed that have frail, gauze-like
wings. These winged forms fly to other plants, thus relieving the crowded
condition in one place but starting a fresh infestation in another part of
the garden.

One of the worst pests on roses early in the season, and a serious enemy of
potatoes later, is the pink and green potato aphid^1. This insect, one of
the larger plant lice, feeds also on aster, coreopsis, cosmos, dahlia,
gladiolus, hollyhock, iris, sweet pea, and zinnia. Its eggs overwinter on
roses. The rose aphid^2, another large and common plant louse, may be found
on roses throughout the entire year. In spring, summer, and early fall, it
feeds on the succulent leaves, stems, and buds of roses, while winter is
spent in the egg stage on rose twigs and stems. This plant louse sometimes
attacks other garden plants.

The green peach^3, or spinach aphid, is a pest of fruit trees and of
vegetable crops. It is common also in the greenhouse where it is known as
the greenfly. In the flower garden, this aphid has been found on aster,
calendula, crocus, dahlia, Dianthus, forget-me-not, iris, lily, nasturtium,
poppy, Primula, rose, snapdragon, tulip, verbena, and violet.

Other plant lice common in flower gardens, and some of the plants on which
they feed, are the melon aphid^4 (which attacks aster, hollyhock, lily,
morning-glory, and verbena) and the foxglove aphid^5 (which feeds on beard
tongue, Campanula, columbine, chrysanthemum, false dragonhead, foxglove,
gladiolus, lily, Oenothera, pansy, scarlet sage, verbena, and violet). Still
other aphids feed on lettuce, lilies, sweet peas, and garden peas. In fact,
almost everything grown in the flower garden is subject to attack by some
species of aphid.

Certain aphids feed on the roots of plants instead of on the foliage and
flowers. Root aphids generally have short legs and short antennae, and,
thus, are especially adapted for life in the soil. Where large numbers of
these insects are present, they suck out so much sap from the roots that the
plants do not receive sufficient nourishment. As a result, the foliage turns
yellow and practically no new growth is produced. Root aphids attack many
garden plants, including aster, Braille, calendula, primrose, and sweet pea,
as well as corn and strawberries. These little aphids are often attended by
ants. The ants not only look after the overwintering aphid eggs, but, in the
spring and summer, sometimes actually carry the lice through the soil from
one host plant to another. In fact, if a plant, especially an annual, looks
sickly and ants are found on the ground nearby, it might be well to hunt for
root aphids.

In the spring, it is not unusual to find plant lice on gladiolus corms that
have been stored over winter, as well as on crocus and tulip bulbs. Where
many aphids are feeding, so much sap is removed that the bulbs and corms are
considerably weakened and perfect blossoms cannot be produced.

Control

A strong force of water from the garden hose is helpful in removing aphids
from plants with stiff stems. Most of the lice that fall to the wet soil
below are unable to crawl back onto the plant. The water should strike the
under surface of the leaves, because that is where aphids are likely to
congregate. This treatment is not practical for soft-stemmed annuals such as
nasturiums.

Aphids can be readily killed by spraying or dusting with a recommended
insecticide. As different brands vary in strength, the manufacturer's
directions should be followed.

Root aphids are hard to control because they are underground pests.

etc
--
John Savage (my news address is not valid for email)