Aphids are representative of a group of insects that acquire their food by piercing plant or animal tissues with sharp mouthparts and sucking up the body fluids. To gardeners and farmers, aphids will be serious pests. The gardener will be acquainted with 'greenfly' on roses and 'blackfly' on broad bean plants.
Life cycle. Within the summer months, all the aphids seen will be females and most of those on plants can be wingless. They reproduce at now by a process called 'parthenogenesis' in which no sexual method occurs. The females don't lay eggs but deliver their young, known as nymphs, alive.
The nymphs are like miniature adults and soon reach full size when a series of 'moults'. Once in a while, some of these nymphs develop wings and fly off to infest new plants.
In Autumn, some of the winged forms are males that fly off to a close-by tree or shrub. They are joined by winged females that produce wingless daughters. These daughters then mate with the males and lay eggs on the branches of the tree. The eggs have thick shells and can face up to low temperatures throughout the winter. In Spring, the eggs hatch to wingless females that kill the young tree leaves, producing daughters parthenogenetically. A number of these daughters can be winged and fly away to reach the plants on that they feed during the Summer.
Feeding. Aphids have elongated mouth elements that fit along to create a piercing and sucking tube, a proboscis. On a leaf, they insert this proboscis through the leaf tissue till it reaches the food-conducting cells (phloem cells). They inject a very little saliva that starts to digest the cell contents and then suck up the fluid into their gut.
The plant sap contains more sugars than amino acids (protein precursors) and therefore the aphids excrete a resolution of the surplus sugar through their anus. This liquid is popularly known as 'honey dew' and when it falls on the leaf, it encourages the expansion of mould. But, ants have a great liking for this 'honey dew' and clamber over the feeding aphids to gather it.
The feeding habits of aphids damage the leaves, creating them curl up, dry out and fall off. This result as well as the fact that the plant is deprived of a number of its nutrients will cause a loss in yield from crop plants and vegetables. Aphids additionally unfold plant viruses by their feeding habits.
Control The aphids are preyed upon by ladybirds and their larvae and also the larvae of lacewings. These predators control the aphid population to some extent but gardeners and farmers usually have to resort to pesticides. Some of these simply kill the aphids on contact and might be as innocuous as soap solution. Since the aphid penetrates the plant leaf in order to feed, spreading insecticide on the leaf surface is ineffective and recourse is made to systemic insecticides. The plant absorbs these insecticides into its tissues so that the aphid is poisoned when it takes up the cellular fluids. The insecticides break down after a short time so they are not gift within the harvested crop.
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Dorish Hill Grant has been writing articles online for nearly 2 years now. Not only does this author specialize in Biology, you can also check out his latest website about:
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