Description

There are a few thousand species of aphids of which around 200 to 300 species are crop pests. All aphids are small, soft-bodied, and tear-drop or pear-shaped. The colour of aphids depends on the species or can sometimes be determined by what they are feeding on. They may be black, yellow, brown, green or even red. A distinctive feature is the tube-like extensions from the rear of their abdomens called cornicles. These secrete pheromones or liquids which are not liked by predators as a defence mechanism. Aphids are generally wingless but if they start to overcrowd a host plant, winged aphids will be born. These aphids are then able to fly onto new plants and start a new colony. Mirid bug nymphs, of which there are good and bad, look very much like aphids but they do not have the cornicles. One species, the woolly aphid has a waxy, fluffy coating which looks like wool, hence its name. Aphids excrete honeydew which is a sticky, sugary liquid. Species include: bean aphid (Aphis fabae), cabbage aphid (Brevicoryne brassicae), citrus aphid (Toxoptera citricida), pea aphid (Acyrthosiphon pisum), potato aphid (Nacrosiphum euphorbiae), melon aphid (Aphis gossypii), green peach aphid (Myzus persicae)

Adult size: 1-3mm

Out and about

In spring and autumn when the weather is mild and warm but possibly in more temperate areas they may be about for longer periods as they don’t like hot temperatures. They can be found in temperate and tropical regions worldwide. Aphids are widespread throughout all states of Australia.

Reproduction and Life cycle

Females are able give birth to live young, which in turn will also produce live young. At times males will mate with females in autumn and the eggs will hatch the following spring. Some males also hatch so that the cycle can start again the next season. There can be several generations where only female aphids hatch from eggs. They infest plants very quickly because of this ability to reproduce at a phenomenal rate.

To deter

To control

Since aphids breathe through their bodies, oil based products will coat them and suffocate them. Spray with: - soapy water - white oil - neem oil - tea of garlic, nettles, basil, or wormwood - pyrethrum can be used if the infestation is bad, but it will also harm the beneficial insects, especially bees. It is a good practice to spray in the late evening when these are less likely to be around. Keep weeds under control- milk thistles attract aphids as a host plant. Encourage predators, particularly ladybirds, by planting appropriate plants Sooty mould can be treated with a soap spray, white oil or neem spray, all of which prevent the fungal spores from germinating. Milk thistles attract aphids as a food source where they will breed up and then often transfer over to the garden.

Plants to repel

Aromatic herbs planted near crops Basil / Catnip / Chives / Coriander / Dill / Mint / Nasturtium / Parsley Plant members of the onion family among susceptible crops

Plants to attract

Predators

Aphidius wasp / Aphidoletes / Damselbugs / Damsel fly / Dicyphus, hoverflies / Lacewings / Ladybirds / Minute pirate bug / Big-eyed bug

Why they are a Pest

Aphids suck the sap from plants by puncturing the surface with their piercing mouth parts, excreting the excess as honeydew. Many species are crop-specific but others are not so fussy feeding on a great variety of plants. The plants can become infested very quickly. They can do considerable damage before predators move in. They cause leaf distortion and deformities in new growth which can affect buds, flowers and fruit. Aphids can transmit plant viruses, as a result of their piercing and sucking mouthparts, if they are dispersed from one plant to another. Sometimes aphids can be carried on the wind or, on heavily infested plants, when populations become too big or the food supply is depleted, some species will produce offspring with wings to aid active dispersal. Ants use the sweet honeydew from the aphids as a food source, ‘farming’ the aphids and protecting them from predators. Some ants will take aphid eggs back to their nests for the winter and in spring when new aphids have hatched they will carry them to plants and continue farming the new generation. The presence of ants on plants will, by association, indicate aphids, scale and/or mealybugs. The honeydew itself can grow a fungus called sooty mould, which will not kill the plant but it will inhibit photosynthesis.