Aphids/ Plant Lice

Yellow aphids

Aphids on growth tip

Aphids on apical tip of plant

Aphids on Calotropis

Adult black aphid

Aphid exoskeletons

Aphid being paratised by wasp

Adult winged aphid

Common name: Aphid/ Plant Lice

Classification: Superfamily: Aphidoidea

Physical description

Aphids are small soft-bodied, sap-sucking insects that normally occur around the actively growing tips of plants or under leaves near the apical point/ buds. There are numerous types of Aphids, each with their own characteristic color and body markings, they are also often referred to as “Plant lice”. Generally, they are 1 to 3mm in size. They are gregarious, large populations build up very quickly in sheltered, warm conditions.

Description of damage

Aphids feed by inserting their sucking mouthparts (stylet) into the stem or leaf of the plant; they then feed off of the plant sap, much like a hypodermic syringe sucking the sap. The cell sap is high in Nitrogen and is used by the insect to grow and reproduce; this is why they are often found near soft, actively growing tips as plant nutrients are in much higher concentrations in these portions of the plant. Aphid damage can be seen as stunted or deformed leaves normally occurring at the apex of the plant; in most cases, the symptoms persist after the insects have moved off or been killed.

Life cycle description

Young insects are borne alive through an asexual process called parthenogenesis. This means that a female insect can give live birth to an almost indefinite number of sexually mature offspring (normally males). Aphids do not undergo metamorphosis like some other insects and the newly born young look like their adult counterparts; they are normally paler in color, but as they age, they molt and shed off their exoskeletons - these can sometimes be seen as small white dried husks in and around a colony of insects. Only when food is in short supply or the population has grown too overcrowded are more females produced. The females are winged; they mate and can fly off to a new host plant. When they do lay eggs, these are able to over winter, or in our case over summer, and hatch at a later time, eggs are normally impervious to any kind of insecticidal treatment.

Plants affected

Fast-growing, soft-tissue plants are preferred (so young plants and seedlings are often food sources); however, some Aphid species are able to feed on harder plant tissues (such as Oleander and Calotropis), they will even attack certain types of ornamental grasses.

General comments

The excrement of the Aphid is sometimes called “honeydew”, this is excreted from the rear of the body; ants are sometimes found in attendance and remove the honeydew due to its high sugar content. This is a symbiotic relationship, the ants tend and protect the Aphids, and in return, they receive the honeydew. If the honeydew is uncollected it can form pools around the insect, or fall onto the leaves below where they are feeding, this then acts as a substrate for fungus or mold to grow on. This secondary condition of a fungus/ mold growing on the leaves below the Aphids can also harm the plant as this blocks out light to the leaves and inhibits photosynthesis.

Control methods - Natural

Aphids are predated on by an array of “beneficial” insects, such as Ladybugs (both the adult and larval stage), wasps, and spiders.

Control methods - Cultural

Aphids are easy to kill, simply brushing or hosing them from a leaf once they have inserted their mouthparts will break the stylet off in the leaf, and the Aphid will be unable to feed and will die.

Control methods - Other

Aphids can also be controlled through the application of products such as Neem oil, or even by applying a light soap water solution (1ml liquid soap in 1 liter of water), as the mixture is hydrophilic it sticks to the bodies of the small insects, and blocks their spiracles which they use for breathing, effectively suffocating them.