Oleander aphid (Aphis nerii)

Oleander aphid (Aphis nerii), sometimes called euphorbia aphid, is a common pest of several significant ornamental plants of the families of cuttle (Apocynaceae) and gusset (Asclepiadaceae). This bright yellow aphid with black appendages is usually found on oleander, Nerium oleander, milkweed, Asclepias tuberosa and tropical milkweed, Asclepias curassavica.

Distribution

Oleander aphids are cosmopolitan, they can be found in tropical and moderately warm regions around the world. This species probably originated in the Mediterranean region, from where its main host plant, oleander, originates. In Poland, oleander aphids were registered only in greenhouses. Small populations of oleander aphids have been recorded in London gardens.

Description

It is believed that the oleander aphid is an obligate parthenogenetic species; thus, all adult aphids are females, and males are not found in the wild. Adult females can be winged and wingless. Winged adult females are yellow-black with dark veins on the wings, while wingless forms are yellow with black cores, antennae, legs, and tail (tip of the abdomen). Nymphs are similar in appearance to adult wingless females, except that they are smaller. The size ranges from 1.5 to 2.6 mm in length.

Life cycle

Females are viviparous and reproduce parthenogenetically, which means that they lay nymphs, not eggs, and that the offspring are clones of an adult female (Sexual reproduction is not necessary for the production of offspring). Nymphs feed massively on the plant and rapidly increase the population of the colony. The pest has 5 stages of development of the nymph, through which it passes in the process of growing up. Like all aphids, they do not have a pupal stage, and adults appear during the final moult of the nymph. Usually wingless individuals appear. Winged individuals appear in case of overpopulation and unsuitability of the plant, which allows aphids to migrate to new host plants. The parthenogenetic method of reproduction, high fertility and short generation time allow large colonies of oleander aphids to grow rapidly on infected plants.

The damage caused

The range of oleander aphid hosts includes several genera of Asclepiadaceae and Apocynaceae, including plants such as oleander, milkweed, and periwinkle. The pest can often be found on plants of the Asteráceae, Convolvuláceae and Euphorbiaceae families. In addition, it has been found on citrus fruits. This aphid can carry various viruses, including the sugar cane mosaic potyvirus.

Oleander aphids feed on the juice of the phloem of the host plant. The damage caused by aphid colonies is mainly aesthetic in nature due to the large amount of sticky honeydew produced by colony members and the resulting black sooty mould that grows on these secretions. In addition, plants can deform. Most of all, agrarian spheres are concerned about the possibility of stunting plant growth due to repeated severe infection throughout the year.

Control

Cultural control measures are a good means of combating oleander aphid infestation. Reducing the amount of watering, pruning, and fertilizers will reduce the formation of tender shoots, which are the favourite food of oleander aphids. On smaller plants grown as sources of nectar, the infected shoot can be cut and discarded, or aphids can be displaced by a strong jet of water.

Natural biological control is very effective in combating populations of oleander aphids. There are a number of entomophages that are natural enemies of aphids, among which there are also parasitoid wasps that lay eggs in aphid nymphs. The parasitized aphid turns into a light brown swollen mummy, and the parasitoid develops inside this mummy. A new parasitoid wasp appears when the aphid’s body is eaten. In addition, universal insects are predators, such as larvae of syrphid flies (Syrphidae), green and brown lacewings (Chrysopidae), larvae and adult individuals of ladybirds (Coccinellidae).

Oleander aphids isolate cardiac glycosides, recognized cardiac poisons, from host plants. They also enhance the secretion of their corneas with these bitter, poisonous chemicals. Their bright aposematic (warning) colouration and the presence of toxins protects them from predators from some species of birds and spiders. Spiders that have this secret applied to the oral apparatus immediately retreat and try to clean it. These cardiac glycosides do not seem to harm parasitoids and universal insect predators associated with oleander aphids.

Insecticidal soaps and oils are often effective against soft-bodied insects such as aphids. Insecticides are usually not necessary in a home garden, given the high level of natural biological control, the ease of destroying aphids with insecticidal soap and oils.