**Oleander Aphids** (*Aphis nerii*) are bright yellow, soft-bodied, sap-sucking insects that are specialized pests of plants in the dogbane family, most notably **Oleander** (*Nerium oleander*) and milkweed. The conflict is primarily aesthetic: they infest new growth, sucking plant sap, which causes **stunting, distortion of leaves**, and massive amounts of **honeydew** excretion. The honeydew then promotes the growth of unsightly black sooty mold, reducing the ornamental value of the plant and creating sticky residue on surfaces below.
Taxonomy and Classification
Oleander Aphids belong to the order Hemiptera (True Bugs). They undergo simple metamorphosis. They reproduce year-round through parthenogenesis, forming extremely dense, visible clusters on tender growth. Their bright yellow color is hypothesized to be a warning coloration to predators, reflecting the toxins sequestered from their host plants.
Physical Description
Adult aphids are tiny, 1.5-2.5 mm long.
- **Appearance (Key ID):** Distinctive, shiny **bright yellow** or orange body with black legs and black cornicles (tailpipes). They are found in dense colonies.
- **Habitat (Key ID):** The new terminal growth, flower buds, and undersides of the newest leaves.
- **Damage Sign (Key ID):**
- **Black Mold:** Black, soot-like fungal growth on leaves and stems (feeding on honeydew).
- **Sticky Mess:** Visible sticky, clear honeydew dripping onto sidewalks and cars.
- **Distortion:** Curled, stunted, or yellowed new growth.
- **Conflict:** Aesthetic damage, sooty mold, and high nuisance.
Distribution and Habitat
Oleander Aphids are found worldwide in subtropical and temperate climates. Their habitat is restricted to Oleander, milkweed, and a few related ornamental species in landscapes and gardens.
Behavior and Conflict
The conflict is high population density and aesthetic mess.
- **Toxin Sequestration:** They feed on the toxic sap of the Oleander plant, which makes them unpalatable or toxic to many generalist predators, though specialized predators (like lady beetles) still consume them.
- **Year-Round Breeding:** In warm climates, they breed continuously, leading to rapid, constant infestation.
- **Ant Association:** They are readily tended by ants in exchange for honeydew, which interferes with natural biological control.
Management and Prevention
Control is integrated pest management (IPM), favoring manual and biological controls.
- **Water Spray:** Use a strong jet of water to knock the clusters of aphids off the new growth. Repeat every few days until populations subside.
- **Pruning:** Prune off heavily infested tips and destroy them.
- **Natural Enemies:** Protect and encourage natural predators (lady beetles, parasitic wasps, lacewing larvae), which are highly effective at regulating their population.
- **Horticultural Soap/Oil:** Apply insecticidal soap or a light horticultural oil to the infested areas (ensure complete coverage to break up the clusters and kill by contact). Repeat as needed due to continuous reproduction.
Conservation and Research
Oleander Aphids are managed as ornamental pests. Research focuses on their relationship with their toxic host plant, understanding their dispersal mechanisms, and optimizing the use of natural predators in landscape management.