Black Citrus Aphids

All aphids are bad, but invasive black citrus aphids can kill your orange tree.

Well, not exactly.

Black citrus aphid adults and nymphs (Scot Nelson) Public Domain

Black citrus aphids (Toxoptera citricida) are vectors for citrus sadness, a potentially fatal disease of grapefruit, lime, lemon, and orange trees. They spread this disease as they feed on the sap found in new leaves and tender buds. And that feeding causes damage of its own, weakening trees, stunting growth, and generating honeydew. That honeydew provides the perfect growth medium for sooty mold and other fungal diseases, which block photosynthesis. Black citrus aphids are considered one of the world’s most serious citrus pests.

Originally from southeast Asia, this pest is now found in Africa, Australia, India, and Central and South America. In 1995, black citrus aphids appeared in Florida, where they are now well established. It is estimated that these pests will devastate the California citrus industry if they find their way across the Rockies. This is one reason why you have to wait in line at the agricultural inspection stations when driving across some state lines.

Black citrus aphid (Florida Department of Agriculture, Bugwood.org) CC BY 3.0

Black citrus aphid identification

Also known as oriental citrus aphids and brown citrus aphids, they get the different color names because they change color as they develop. Adult black citrus aphids are black and shiny. Like other aphids, they can be winged or wingless. Nymphs are reddish-brown. And there are no eggs unless they live in Japan.

Black citrus aphid lifecycle

All black citrus aphids are female, and all of those females give birth to live young unless they live in Japan. For some bizarre reason, black citrus aphids occurring in Japan do lay eggs. In either case, those populations can explode in record time. It is estimated that a single black citrus aphid can produce more than 4,400 offspring in three weeks. Those offspring can start reproducing on their own when only one week old. You can see how things could quickly get out of hand. The network effect of all that reproduction can result in 600 billion aphids in a single season, all starting with one aphid.

Managing black citrus aphids

One way to reduce aphid problems is to only feed nitrogen to plants at the appropriate times and avoid shearing citrus trees. Shearing and nitrogen both stimulate vulnerable new tip growth. Also, ants protect aphids. You can eliminate that protection by wrapping the trunks of citrus trees with sticky barriers. You can also use sticky sheets hung in your citrus trees to monitor for winged aphids and other pests.

Natural predators, such as ladybugs, and parasitic wasps will help reduce aphid populations. You can attract these beneficial insects to your garden by installing insectary plants, providing water, and avoiding the use of broad-spectrum pesticides.

A powerful stream of water from your hose can dispatch large clusters of aphids which are then unable to return to the tree, but this treatment won’t get them all, and it only takes one. Insecticidal soap can also be used, but that treatment is only effective on the aphids it touches.

Monitor your trees regularly for signs of black citrus aphids and report any potential sightings to your local County Extension Office right away.