If you have ever traveled internationally, you may have noticed that before entering a country, you often need to fill out a form whether you are carrying agricultural products or have been on foreign farms during your trip. This precaution is due to the fact that many invasive plants and pests can interfere with a drive. The Asian citrus flea seed (Diaphorina citri) is an exotic pest that has spread rapidly in North America in just a few decades since it was first introduced in the late 1990s.
Psyllids are a group of insects that eat plant sap and specialize in a single host plant or a closely related family of host plants. As the name suggests, the Asian citrus flea syllable attacks citrus plants. They are also a vector or carrier of huanglongbing bacterial citrus disease (HLB). HLB is also known as Citrus Greening Disease. Infected trees show yellowing of the leaves, stunted fruit production and eventually die after a few years. There are no cures.
Together, the Asian citrus flea seed and HLB are among the most economically devastating pests for commercial citrus growers worldwide.
Asian Citrus Psyllid overview
An Asian citrus flea seed on a stem. Source: Hankplank
Asian citrus flea seed and HLB disease originate from tropical and subtropical regions of South Asia where citrus fruits originate. The Asian citrus flea syllable was first detected in Florida in the late 1990s. Now these pests can be found in much of the southern parts of the continent of the United States, the United States Virgin Islands, Hawaii, Guam, and all warm climates where citrus fruits are grown. Many plants in the Rutaceae family and the Citrus genus are susceptible, including curry leaf, grapefruit, key lime, lemon, lime, orange, grapefruit, tangerine, to name a few.
Psyllids can be misidentified as aphids, but they come from different taxonomic families. While psyllids are very small, 3-4 millimeters in length, they look more like miniature cicadas and use jumping as their primary way of moving, but can also fly short distances. Adults have bodies and wings speckled with brown. They can appear dusty as their bodies are usually covered in waxy, whitish secretions and they leave waxy feces on affected plants. The nymphs of the Asian citrus syllable are yellow or orange with red eyes. The nymphs get progressively larger with each stage or stage of development. The eggs are about 0.3 millimeters long, almond-shaped and change from light yellow to orange as they prepare to hatch.
Life cycle of the citrus syllable
Each female of the Asian citrus flea seed species can lay 300-800 eggs in her lifetime, and she lays her eggs on the growing shoots of citrus plants. Nymphs have five stages and mature in 15-47 days, depending on environmental factors. Because of their fast life cycle, these pests can have 9 to 10 generations per year – they only slow down in winter or dry months if these conditions are true.
Common living spaces
Adult Asian citrus flea seeds are typically found in large numbers on the underside of the leaves of their host plants. They are most active during the growth phase of citrus plants. Adults lay eggs on the growing tips of citrus plants and near developing leaves. The nymphs can only survive on the new growth they recently hatched on.
What do psyllids eat?
Damage from citrus green disease carried by the psyllids. Source: USDAgov
Adult Asian citrus flea seeds feed on the blushing or newly developed leaves of citrus plants. They directly affect their host plants by feeding on plant tissue. More damaging, however, they are a vector for the deadly bacterial disease huanglongbing (HLB). Because Asian citrus flea seeds feed on an infected citrus plant, they also ingest the bacteria and help spread it to other plants. While there are several types of psyllids on citrus plants, the Asian citrus flea seed is the only type that can transmit HLB. All it takes is a few flea seeds to cut an entire tree.
Nymphs feed on the sap of plant tissue from the growing tips of plants, immature leaves, soft stems, and flowers. During feeding, they also inject a saliva toxin into the plants, which deforms or dies the new flushing tips of their host plants. Damage to the new flush of citrus leaves slows the plant's growth. A tell-tale sign of these nymphs is the waxy, curly tube with a lightbulb from the back of their body that they produce to get rid of waste.
How to control Asian citrus flea seeds
Because of the significant threat that Asian citrus flea seeds pose to the US citrus industry, there are many national and state efforts to quarantine and monitor these pests. The website of your local Agriculture Commissioner has dedicated hotlines to call if you suspect your trees are infected. For example, throughout the state of California, HLB has been registered in residential areas, and there are several PSAs that have been created by the state to help home gardeners identify and report the problem. There is no cure for HLB, so the only way to treat the disease is to reduce the population and spread of psyllids.
Check the growing tops of your citrus trees carefully and often. Check the new leaves are flush and the underside of delicate new leaves and twigs. Psyllids and nymphs are very small, so you may need to examine your plants with a magnifying glass. Pay special attention to the waxy tubules produced by Asian citrus flea nymphs.
Organic or chemical control
Diaphorina citri is a vector for HLB, Citrus Greening Disease. Source: Hankplank
Home gardeners can use horticultural oils, insecticidal soaps, and pyrethrins, but the spray must be in direct contact with psyllids to be effective. Due to the fast life cycle of Asian citrus flea seeds, these control methods need to be sprayed every 7 to 10 days while new leaves flush and grow. These methods are usually not as effective as other chemical controls.
Foliar sprays such as Sevin and Malathion or imidacloprid-soaked soil can be used to control Asian citrus flea seeds. However, these are not organic insecticides. The most effective treatment for Asian citrus fleas is a combination of soil watering and foliar sprays used by professionals.
Environmental control
The Asian citrus flea seeds have natural predators, including lacewing larvae, syrphid larvae, spiders, birds and ladybugs. Creating an environment in your home garden that supports these beneficial natural enemies is a great way to reduce psyllid populations.
On a larger scale, one of the most promising biological controls is Tamarixia radiata, a small parasitic wasp. The female wasps lay their eggs under or in Asian citrus flea seed nymphs, and the growing wasp larvae feed on the nymphs from the inside out, leaving behind a hollow "mummy bowl". In California, researchers from the University of California Riverside worked with the California Department of Food and Agriculture to raise these wasps and release them into residential areas in Southern California.
Be aware that ants feed on honeydew and tubules produced by Asian citrus flea nymphs and defend them to protect this food source. If you know that parasitic wasps have been released in your area by your local agricultural service, you will need to control the ant population in your garden to keep these wasps effective.
Prevent psyllids
If you think your citrus tree is showing symptoms of HBL, you need to call your local helpline ASAP to have a leaf sample tested. Maps are also available from the Agriculture Commissioner's office that document where infections have already occurred in your region. If there is a documented case of HBL within 2 miles of your trees, it is likely that your plants have already been infected. Trees may not show symptoms of HLB immediately. Therefore, if your trees are already infected, you should have your trees tested and removed to prevent HLB from spreading to neighboring trees.
frequently asked Questions
A close-up of a citrus syllable on a curled leaf. Source: Hankplank
Q: How do I protect my citrus trees from insects?
A: One of the best ways to protect your citrus trees is through frequent inspections, especially during the growing season. Use a magnifying glass to thoroughly check the growth tips for adults, eggs, and nymphs. Apply the treatment directly to the pests.
Q: What do Asian citrus fleas eat?
A: Asian citrus flea seeds eat plant tissue from the new growing areas of citrus trees. Your nymphs also eat sap from flowers and stems.
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