Whiteflies are major agricultural pests that can wreak havoc on your garden and landscaping. These tiny, mothlike insects eat plants and multiply quickly. Without timely intervention, whiteflies can transmit plant diseases and even kill crops. You can protect your garden or farm by learning how to recognize, prevent, and control whiteflies.
What Are Whiteflies?
Despite their name, scientists don’t consider whiteflies true flies. Instead, the insects belong to the suborder Homoptera. This suborder contains over 6,000 species of North American insects, including aphids, cicadas, and leafhoppers. All Homopteran insects have piercing/sucking mouth organs that they use to drink sap from plants.
There are over 1,500 whitefly species, but most don’t spread plant viruses. In North America, common whitefly varieties known to transmit disease include:
Greenhouse whiteflies (Trialeurodes vaporariorum). This species is the most widespread whitefly in northern regions. Greenhouse whiteflies eat a variety of popular flowers and vegetables, including coleus, cucumber, fuchsia, hibiscus, lettuce, poinsettia, and tomato. This diet makes these pests a nuisance for many farmers and hobby gardeners.
Silverleaf whiteflies (Bemisia argentifolia). This species eats more sap than other whiteflies and causes severe plant damage. Plant growers commonly call these insects silverleafs because squashes turn silver after the whiteflies feed on them. Silverleaf whiteflies also cause phytotoxemia in poinsettia plants. Scientists refer to this variety as the B-biotype whitefly.
Sweet potato whiteflies (Bemisia tabaci). Also known as the Q-biotype, these whiteflies likely originate in the Mediterranean region. Scientists first detected this species in the U.S. in Arizona in 2004. Sweet potato whiteflies are immune to pyriproxyfen, an insect growth regulator, and have developed resistance to several common insecticides. As a result, this species is difficult to control.
Bandedwinged whiteflies (Trialeurodes abutilonea). These whiteflies closely resemble greenhouse whiteflies but have different wing markings. Bandedwinged whiteflies eat most plants, including cotton, geranium, hibiscus, petunia, and velvetleaf. While this species was once prevalent in North America, the introduction of synthetic insecticides in the 1940s significantly reduced its population. But gardeners still occasionally encounter bandedwinged whiteflies in greenhouses and landscaping.
Where Do Whiteflies Live?
Whiteflies are adaptable tropical insects that thrive in warm climates around the world. Affected regions include:
- Africa
- Asia
- Australia
- Europe
- Mediterranean
- Middle East
- North America
- South America
The widespread distribution of whiteflies makes these pests a severe threat to global agriculture systems and economies. For example, several species of these pests live in sub-Saharan Africa. They transmit cassava mosaic disease and cassava brown streak disease in Kenya and other areas. These two diseases cause over $1 billion in damage yearly.
What Do Whiteflies Look Like?
The appearance of whiteflies varies depending on their life stage. The insects lay white or light tan eggs on the underside of plant leaves. These eggs darken to blue or purple before hatching.
The newborn whiteflies look like tiny scale insects with flat, oval, greenish-yellow bodies. As they grow, immature whiteflies darken to cream or yellow.
All whitefly species look like miniature moths when they reach maturity. They have four white wings, two segmented antennae, and a yellow body. A white, waxy powder coats their bodies.
What Do Whiteflies Eat?
Whiteflies feed on over 1,000 known species of host plants. They target fruits, ornamental plants, vegetables, and other vegetation.
Here’s a small sample of common whitefly host plants:
- Ash
- Broccoli
- Cabbage
- Dogwood
- Pumpkins
- Redbud
- Roses
- Squash
- Sycamore
- Tomatoes
Whiteflies inject enzymes into the plants and suck juices from leaves, weakening the plants over time. They also excrete a sticky substance called honeydew, which can cause the plant to grow mold.
What Are Whiteflies’ Life Cycle?
Whiteflies have a lengthier life cycle than many pests. In warm temperatures, their life cycle is 2 and ½ weeks to 3 weeks. During cooler temperatures, their life cycle can last up to 2 months.
The whitefly life cycle includes several distinct stages:
Eggs. Female whiteflies lay 6 to 20 eggs daily on the leaves of host plants. Eggs generally hatch in 7 to 10 days.
Crawlers. Nymphs emerge from the hatched eggs. They settle into a nearby plant and embed their beaks into the tissues for feeding. They remain in the same spot for a month as they develop through four more stages, becoming pupae.
Pupae. In the last life cycle stage, the pupae undergo simple metamorphosis and transform into adult whiteflies.
Because whiteflies reproduce so quickly, plant growers may encounter several overlapping generations.
How Do You Identify Whiteflies?
You can identify whiteflies by spotting the insects in your garden or noticing symptoms in your plants. The various species of whiteflies have subtle physical differences. For example, adult bandedwinged whiteflies have brown stripes on their wings, but greenhouse and sweet potato whiteflies don’t have markings. And greenhouse whiteflies hold their wings together without spaces between them, while silverleaf and sweet potato whiteflies have gaps between their wings.
Checking your plants for symptoms is another effective method of whitefly identification. Classic signs of whitefly damage include:
- Chlorotic spots
- Leaf yellowing
- Shedding leaves
- Stem blanching
- Dying plants, in severe cases
You may also notice that your plants have developed diseases frequently transmitted by whiteflies, such as:
- Begomoviruses
- Cowpea mild mottle
- Criniviruses
- Ipomoviruses
- Pepper whitefly-borne vein yellows virus
- Torradoviruses
Examine your plants regularly so you can quickly spot and get rid of a whitefly infestation.
How Do You Get Rid of Whiteflies?
If you suspect that you have whiteflies, don’t panic. There are several strategies that you can use for whitefly control, including:
Insecticides. Many plant growers use chemical compounds to eliminate whiteflies. Popular compounds include Celero (clothianidin), Marathon (imadacloprid), and TriStar (acetamiprid). Switching chemicals with every application is the way to prevent the whiteflies from developing resistance.
Biological control methods. You can release parasitoids, pathogens, or predators like lacewing larvae into your garden or greenhouse to kill whiteflies. You can purchase these biological agents from gardening suppliers.
Prevention. Basic sanitary and safety measures can shield your crops from whiteflies. Always check new plants carefully for whiteflies before you bring them into your garden or greenhouse. Keep your growing area tidy and remove any leftover plant material after the growing season to prevent whiteflies from reproducing. Finally, you can install screens with holes smaller than 0.19 millimeters in greenhouse vents to keep pests out.
By staying vigilant and using control methods, you can help protect your plants from getting damaged or wiped out by whiteflies.