Issue 10, September 11, 2020
Whiteflies
In the coming weeks, you may notice a cloud of tiny white specks emerge from plants in your yard. These tiny insects are whiteflies. While they have the word “fly” in their name, they are more closely related to aphids, scales and mealybugs. Like aphids and scales, they suck fluids from plants with straw-like mouthparts and produce sugary, liquid droppings called honeydew. In large populations, they can become pests of vegetables, ornamentals and greenhouses.
Greenhouse whitefly (Trialeurodes vaporarorium), Whitney Cranshaw, Colorado State University, Bugwood.org
Adult whiteflies are tiny winged insects, about 1/16 of an inch long. They are white with powdery white wings held over their body like the roof of a house. Females leave their mouthpart inserted into the plant and move their abdomen while laying eggs. As a result, eggs are deposited in a circular pattern of 30 - 40 eggs.
Nymphs, called crawlers, hatch from the eggs and walk on the surface of plants before inserting their mouthparts on the underside of a leaf, where they molt to become stationary nymphs. During the last instar, the nymph ceases feeding and undergoes physiological changes, making this life stage functionally similar to the pupal stage in insects that go through complete metamorphosis. During this stage, they are flat discs, often with pale, waxy fringe. When adults emerge, they can live for about a month.
Bandedwinged whitefly (Trialeurodes abutiloneus), Nancy Gregory, University of Delaware, Bugwood.org.
Three common species of whiteflies in Illinois are the greenhouse whitefly (Trialeurodes vaporarorium), silverleaf whitefly (Bemisia tabci; also called sweet potato whitefly) and bandedwinged whitefly (Trialeurodes abutiloneus). Bandedwinged whitefly is the most common species in Illinois. It can be identified by the two dark bands on each of its forewings. They feed primarily on velvetleaf but move to alternate hosts later in the season. They do not reproduce heavily on alternate host plants and usually do not require control. In some cases, control may be warranted on velvetleaf and flowering maple in the genus Abutilon.
Greenhouse whitefly and silverleaf whitefly lack the dark banding and are completely white. They are unable to overwinter in Illinois but can survive in greenhouses and are moved outdoors with plants in the spring. Because they have multiple generations throughout the growing season, their populations can become quite large by late summer and fall and have the potential to damage ornamental plants.
Damage appears as wrinkled, curled or cupped leaves. Large populations can also produce large quantities of honeydew making the surface of plants sticky and prone to sooty mold growth.
If whitefly populations are high late in the growing season, they are unlikely to cause significant damage and do not require treatment. However, if both significant aesthetic damage and nymphs are present on the plants, greenhouse whitefly or silverleaf whitefly may warrant control. Treatment should target nymphs. Insecticidal soap and summer oils are effective treatments for whiteflies. Apply them according to the product label, which may require a weekly application for two to four weeks. Chemical insecticides like pyrethroids are also effective when treatment is warranted.
Author:
Sarah Hughson