Whiteflies are not true flies (Diptera) but rather are piercing-sucking insect pests (Hemiptera, Family Aleyrodidae). They are more closely related to the aphids, scale insects, and mealybugs. Adult whitefly wings and bodies are covered in a white, waxy substance. Whiteflies can develop quickly under warm conditions. The life cycle and host plants of these insects depends upon the species. The rhododendron whitefly (Dialeurodes chittendeni) and its biology is featured here. Management options specific to the rhododenron whitefly are discussed elsewhere in this Guide.
The rhododendron whitefly can be a significant pest of its namesake host in the US. It was first reported in the United States in 1932 on rhododendrons from England; however, the insect may be native to parts of Asia. Reports from British Columbia indicate that rhododendrons brought from Kent, England in 1933 and 1934 were slightly infested with this insect. Adult females lay their elongate-oval, smooth eggs on the undersides of host plant leaves, attached with a short stalk. Nymphs hatch from these eggs and adhere themselves to the leaf underside, where they feed the entire time until adulthood. The immatures may look like and be confused for scale crawlers on the leaf undersides; they are semi-transparent, elliptical in shape, and become rounder as they mature. A single generation of the rhododendron whitefly may occur per year. The overwintering life stage is the immature nymph. Nymphal instars may overlap in their timing at a single location during the growing season, leading to variation. The final nymphal stage (immature) is sometimes referred to as a "pupae"; however these insects do not undergo complete metamorphosis. This final nymphal stage ("pupa") is transparent, white, and papery and 1.25 mm long. Stout spines are found along the edges of the "pupa" and tiny legs and mouthparts may be examined with magnification. Adults are present from mid-May to early August and are dusty-colored (white wings that are 8 mm across and a yellow body). Adults are said to be extremely active during sunny weather (Olds, 1935). When disturbed, the adults may fly around the infested shrub and then quickly settle back on the undersides of the leaves. Adults may be capable of short-range independent movement, however longer distance dispersal is likely human-aided.
Whiteflies use their piercing-sucking mouthparts to remove host plant fluids. Large populations of whiteflies can cause host plant leaves to yellow in color, dry out, and eventually drop from the plant. Whiteflies excrete a sugary liquid waste known as honeydew, which can coat host plant surfaces. Black sooty mold (a fungus) can develop on the honeydew, on which it feeds. On most ornamental trees and shrubs, natural enemies of whiteflies keep their populations in check so that severe damage to the overall health of the host plant does not occur. As such, chemical management options are rarely needed for these insects in ornamental landscapes. In fact, chemical management options that disrupt the balance of whitefly natural enemies may lead to whitefly outbreaks (Flint, 2021, UC IPM Fact Sheet).
Yellow sticky traps can be placed in ornamental landscapes to help monitor for adult whiteflies. Place them close to the host plants of concern. These are for monitoring purposes only, and typically do not significantly reduce the number of whitefly adults through trapping.
Remove host plants that have repeated and elevated infestations of whiteflies. These may act as a reservoir for these insects which are typically kept beneath damaging levels by natural enemies. Individually infested leaves can be picked off plants and destroyed to help remove non-mobile life stages of these insects. Syringing (or spraying the insects with a strong jet of water from a hose) is also sometimes suggested for whitefly management.
General predators of whiteflies include but are not limited to: lacewings, bigeyed bugs, minute pirate bugs, and lady beetles. Tiny parasitoid wasps (such as those in the genus Encarsia) may parasitize certain species of whitefly as well (Flint, 2021, UC IPM Fact Sheet). The specific natural enemies depend upon the species of whitefly of concern. If considering chemical management options for whiteflies, choose reduced risk insecticides in order to conserve important natural enemy populations.
Abamectin (NL)
Acephate (NL)
Acetamiprid (NL)
Azadirachtin (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Buprofezin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Chromobacterium subtsugae (NL)
Clothianidin (NL)
Cyantraniliprole (NL)
Cyfluthrin (NL)
Cypermethrin (NL)
Diflubenzuron (N)
Dinotefuran (NL)
Fenazaquin (NL)
Flonicamid+cyclaniliprole (N)
Tau-fluvalinate (NL)
Gamma-cyhalothrin (L)
Horticultural Oil (L)
Imidacloprid (L)
Insecticidal Soap (NL)
Isaria (paecilomyces) fumosoroseus (NL)
Lambda-cyhalothrin (L)
Malathion (L)
Metarhizum anisopliae (robertii) (NL)
Neem oil (NL)
Permethrin (NL)
Pymetrozine (NL)
Pyrethrins+piperonyl butoxide (L)
Pyrethrin+sulfur (NL)
Pyridaben (NL)
Pyriproxyfen (L)
Spinetoram+sulfoxaflor (N)
Spiromesifen (L)
Active ingredients that may be applied systemically include: Abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniprole (soil injection, soil drench), diflubenzuron (soil drench), dinotefuran (soil drench), imidacloprid (soil drench), Metarhizum anisopliae (robertii) (soil drench), and neem oil (soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
