Whiteflies are a common pest of many ornamental plants throughout Florida and the world. There are more than 1,500 species worldwide and over 75 reported in Florida. Some of the most economically important species in Florida are the sweetpotato whitefly, also called the silverleaf whitefly (Bemisia tabaci) (Figure 1), the ficus whitefly (Singhiella simplex) (Figure 2), and the citrus whitefly (Dialeurodes citri) (Figure 3). Although infestation does not always require treatment, it is important to be able to identify and monitor for these pests for effective integrated pest management (IPM).
A generalized life cycle of the whitefly is as follows: The eggs are laid on the undersides of the leaves and hatch in 4 to 12 days into active, six-legged nymphs (crawlers). The crawlers move around for several hours, then insert their mouthparts into the leaves and stay there. After molting three times, they pupate and then become adults. The pupal case remains on the plant tissue even after the adult has emerged. How long it takes for the insects to develop from eggs to adults varies from 4 weeks (summer) to 6 months (winter).
Whiteflies have piercing-sucking (needle-like) mouthparts with which they puncture the leaf and suck the plant fluids. The top sides of leaves on infested plants become pale or spotted due to these insects feeding on the undersides of the leaves. Oftentimes an infestation goes unnoticed until leaves turn yellow or drop unexpectedly, or until an infested plant is disturbed and small clouds of whiteflies emerge from it. Some whitefly species can cause greater damage by transmitting plant viruses.
Whiteflies (as well as soft scales, mealybugs, and aphids) excrete a sugary substance called honeydew, and an unsightly black fungus called sooty mold grows on the honeydew. Besides being unattractive, sooty mold may interfere with photosynthesis, reduce plant growth, and cause early leaf drop. Sooty mold usually weathers away after an insect infestation is controlled. Ants also feed on the honeydew, so if ants become a problem, plants should be examined closely for these sucking pests.
Whiteflies are small, winged insects that resemble small moths and are covered by white waxy powder (Figure 4). Despite their name and appearance, whiteflies are neither moths nor flies, but true bugs more closely related to aphids and scale insects. Whiteflies have hair-like, piercing-sucking mouthparts that extract nutrients from plant tissue.
Most individuals are 1/16 inch (1.6 mm) long and have four wings. The most accurate method of identification is with a microscope using the final instar immature stage (nymph) or "pupa" (Figure 5). However, this is often not possible or unrealistic under field conditions. Therefore, using a 10-40X hand lens to examine adults and pupae is the best field identification method. Whitefly nymphs typically occur on the undersides of leaves. They are flat, oval, and somewhat translucent. Some species are light green to whitish and somewhat transparent. Others, like the mulberry whitefly, are black in the center and have a white, waxy fringe around the edge (Figure 6). As the nymphs mature, they often become "plump," develop distinct eye spots, and are easier to see.
The silverleaf whitefly, B. tabaci, has multiple biotypes, or genetic variants of the same species. The most common biotypes are B-biotype and Q-biotype, which look identical and cannot be visually differentiated. Therefore, genetic analysis is required to differentiate the two. Q-biotype silverleaf whiteflies are highly prone to developing insecticide resistance. Thus, difficult-to-control populations of this species should be submitted for genetic analysis. More information on whitefly biotypes and submission of samples can be found at the following link, http://mrec.ifas.ufl.edu/lso/bemisia/DOCUMENTS/WhiteflyFS02.pdf.
Whiteflies undergo four life stages: Egg, nymph, final instar nymph or "pupa," and adult. The eggs are usually deposited on the undersides of leaves and hatch in 4 to 12 days depending on temperature. Six-legged nymphs (crawlers) emerge from eggs and are mobile for up to several hours searching for a feeding site. After settling on a feeding site, they insert their hair-like piercing-sucking mouthparts into the leaves to feed on plant sap. Subsequent nymphal stages lack functioning legs and remain in this location for the remainder of their development. They pass through four nymphal instars, and in the final nymphal stage, develop wings and other adult characters. This final stage is sometimes referred to as a "pupal" stage. This stage is when species can be most accurately identified. Next, an adult whitefly will emerge from the pupa to reproduce and lay eggs for the next generation. The pupal case remains on the plant tissue even after the adult has emerged. Development time from egg to adult varies from 4 weeks to 6 months depending on whitefly species, host plant, and environmental conditions.
The most frequently attacked perennial plants are allamanda (Allamanda spp.), avocado (Persea spp.), chinaberry (Melia azedarach), citrus (Citrus spp.), ficus (Ficus spp.), fringe tree (Chionanthus spp.), gardenia (Gardenia spp.), gumbo limbo (Bursera simaruba), hibiscus (Hibiscus spp.), ligustrum (Ligustrum spp.), mango (Mangifera spp.), persimmon (Diospyros spp.), viburnum (Viburnum spp.), and various palms. Whiteflies also attack many annual plants.
The top sides of leaves on infested plants become pale or spotted due to whiteflies feeding on the undersides and extracting chlorophyll (Figure 7). Due to their small size and obscure behavior, whitefly infestations may go unnoticed until leaves turn yellow or drop unexpectedly, or until an infested plant is disturbed and small clouds of adult whiteflies emerge from it. Heavy infestations will defoliate infested regions or the entire plant (Figure 8). Some whitefly species may also cause more severe indirect damage by transmitting plant viruses.
Whiteflies, as well as soft scales, mealybugs, and aphids, excrete a sugary substance called honeydew. This substance coats surfaces beneath the feeding site and facilitates the growth of an unsightly black fungus called sooty mold. Besides being unattractive and reducing marketability, sooty mold may reduce photosynthesis and plant growth, and cause premature leaf drop. Ants and wasps also feed on the honeydew and may serve as an indicator that a plant is infested with whiteflies or other honeydew-secreting pests.
Proper plant selection, installation, irrigation, and fertilization are critical to managing whiteflies and other piercing-sucking pests of landscape ornamentals. Many whiteflies also feed and establish on weed species and vegetable plants adjacent to ornamental plantings. Silverleaf whitefly, B. tabaci, is reported to utilize at least 80 weed species among 30 families, including but not limited to thistles, spurges, and white clover. Therefore, proper weed control can facilitate successful whitefly management on landscape ornamentals. See https://edis.ifas.ufl.edu/ep523 for ornamental plant weed management recommendations.
Like many other sap-feeding pests, whiteflies may benefit from increased nutrient content of plant vascular tissue. For example, excessive nitrogen fertilization may lead to greater nitrogen content in plant tissue, which whiteflies consume, resulting in greater reproduction and survival, and faster development. Also, drought-stressed plants often exhibit greater nitrogen and sugar concentrations in their vascular systems. Sap-feeding insects such as whiteflies feed on this tissue and may benefit from the increased nutrient content.
Whitefly eggs and nymphs are commonly preyed upon by predators including lacewings (Chrysididae), predatory bugs (Anthocoridae, Geocoridae, Reduviidae, others), beetles (Coccinellidae), and mites (Phytoseiidae). Specific examples of predators include the predatory beetle, Delphastus spp., and predatory mite, Amblyseius swirskii (Figure 9). Whitefly nymphs are also commonly parasitized by small wasps, particularly Encarsia spp.
The rugose spiraling whitefly (Aleurodicus rugioperculatus) became a damaging exotic pest of landscape ornamentals for several years following its introduction to Florida in 2009. It has since been dramatically reduced by a parasitic wasp, Encarsia noyesi (Figure 10). Citrus whitefly (Dialeurodes citri) nymphs, one of the most common whitefly species attacking ornamental plants, are also frequently parasitized by a small wasp, Prospaltella lahorensis. Natural parasitism can be monitored by looking for the presence of parasitized nymphs or pupae, which will have a round exit hole where the parasitoid emerged (Figure 11). If parasitism is evident, minimize the use of contact-toxic insecticides to facilitate natural enemies getting established and providing control.
The sweetpotato (silverleaf) whitefly, B. tabaci, replaced the citrus whitefly within the last 15–20 years as the most damaging whitefly species attacking ornamental plants. This whitefly is also frequently attacked by a suite of parasitoids, but remains difficult to control.
In greenhouse systems, whiteflies are often managed using augmentative releases of natural enemies. Predators or parasitoids are purchased from commercial insectaries and periodically released to reduce pests. This practice may not be practical in landscapes due to their open nature. Although little research has investigated this approach with whitefly management, conservation biological control may be an effective method for promoting predation and parasitism of whitefly pests in landscapes. This involves planting and maintaining flowering plants and different types of plants in the landscape that will provide natural enemies with nearby alternative food resources and habitat.
In an effective IPM program, chemical control options should not be the first approach to managing whitefly pests. Many whiteflies can be managed using proper cultural and biological control practices. Incorrect or unnecessary applications of insecticides can reduce predator and parasitoid populations, further compounding the problem. Insecticides can be grouped into compounds that are considered more compatible with natural enemies and IPM programs (e.g. low-impact, biorational, reduced-risk) or compounds that are more widely toxic and not compatible with natural enemies, such as conventional insecticides.
In many cases, foliar applications of low-impact insecticides like insecticidal soaps or horticultural oils can effectively reduce whitefly populations. Be sure to read and understand the label instructions before making an application. Thorough coverage on the undersides of the leaves is especially important. Repeat at weekly intervals until populations are reduced below damaging levels. Always consider weather conditions because intense heat and sunlight can cause severe plant damage.
Some whiteflies are naturally attacked by beneficial fungi such as Aschersonia sp. (Figure 12), and Isaria fumosorosea. Entomopathogenic fungi such as Beauvaria bassiana, Metarhizium anisopliae, and Isaria fumosorosea are sold commercially as biorational insecticides for pest management and can effectively control these pests (see table 2). Other biorational products include plant-derived toxins like azadirachtin derived from the neem tree (Azadirachta indica).
When additional or more aggressive chemical control is needed, there are several synthetic insecticides that effectively reduce whiteflies. The silverleaf whitefly, particularly Q-biotype, is especially prone to developing insecticide resistance, and multiple populations have exhibited some level of resistance to multiple insecticide classes, including neonicotinoids. Therefore, rotating chemical modes of action (IRAC numbers) in a management program is critical for prolonging successful control. It is important not only to rotate, but make sure not to apply the same mode of action to subsequent generations of the same pest population.
The United States EPA has classified several insecticides for landscape use as reduced-risk based on several metrics including low non-target toxicity, high selectivity, low use rates, and compatibility with IPM practices (for more information, see https://www.epa.gov/pesticide-registration/conventional-reduced-risk-pesticide-program). Many of these products can provide safer alternatives to other commonly used synthetic insecticides to effectively control whiteflies (see table 2).
In addition, systemic insecticides like anthranilic diamides (cyantraniliprole), neonicotinoids (e.g. imidacloprid, dinotefuran), and butenolides (flupyridifurone), as well as translaminar insecticides like insect growth regulators (e.g. buprofezin, pyriproxyfen) can provide effective whitefly management in the landscape. These products provide extended residual control, and a rotation of these classes incorporates multiple modes of action and application methods. Importantly, these products do not rely primarily on contact, are ingested by the insects feeding on plant material, and most are compatible with natural enemies compared to contact-toxic, broad spectrum insecticides. Using alternative application methods including basal trunk sprays, granular treatments, trunk injections, and soil drenches or injections can also reduce exposure of products to non-target organisms. Most of these products are unavailable for homeowner purchase and use. Thus, certified pesticide applicators may be required for application.
Broad-spectrum, contact-toxic insecticides like pyrethroids, organophosphates, or carbamates are also commonly used to manage whiteflies. These chemistries can provide a rapid reduction in abundance when whiteflies are susceptible, but may not be the most IPM-compatible choice. These products are not selective, which means they will kill natural enemies in addition to the target pests. Natural enemies should always be present in the landscape, because they provide pest control between insecticide applications. Non-selective products eliminate this advantage.
Although different insecticide groups have advantages and disadvantages, all are toxic to bees and other pollinators if the pollinators come in direct contact with the material. Therefore, they should only be used as necessary following UF/IFAS-recommended best management practices. This includes not applying products to flowering plants or when pollinators are present. Due to recent evidence and events associated with insecticides and pollinating insects, some products may become unavailable or restricted in their use to protect bees and pollinators. The benefits of these systemic products must be weighed against their effects on bees and pollinators. For more information on protecting pollinators from pesticide use, visit https://edis.ifas.ufl.edu/in1027.
Insecticides that are labeled for whitefly control by non-professionals are listed in Table 1, and professional products are listed in Table 2.
For More Information
Landscape IPM: https://edis.ifas.ufl.edu/in109
Florida Whitefly: http://www.flwhitefly.org
Solutions for Your Life: https://sfyl.ifas.ufl.edu/agriculture/whiteflies/
Fig or ficus whitefly: https://mrec.ifas.ufl.edu/lso/IAWG/FIG/The%20Fig%20Whitefly.htm
Rugose spiraling whitefly: https://edis.ifas.ufl.edu/in1015
Silverleaf whitefly (B. tabaci) information webpage: http://mrec.ifas.ufl.edu/lso/bemisia/bemisia.htm
Entomology and IPM for Foliage Plants: http://mrec.ifas.ufl.edu/LSO/Whiteflies.htm
Insecticide Resistance Action Committee Website (IRAC): http://www.irac-online.org
Insecticides labeled for non-commercial (homeowner) use against whiteflies in Florida.
Insecticides labeled for commercial use against whiteflies in Florida.