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Home , Aleurocanthus woglumi, Mealybug, Trialeurodes, Whitefly

E-432

Whiteflies Carlos E. Bográn and Kevin M. Heinz*

can move and disperse over long distances by flying lthough there are approximately 1,200 upward and being picked up and carried by air cur- of worldwide, only a few species are rents. Eggs are usually laid on the underside of young Aof economic importance. Most species leaves and may be deposited randomly throughout have a narrow range of host plants, but the ones that the leaf, in circles, arcs or spirals, depending on the are considered pests may feed on and damage many species. vegetable and field crops, greenhouse and nursery The eggs hatch into mobile first called crops and house plants. crawlers, which search and find a suitable feeding The name whitefly is site. They then insert their mouthparts and remain in derived from the generally one place for the rest of their immature stages. white, wax-like substance that Second to fourth instars are called nymphs and coats their bodies, particularly resemble small scale . Nymphs are oval and the wings. Some species are may be pale yellow to black, depending on the dark with colored wing pat- species. The late fourth is also known as “” Bastiaan Drees, TAMU terns. All developmental stages because mobile adults emerge from the exoskeleton of secrete wax, and in nymphs (immatures), the appear- sessile nymphs after development is complete. ance of accumulated wax filaments and plates is used fourth instars are also known as in species identification. “red-eye nymphs” because the relatively large eyes of The main whitefly species that feed on ornamental the developing adult are already visible through the plants in Texas are the silverleaf whitefly ( integument (skin) during this stage. argentifolii [Bellows & Perring]), the greenhouse white- The complete life cycle varies from about 21/2 to 5 fly ( vaporariorum [Westwood]) and the weeks according to temperature conditions and banded wing whitefly ( species. Many overlapping generations can occur each [Haldeman]). Other species include the blackfly year. Adults and nymphs feed by inserting their ( woglumi Ashby), the citrus whitefly mouthparts into plant tissue and sucking phloem sap. ( citri Ashmead) and the giant whitefly ( dugesii Cockerell). It is important to dis- Silverleaf Whitefly tinguish the different whiteflies because damage The silverleaf whitefly is the potential and susceptibility to control differs by most economically important species. whitefly species in Texas. Adults are 0.8-1.2 millimeter long with Description and iLfe Cycle white wings (without markings) Carlos Bogran, TAMU and pale yellow bodies. The wings are held in a roof- Whiteflies are small insects (1 to 3 millimeter). like position (about a 45-degree angle) over their bod- Adults have four broad wings of approximately the ies, whereas other whiteflies typically hold the wings same size. The adult is the most mobile stage and is nearly flat when at rest. As a result, the silverleaf responsible for colonizing the host plant. Whiteflies whitefly appears more slender than other common whiteflies. Eggs are oblong, smooth and yellow to *Assistant Professor & Extension Specialist and Associate Professor of Entomology, The Texas A&M University System amber brown and are laid randomly on the underside of leaves. Nymphs are greenish-yellow, oval and flat. color. Adult citrus blackflies are 1.3-1.6 millimeter Late third and fourth instars develop distinctive eye long with slate-blue wings and red abdomens. spots and are often referred to as red-eyed nymphs. Females lay eggs in a characteristic spiral pattern. Silverleaf whitefly pupae are oval, flattened (with Nymphs and pupae are dark black, with a fringe of tapering sides) and lack the marginal fringe of wax fil- white wax filaments along the upper perimeter. aments common to other whiteflies. Their hosts Citrus whiteflies are an occasional of citrus in include more than 500 species representing 74 plant southern Texas but may also attack ornamental plants families. and trees such as Boston ivy, chinaberry, laurel cher- ry, crepe myrtle, English ivy, , green ash, jas- mine, osage orange, prickly ash, trumpet vine, water This is an occasional pest, oak, persimmon and wild olive. Adults are very simi- especially in greenhouses. lar to adult greenhouse whiteflies but have broader Adults are about the same size wings and feed mainly on shrubs and trees, especially as the silverleaf whitefly (0.9- citrus. Nymphs and pupae are similar to those of the 1.1 millimeter). The wings are silverleaf whitefly but are much rounder in shape. held nearly parallel to the leaf Michael Parrella, U. California and cover the abdomen when Davis Giant whitefly adults are about three times larger at rest. Eggs are occasionally laid in circular patterns than other common whiteflies. Wings overlap when on plants with smooth leaves. Eggs are oblong, at rest and are mottled with grey markings. Common smooth and are initially yellow but darken before hosts include bamboo, begonia, bird of paradise, cit- hatching. Pupae are oval, slightly raised (with vertical rus, geranium, , ivy, jasmine, morning glory, sides) and have a fringe of wax filaments along the lantana, passion flower, philodendron and pittospori- perimeter of their upper surface. Relatively large wax um. Nymphs and pupae secrete long cylindrical filaments project from their bodies; the number and strands of wax extending up to two inches (50 mil- length of these filaments varies with the host plant. limeters) from the leaf surface. Accumulation of these Their hosts include more than 200 plant species. wax strands resembles fluffy-white hair. Females deposit eggs and wax in spiral patterns that appear as Bandedwinged Whitefly white concentric circles on the undersides of host This is an occasional pest of plant leaves. crops and ornamental plants, especially hibiscus. The adults are slightly larger than silver- Damage leaf and greenhouse whiteflies. Whiteflies can damage plants directly or indirectly. They can be recognized by two Carlos Bogran. TAMU Direct damage is caused through their feeding, which irregularly shaped (in zig-zag removes plant sap and stunts plant growth, especially pattern) gray bands on the front pair of wings. Except in young plants. Silverleaf whitefly feeding has been for these banded front wings, the adults are very simi- associated with several plant disorders, including sil- lar in size and shape to adult greenhouse whiteflies. verleaf of squash, stem blanching and whitening of poinsettia and cruciferous vegetables, and irregular The eggs are oblong and smooth and may be laid ripening of tomatoes. Indirect whitefly damage is irregularly or in neat circles on the leaves, depending caused by the large amounts of sticky on the host plant species. Eggs are pale yellow and secreted during feeding. Honeydew may cover plants turn pink before hatching. Pupae are oval, slightly and support the growth of sooty mold, which reduces raised (with vertical sides) and have a fringe of wax the plant’s ability to use light filaments along the upper perimeter. Pupae have a for . In addition dark area in the upper surface of the integument, to direct and indirect damage, which distinguishes them from the pupae of green- whiteflies may carry and trans- house whiteflies. Important ornamental hosts include mit viral diseases that can poinsettia, geranium, hibiscus and petunia. severely damage susceptible Bastiaan Drees, TAMU Other Whitefly Species plants. The citrus blackfly is a spo- radic pest of ornamental plants and a potentially serious pest of citrus, especially in South Texas. Both nymphs and adults are easily distinguished from other Bastiaan Drees, TAMU whitefly species by their dark

2 Break the whitefly reproductive cycle by having Integrated Pest Management periods of time with no host plants in the green- Integrated pest management (IPM) is a strategy to house or garden. avoid or prevent pest damage with minimum adverse impact to human health, environment and non-target organisms. Successful IPM of whiteflies involves: Pest Monitoring and Implementing cultural control practices to limit Diagnosis whitefly colonization. Whiteflies, like many other pests, reproduce very Frequent monitoring of populations. rapidly. A single female may lay 150-300 eggs during her lifetime. When temperatures are high at the peak Accurate species identification and pest diagno- of summer, whiteflies may complete development in sis to select proper control action. 16-18 days. In the absence of natural enemies and Using pertinent information to decide when other natural control factors such as heavy rain, a few treatment is necessary. individuals can produce thousands in a very short time. Therefore, it is important to monitor plants fre- Using effective pest management tools, including quently. Do not wait until damage is obvious because tolerant species or varieties (when available), whitefly control is very difficult to achieve at that natural enemies and . point. Inspect the undersides of old and new leaves weekly for all whitefly stages. The more plants you inspect, the more likely you will be to detect prob- Cultural Control lems sooner, when management is easier. Record the Cultural control practices are number of whiteflies per plant or the percentage of aimed at avoiding or preventing plants infested. This information is critical in deciding whitefly infestations, eliminat- whether or not treatment is necessary. ing sources of whiteflies and keeping whiteflies out of grow- Although yellow sticky traps sold at garden stores ing areas. To implement cultur- Bastiaan Drees, TAMU may be used to detect when and where whitefly al control you should: adults are occurring, they are not useful in estimating population density on plants. They should be placed Thoroughly inspect new plants before purchase just above the plant canopy and must be checked and and reject or treat any infested material. replaced every week. Make sure the plants are free of whiteflies Once you have detected whiteflies on plants, accu- before putting them with established plants. rate species identification is essential in deciding Keep target areas free of weeds that can serve as whether or not further action is required and what whitefly hosts. treatment to use. Learn the different species of white- flies that commonly attack the plants you are trying When feasible, avoid growing susceptible plants to protect and the natural enemies of whiteflies that of different ages together in one place or imme- may be common in your area. Use a magnifying lens diately replanting after harvest when pests from (10X) to facilitate observation. a previous crop may still be present. Silverleaf whiteflies and, occasionally, greenhouse Avoid excess irrigation and fertilization, which whiteflies may cause serious damage to plants. may increase the susceptibility of plants to Managing these species may be very difficult if popu- whiteflies. lations are not detected early. Bandedwinged white- Avoid planting when whiteflies are expected to flies will feed on several weeds and ornamental plants migrate from other hosts. Whiteflies migrate but will reproduce on only a few of them. Manage- from alternate hosts because numbers have ment may be necessary only on plants that harbor become too high or the crop is being harvested eggs and nymphs. Giant whitefly adults tend to (e.g., after cotton defoliation). remain on the plant where they developed. This ten- dency leads giant whitefly populations to be initially When practical, isolate groups of plants using clustered on a few plants, which helps a grower to row covers, screens or plastic sheets. manage them. Removing and destroying relatively Remove and destroy heavily infested plants from few infested leaves may significantly reduce popula- the landscape so they will not contaminate other tions. Citrus blackfly and citrus whitefly are two plants. species that are controlled well by native and intro- duced natural enemies and generally do not require treatment. Consult your county Extension agent for additional help identifying a species.

3 have been conducted against several whitefly species Management Considerations including silverleaf whitefly, citrus whitefly, citrus A certain number of whiteflies may be tolerated blackfly and giant whitefly. when they do not cause significant damage. This tol- The purchase and release of natural enemies is also erance level varies according to the host plant and known as augmentation biological control. Augmenta- individual preferences. A few adults feeding on plants tion biological control has been effective in control- will usually not cause significant damage and do not ling whiteflies in greenhouse ornamental production. warrant treatment. However, if monitoring reveals an A list of commercial suppliers of natural enemies in increasing number of eggs and nymphs on young North America can be obtained by visiting www. leaves and the weather conditions are favorable, inter- cdpr.ca.gov/docs/ipminov/bensupp.htm. vention may be required to prevent future damage. is the most whitefly-specific Intervention may be physical/mechanical control, predator available. It feeds primarily on whitefly eggs biological control or chemical control. Physical/ but may also consume nymphs. It is particularly use- mechanical control includes removing heavily infest- ful in reducing whitefly populations in greenhouses, ed leaves or plants and using a high-pressure water although it may also be used outside. Recommended spray on the underside of leaves. Removing infested release rates are seven to ten per m2 (10 ft.2). leaves from plants may be enough to control small populations on less preferred hosts. Removing a few Eretmocerus eremicus is the most effective para- infested plants early may prevent future problems. sitoid available for biological control of silverleaf High-pressure water sprays will wash away honeydew whitefly, while formosa is effective for treat- and sooty mold accumulations and reduce popula- ing the greenhouse whitefly. are effective tions of adults and nymphs. High-pressure water at suppressing low whitefly population densities and sprays are recommended at least once a week for may prevent a pest outbreak but do not control an three consecutive weeks and can be repeated as nec- existing one. Recommended release rates in the green- essary. house vary with whitefly population density from three per 2 m2 ( 2 per 15 ft.2) every 1-2 weeks, starting at first sign of whitefly presence, to three or Biological Control more weekly introductions of three to nine wasps per Biological control is the manipulation of natural m2 (10 ft.2) when whitefly populations are initially enemies to prevent or suppress damage from pests. established, to weekly releases of one to three wasps Several species of predators and parasitoids are natur- per plant for highly susceptible crops like poinsettia. al enemies of whiteflies. Predators of whiteflies The easiest biological control method in a land- include ladybeetles (Delphastus and Nephaspis), green scape is to conserve naturally occurring predators and lacewings (Chrysopa and Chrysoperla), minute pirate parasitoids. Conservation biological control involves bugs (), big eyed bugs () and damsel bugs the careful selection and use of only when (Nabis). Parasitoids ( parasites) of whiteflies necessary to prevent pest damage. Judicious use of include minute wasps (Encarsia and Eretmocerus) insecticides not only will preserve natural enemies about 1 millimeter long and either yellow, dark but will also reduce health and environmental risks. brown or bicolor (brown head and yellow body), depending on the species. Females of these tiny, para- sitic wasps lay their eggs inside whitefly nymphs. Chemical Control When the eggs hatch, the larvae feed internally Several classes of insecticides are labeled for use on the whitefly nymphs, eventually killing them. against whiteflies on ornamental plants. Table 1 lists In addition to predators and parasitoids, whiteflies some whitefly control products available to commer- are naturally attacked by insect pathogens. Spores cial ornamental producers, and Table 2 shows prod- from the fungal pathogen , which ucts available to homeowners. Insecticidal soaps and causes white-muscardine disease in insects, have been horticultural oils are contact insecticides that cause formulated into insecticidal products (see Table 1). suffocation and desiccation of nymphs and adults. Soaps and oils are among the best alternatives for Biological control can be achieved by importing whitefly control by home owners because they are and releasing natural enemies from areas where pests effective, preserve natural enemies and are relatively originate, by purchasing and releasing commercially safe. It is important to thoroughly cover the underside available natural enemies or by conserving naturally of leaves and repeat applications. Insect growth regu- occurring ones. Importing natural enemies—also lators, when applied during the immature stages, pre- known as classical biological control—involves coordi- vent adult whitefly development. These products gen- nated efforts of university, state and federal scientists erally do not kill adult whiteflies present at the time and regulators. Classical biological control programs of a treatment.

4 To reduce the impact of insecticides on natural ene- Mention of commercial products is for educa- mies, avoid the frequent use of broad-spectrum insec- tional purposes only and does not represent ticides (those labeled against many pests) because endorsement by Texas Cooperative Extension or these also kill predators and parasitoids. Avoid fre- The Texas A&M University System. quent, long-term use of insecticides with the same label registrations are subject to change, and mode of action because this may lead to the growth of changes may have occurred since this publication populations of insects that are resistant to the chemi- was printed. The user is always responsi- cals. Insects that are resistant to one insecticide may ble for applying products in accordance with label also be resistant to other insecticides (cross-resis- directions. Always read and carefully follow the tance). instructions on the container label. Under certain temperature, humidity, water and shade conditions, pesticides may also cause injury to For information on whitefly pest management on certain plants (phytotoxicity). Generally, apply pesti- vegetable gardens and citrus, see Extension publica- cides during early morning or late afternoon to avoid tion B-1300. For more information on Texas insects the hottest part of the day. Water plants 1-2 days and entomology, see http://insects.tamu.edu. before applying pesticide. Always check the product label for the list of plants that may be injured by the pesticide.

5 Table 1. Insecticidal products to control whiteflies on commercial ornamental production (always read and follow directions printed on label; some products may have restrictions) Insecticide REI2 Type/Source (Commercial Name) Site Use1 (hours) Notes Biological Beauveria bassiana L, GH, N 4 Repeated applications are necessary. (BotaniGard®; Naturalis®) Do not mix with most fungicides. Fungicide applications may affect efficacy Oil Horticultural oil (SunSpray L, GH, N 4 Do not use with sulfur fungicides Ultra-Fine Spray Oil®) Oil Clarified hydrophobic extract L, GH, N 4 Check label for list of plants that may of neem oil (Triact®) be treated. Some products also act as fungicides Soap Potash soap (Safer- Contact with insect and repeated ®, M-Pede®) L, GH, N 4 - 12 applications are necessary Botanical Pyrethrin + PBO (Pyrenone L, GH, N 12 PBO is piperonyl butoxide, a Crop Spray®) synergist Botanical Pyrethrin + rotenone GH, N 12 (Pyrellin®) Fermentation Abamectin (Avid®) GH, N 12 Commercial use only Product Chloronicotinyl (Marathon®, L, GH, N 12 Use only once every 16 weeks Merit®) Pyridazinone Pyridaben (Sanmite®) GH, N 12 Contact with insect required Pyridine-azomethine Pymetrozine (Endeavor™) L, GH, N 12 Insect Growth Azadirachtin (Azatin XL®, L, GH, N 4 Contact with insect and repeated Regulator Safer BioNeem®) applications are necessary Insect Growth Diflubenzuron (Adept®) GH 12 Contact with insect and weekly Regulator applications are necessary Insect Growth Kinoprene (Enstar®) GH 4 Apply before bloom Regulator Insect Growth Fenoxycarb (Precision®) L, GH, N 12 Max 30 applications per year in Regulator greenhouses Insect Growth (Distance®, L, GH, N 12 Apply no more than two times per Regulator Pyrigro®) cropping cycle or no more than two times per 6 months (Talstar®, Orthro® L, GH, N 12 products) Pyrethroid Cyfluthrin (Decathlon®, L, GH, N 12 Tempo®) Pyrethroid Fenpropathrin (Tame®) L, GH, N 24 Restricted use product Pyrethroid Fluvalinate (Mavrik®) L, GH, N 12 Pyrethroid (Astro®) L, GH, N 12 Organophosphate Acephate (Orthene® Turf, L, GH, N 12 Can affect growth of new roses Tree & Ornamental Spray) (KnoxOut®) L, N 12 Malathion (various products) L, GH, N 12 1GH, N, L represent approved site use; L = landscape, GH = greenhouse, and N= nursery. 2REI = restricted entry interval (consult product label).

6 Table 2. Homeowner packaged whitefly control products (always read and follow directions printed on label) Type/Source Insecticide (Commercial Name) Notes Oil Horticultural oil (SunSpray Ultra-Fine Spray Oil®, Do not use with sulfur fungicides Volck® Oil Spray, Dexol® Dormant and Summer Oil Spray) Oil Clarified hydrophobic extract of neem oil Check label for list of plants that (Greenlight™ Neem Concentrate) may be treated. Some products also act as fungicides Soap Potash soap (Safer® Insecticidal Soap Insect Contact with insect and repeated Killer, Concern® Insect Killing Soap, Ortho® applications are necessary Insecticidal Soap®) Botanical Pyrethrum (X-Clude Pyrethrum®) Botanical Pyrethrin + PBO (Spectricide® Houseplant & PBO is piperonyl butoxide, a Garden Spray, Ortho® Rose & Flower Insect synergist Killer, Schultz™ Instant House Plant Insect Spray) Botanical + Soap Pyrethrum + potash soap (Safer® Houseplant Insect Killer®) Chloronicotinyls Imidacloprid (Bayer® Advanced Garden™ Rose & Flower Insect Killer) Insect Growth Regulator Azadirachtin ( Safer® BioNeem) Contact with insect and repeated applications are necessary Pyrethroid Bifenthrin (Orthro® products) Pyrethroid Cyfluthrin (Decathlon®, Powerforce Muti-Insect Killer®) Pyrethroid Permethrin (Spectricide® Lawn &Garden Insect Control) Pyrethroid Resmethrin (Dragon® Whitefly & Spray) Organophosphate Acephate (Orthene®; Isotox® Insect Killer) Can affect growth of new roses Diazinon (Ortho® Diazinon Plus Insect Spray, Dexol® Diazinon 25% Spray, Spectricide® Diazinon Multi-purpose Insect Spray Concentrate) Disulfoton (DiSyston®) Malathion (various products)

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