White flies

E-432

Carlos E. Bográn and Kevin M. Heinz*

Although there are approximately 1,200 speciesof whiteflies worldwide, only a few species areof economic importance. Most whitefly species

have a narrow range of host plants, but the ones thatare considered pests may feed on and damage manyvegetable and field crops, greenhouse and nurserycrops and house plants.

The name whitefly isderived from the generallywhite, wax-like substance thatcoats their bodies, particularlythe wings. Some species aredark with colored wing pat-

terns. All developmental stagessecrete wax, and in nymphs (immatures), the appear-ance of accumulated wax filaments and plates is usedin species identification.

The main whitefly species that feed on ornamentalplants in Texas are the silverleaf whitefly (Bemisiaargentifolii [Bellows & Perring]), the greenhouse white-fly (Trialeurodes vaporariorum [Westwood]) and thebanded wing whitefly (Trialeurodes abutiloneus[Haldeman]). Other species include the citrus blackfly(Aleurocanthus woglumi Ashby), the citrus whitefly(Dialeurodes citri Ashmead) and the giant whitefly(Aleurodicus dugesii Cockerell). It is important to dis-tinguish the different whiteflies because damagepotential and susceptibility to control differs byspecies.

Description and Life Cycl eWhiteflies are small insects (1 to 3 millimeter).

Adults have four broad wings of approximately thesame size. The adult is the most mobile stage and isresponsible for colonizing the host plant. Whiteflies

can move and disperse over long distances by flyingupward and being picked up and carried by air cur-rents. Eggs are usually laid on the underside of youngleaves and may be deposited randomly throughoutthe leaf, in circles, arcs or spirals, depending on thespecies.

The eggs hatch into mobile first instars calledcrawlers, which search and find a suitable feedingsite. They then insert their mouthparts and remain inone place for the rest of their immature stages.

Second to fourth instars are called nymphs andresemble small scale insects. Nymphs are oval andmay be pale yellow to black, depending on thespecies. The late fourth instar is also known as “pupa”because mobile adults emerge from the exoskeleton ofsessile nymphs after development is complete.Silverleaf whitefly fourth instars are also known as“red-eye nymphs” because the relatively large eyes ofthe developing adult are already visible through thenymph integument (skin) during this stage.

The complete life cycle varies from about 21/2 to 5weeks according to temperature conditions andspecies. Many overlapping generations can occur eachyear. Adults and nymphs feed by inserting theirmouthparts into plant tissue and sucking phloem sap.

Silverleaf Whitefly The silverleaf whitefly is the

most economically importantwhitefly species in Texas. Adultsare 0.8-1.2 millimeter long withwhite wings (without markings)and pale yellow bodies. The wings are held in a roof-like position (about a 45-degree angle) over their bod-ies, whereas other whiteflies typically hold the wingsnearly flat when at rest. As a result, the silverleafwhitefly appears more slender than other commonwhiteflies. Eggs are oblong, smooth and yellow toamber brown and are laid randomly on the underside

*Assistant Professor & Extension Specialist and Associate Professorof Entomology, The Texas A&M University System

Bastiaan Drees, TAMU

Carlos Bogran, TAMU

of leaves. Nymphs are greenish-yellow, oval and flat.Late third and fourth instars develop distinctive eyespots and are often referred to as red-eyed nymphs.Silverleaf whitefly pupae are oval, flattened (withtapering sides) and lack the marginal fringe of wax fil-aments common to other whiteflies. Their hostsinclude more than 500 species representing 74 plantfamilies.

Greenhouse Whitefly This is an occasional pest,

especially in greenhouses.Adults are about the same sizeas the silverleaf whitefly (0.9-1.1 millimeter). The wings areheld nearly parallel to the leafand cover the abdomen whenat rest. Eggs are occasionally laid in circular patternson plants with smooth leaves. Eggs are oblong,smooth and are initially yellow but darken beforehatching. Pupae are oval, slightly raised (with verticalsides) and have a fringe of wax filaments along theperimeter of their upper surface. Relatively large waxfilaments project from their bodies; the number andlength of these filaments varies with the host plant.Their hosts include more than 200 plant species.

Bandedwinged Whitefly This is an occasional pest of

crops and ornamental plants,especially hibiscus. The adultsare slightly larger than silver-leaf and greenhouse whiteflies.They can be recognized by twoirregularly shaped (in zig-zagpattern) gray bands on the front pair of wings. Exceptfor these banded front wings, the adults are very simi-lar in size and shape to adult greenhouse whiteflies.

The eggs are oblong and smooth and may be laidirregularly or in neat circles on the leaves, dependingon the host plant species. Eggs are pale yellow andturn pink before hatching. Pupae are oval, slightlyraised (with vertical sides) and have a fringe of waxfilaments along the upper perimeter. Pupae have adark area in the upper surface of the integument,which distinguishes them from the pupae of green-house whiteflies. Important ornamental hosts includepoinsettia, geranium, hibiscus and petunia.

Other Whitefly SpeciesThe citrus blackfly is a spo-

radic pest of ornamental plantsand a potentially serious pest ofcitrus, especially in South Texas.Both nymphs and adults areeasily distinguished from otherwhitefly species by their dark

color. Adult citrus blackflies are 1.3-1.6 millimeterlong with slate-blue wings and red abdomens.Females lay eggs in a characteristic spiral pattern.Nymphs and pupae are dark black, with a fringe ofwhite wax filaments along the upper perimeter.

Citrus whiteflies are an occasional pest of citrus insouthern Texas but may also attack ornamental plantsand trees such as Boston ivy, chinaberry, laurel cher-ry, crepe myrtle, English ivy, gardenia, green ash, jas-mine, osage orange, prickly ash, trumpet vine, wateroak, persimmon and wild olive. Adults are very simi-lar to adult greenhouse whiteflies but have broaderwings and feed mainly on shrubs and trees, especiallycitrus. Nymphs and pupae are similar to those of thesilverleaf whitefly but are much rounder in shape.

Giant whitefly adults are about three times largerthan other common whiteflies. Wings overlap whenat rest and are mottled with grey markings. Commonhosts include bamboo, begonia, bird of paradise, cit-rus, geranium, hibiscus, ivy, jasmine, morning glory,lantana, passion flower, philodendron and pittospori-um. Nymphs and pupae secrete long cylindricalstrands of wax extending up to two inches (50 mil-limeters) from the leaf surface. Accumulation of thesewax strands resembles fluffy-white hair. Femalesdeposit eggs and wax in spiral patterns that appear aswhite concentric circles on the undersides of hostplant leaves.

DamageWhiteflies can damage plants directly or indirectly.

Direct damage is caused through their feeding, whichremoves plant sap and stunts plant growth, especiallyin young plants. Silverleaf whitefly feeding has beenassociated with several plant disorders, including sil-verleaf of squash, stem blanching and whitening ofpoinsettia and cruciferous vegetables, and irregularripening of tomatoes. Indirect whitefly damage iscaused by the large amounts of sticky honeydewsecreted during feeding. Honeydew may cover plantsand support the growth of sooty mold, which reducesthe plant’s ability to use lightfor photosynthesis. In additionto direct and indirect damage,whiteflies may carry and trans-mit viral diseases that canseverely damage susceptibleplants.

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Michael Parrella, U. CaliforniaDavis

Carlos Bogran. TAMU

Bastiaan Drees, TAMU

Bastiaan Drees, TAMU

I nte grated Pe st ManagementIntegrated pest management (IPM) is a strategy to

avoid or prevent pest damage with minimum adverseimpact to human health, environment and non-targetorganisms. Successful IPM of whiteflies involves:

� Implementing cultural control practices to limitwhitefly colonization.

� Frequent monitoring of populations.

� Accurate species identification and pest diagno-sis to select proper control action.

� Using pertinent information to decide whentreatment is necessary.

� Using effective pest management tools, includingtolerant species or varieties (when available),natural enemies and insecticides.

Cultural Co ntrol Cultural control practices are

aimed at avoiding or preventingwhitefly infestations, eliminat-ing sources of whiteflies andkeeping whiteflies out of grow-ing areas. To implement cultur-al control you should:

� Thoroughly inspect new plants before purchaseand reject or treat any infested material.

� Make sure the plants are free of whitefliesbefore putting them with established plants.

� Keep target areas free of weeds that can serve aswhitefly hosts.

� When feasible, avoid growing susceptible plantsof different ages together in one place or imme-diately replanting after harvest when pests froma previous crop may still be present.

� Avoid excess irrigation and fertilization, whichmay increase the susceptibility of plants towhiteflies.

� Avoid planting when whiteflies are expected tomigrate from other hosts. Whiteflies migratefrom alternate hosts because numbers havebecome too high or the crop is being harvested(e.g., after cotton defoliation).

� When practical, isolate groups of plants usingrow covers, screens or plastic sheets.

� Remove and destroy heavily infested plants fromthe landscape so they will not contaminate otherplants.

� Break the whitefly reproductive cycle by havingperiods of time with no host plants in the green-house or garden.

Pe st Monito ring andDiagnosis

Whiteflies, like many other pests, reproduce veryrapidly. A single female may lay 150-300 eggs duringher lifetime. When temperatures are high at the peakof summer, whiteflies may complete development in16-18 days. In the absence of natural enemies andother natural control factors such as heavy rain, a fewindividuals can produce thousands in a very shorttime. Therefore, it is important to monitor plants fre-quently. Do not wait until damage is obvious becausewhitefly control is very difficult to achieve at thatpoint. Inspect the undersides of old and new leavesweekly for all whitefly stages. The more plants youinspect, the more likely you will be to detect prob-lems sooner, when management is easier. Record thenumber of whiteflies per plant or the percentage ofplants infested. This information is critical in decidingwhether or not treatment is necessary.

Although yellow sticky traps sold at garden storesmay be used to detect when and where whiteflyadults are occurring, they are not useful in estimatingpopulation density on plants. They should be placedjust above the plant canopy and must be checked andreplaced every week.

Once you have detected whiteflies on plants, accu-rate species identification is essential in decidingwhether or not further action is required and whattreatment to use. Learn the different species of white-flies that commonly attack the plants you are tryingto protect and the natural enemies of whiteflies thatmay be common in your area. Use a magnifying lens(10X) to facilitate observation.

Silverleaf whiteflies and, occasionally, greenhousewhiteflies may cause serious damage to plants.Managing these species may be very difficult if popu-lations are not detected early. Bandedwinged white-flies will feed on several weeds and ornamental plantsbut will reproduce on only a few of them. Manage-ment may be necessary only on plants that harboreggs and nymphs. Giant whitefly adults tend toremain on the plant where they developed. This ten-dency leads giant whitefly populations to be initiallyclustered on a few plants, which helps a grower tomanage them. Removing and destroying relativelyfew infested leaves may significantly reduce popula-tions. Citrus blackfly and citrus whitefly are twospecies that are controlled well by native and intro-duced natural enemies and generally do not requiretreatment. Consult your county Extension agent foradditional help identifying a species.

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Bastiaan Drees, TAMU

Management ConsiderationsA certain number of whiteflies may be tolerated

when they do not cause significant damage. This tol-erance level varies according to the host plant andindividual preferences. A few adults feeding on plantswill usually not cause significant damage and do notwarrant treatment. However, if monitoring reveals anincreasing number of eggs and nymphs on youngleaves and the weather conditions are favorable, inter-vention may be required to prevent future damage.

Intervention may be physical/mechanical control,biological control or chemical control. Physical/mechanical control includes removing heavily infest-ed leaves or plants and using a high-pressure waterspray on the underside of leaves. Removing infestedleaves from plants may be enough to control smallpopulations on less preferred hosts. Removing a fewinfested plants early may prevent future problems.High-pressure water sprays will wash away honeydewand sooty mold accumulations and reduce popula-tions of adults and nymphs. High-pressure watersprays are recommended at least once a week forthree consecutive weeks and can be repeated as nec-essary.

Biological Co ntro lBiological control is the manipulation of natural

enemies to prevent or suppress damage from pests.Several species of predators and parasitoids are natur-al enemies of whiteflies. Predators of whitefliesinclude ladybeetles (Delphastus and Nephaspis), greenlacewings (Chrysopa and Chrysoperla), minute piratebugs (Orius), big eyed bugs (Geocoris) and damsel bugs(Nabis). Parasitoids (insect parasites) of whitefliesinclude minute wasps (Encarsia and Eretmocerus)about 1 millimeter long and either yellow, darkbrown or bicolor (brown head and yellow body),depending on the species. Females of these tiny, para-sitic wasps lay their eggs inside whitefly nymphs.When the wasp eggs hatch, the larvae feed internallyon the whitefly nymphs, eventually killing them.

In addition to predators and parasitoids, whitefliesare naturally attacked by insect pathogens. Sporesfrom the fungal pathogen Beauveria bassiana, whichcauses white-muscardine disease in insects, have beenformulated into insecticidal products (see Table 1).

Biological control can be achieved by importingand releasing natural enemies from areas where pestsoriginate, by purchasing and releasing commerciallyavailable natural enemies or by conserving naturallyoccurring ones. Importing natural enemies—alsoknown as classical biological control—involves coordi-nated efforts of university, state and federal scientistsand regulators. Classical biological control programs

have been conducted against several whitefly speciesincluding silverleaf whitefly, citrus whitefly, citrusblackfly and giant whitefly.

The purchase and release of natural enemies is alsoknown as augmentation biological control. Augmenta-tion biological control has been effective in control-ling whiteflies in greenhouse ornamental production.A list of commercial suppliers of natural enemies inNorth America can be obtained by visiting www.cdpr.ca.gov/docs/ipminov/bensupp.htm.

Delphastus pusillus is the most whitefly-specificpredator available. It feeds primarily on whitefly eggsbut may also consume nymphs. It is particularly use-ful in reducing whitefly populations in greenhouses,although it may also be used outside. Recommendedrelease rates are seven to ten per m2 (10 ft.2).

Eretmocerus eremicus is the most effective para-sitoid available for biological control of silverleafwhitefly, while Encarsia formosa is effective for treat-ing the greenhouse whitefly. Parasitoids are effectiveat suppressing low whitefly population densities andmay prevent a pest outbreak but do not control anexisting one. Recommended release rates in the green-house vary with whitefly population density fromthree wasps per 2 m2 ( 2 per 15 ft.2) every 1-2 weeks,starting at first sign of whitefly presence, to three ormore weekly introductions of three to nine wasps perm2 (10 ft.2) when whitefly populations are initiallyestablished, to weekly releases of one to three waspsper plant for highly susceptible crops like poinsettia.

The easiest biological control method in a land-scape is to conserve naturally occurring predators andparasitoids. Conservation biological control involvesthe careful selection and use of pesticides only whennecessary to prevent pest damage. Judicious use ofinsecticides not only will preserve natural enemiesbut will also reduce health and environmental risks.

Chemical Co ntro lSeveral classes of insecticides are labeled for use

against whiteflies on ornamental plants. Table 1 listssome whitefly control products available to commer-cial ornamental producers, and Table 2 shows prod-ucts available to homeowners. Insecticidal soaps andhorticultural oils are contact insecticides that causesuffocation and desiccation of nymphs and adults.Soaps and oils are among the best alternatives forwhitefly control by home owners because they areeffective, preserve natural enemies and are relativelysafe. It is important to thoroughly cover the undersideof leaves and repeat applications. Insect growth regu-lators, when applied during the immature stages, pre-vent adult whitefly development. These products gen-erally do not kill adult whiteflies present at the timeof a treatment.

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To reduce the impact of insecticides on natural ene-mies, avoid the frequent use of broad-spectrum insec-ticides (those labeled against many pests) becausethese also kill predators and parasitoids. Avoid fre-quent, long-term use of insecticides with the samemode of action because this may lead to the growth ofpopulations of insects that are resistant to the chemi-cals. Insects that are resistant to one insecticide mayalso be resistant to other insecticides (cross-resis-tance).

Under certain temperature, humidity, water andshade conditions, pesticides may also cause injury tocertain plants (phytotoxicity). Generally, apply pesti-cides during early morning or late afternoon to avoidthe hottest part of the day. Water plants 1-2 daysbefore applying pesticide. Always check the productlabel for the list of plants that may be injured by thepesticide.

For information on whitefly pest management onvegetable gardens and citrus, see Extension publica-tion B-1300. For more information on Texas insectsand entomology, see http://insects.tamu.edu.

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Mention of commercial products is for educa-tional purposes only and does not representendorsement by Texas Cooperative Extension orThe Texas A&M University System. Insecticidelabel registrations are subject to change, andchanges may have occurred since this publicationwas printed. The pesticide user is always responsi-ble for applying products in accordance with labeldirections. Always read and carefully follow theinstructions on the container label.

Table 1. Insecticidal products to control whiteflies on commercial ornamental production (always read andfollow directions printed on label; some products may have restrictions)

Insecticide REI2Type/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 fungicidesUltra-Fine Spray Oil®)

Oil Clarified hydrophobic extract L, GH, N 4 Check label for list of plants that mayof neem oil (Triact®) be treated. Some products also act

as fungicidesSoap Potash soap (Safer- Contact with insect and repeated

Insecticidal Soap®, M-Pede®) L, GH, N 4 - 12 applications are necessaryBotanical Pyrethrin + PBO (Pyrenone L, GH, N 12 PBO is piperonyl butoxide, a

Crop Spray®) synergistBotanical Pyrethrin + rotenone GH, N 12

(Pyrellin®)Fermentation Abamectin (Avid®) GH, N 12 Commercial use onlyProductChloronicotinyl Imidacloprid (Marathon®, L, GH, N 12 Use only once every 16 weeks

Merit®)Pyridazinone Pyridaben (Sanmite®) GH, N 12 Contact with insect requiredPyridine-azomethine Pymetrozine (Endeavor™) L, GH, N 12Insect Growth Azadirachtin (Azatin XL®, L, GH, N 4 Contact with insect and repeatedRegulator Safer BioNeem®) applications are necessary Insect Growth Diflubenzuron (Adept®) GH 12 Contact with insect and weeklyRegulator applications are necessaryInsect Growth Kinoprene (Enstar®) GH 4 Apply before bloomRegulatorInsect Growth Fenoxycarb (Precision®) L, GH, N 12 Max 30 applications per year inRegulator greenhousesInsect Growth Pyriproxyfen (Distance®, L, GH, N 12 Apply no more than two times per Regulator Pyrigro®) cropping cycle or no more than two

times per 6 monthsPyrethroid Bifenthrin (Talstar®, Orthro® L, GH, N 12

products)Pyrethroid Cyfluthrin (Decathlon®, L, GH, N 12

Tempo®)Pyrethroid Fenpropathrin (Tame®) L, GH, N 24 Restricted use productPyrethroid Fluvalinate (Mavrik®) L, GH, N 12Pyrethroid Permethrin (Astro®) L, GH, N 12Organophosphate Acephate (Orthene® Turf, L, GH, N 12 Can affect growth of new roses

Tree & Ornamental Spray)Diazinon (KnoxOut®) L, N 12Malathion (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).

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Table 2. Homeowner packaged whitefly control products (always read and follow directions printed onlabel)

Type/Source Insecticide (Commercial Name) Notes

Oil Horticultural oil (SunSpray Ultra-Fine Spray Oil®, Do not use with sulfur fungicidesVolck® 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 fungicidesSoap Potash soap (Safer® Insecticidal Soap Insect Contact with insect and repeated

Killer, Concern® Insect Killing Soap, Ortho® applications are necessaryInsecticidal Soap®)

Botanical Pyrethrum (X-Clude Pyrethrum®)Botanical Pyrethrin + PBO (Spectricide® Houseplant & PBO is piperonyl butoxide, a

Garden Spray, Ortho® Rose & Flower Insect synergistKiller, 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 & Mealybug 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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