Pn White Flies

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PESTNOTES Publication 7401University of California

Agriculture and Natural Resources Revised September 2002

WHITEFLIESIntegrated Pest Management for Home Gardeners and Professional Landscapers

Whiteflies are tiny, sap-sucking insectsthat are frequently abundant in veg-etable and ornamental plantings. Theyexcrete sticky honeydew and causeyellowing or death of leaves. Out-

breaks often occur when the naturalbiological control is disrupted. Man-agement is difficult.

IDENTIFICATION ANDLIFE CYCLEWhiteflies usually occur in groups onthe undersides of leaves. They derivetheir name from the mealy, white wax

covering the adults wings and body.Adults are tiny insects with yellowish

bodies and whitish wings. Althoughadults of some species have distinctivewing markings, many species are mostreadily distinguished in the lastnymphal (immature) stage, which iswingless (Table 1).

Whiteflies develop rapidly in warmweather, and populations can build upquickly in situations where naturalenemies are destroyed and weather isfavorable. Most whiteflies, especiallythe most common pest speciesgreen-house whitefly (Trialeurodesvaporariorum) and silverleaf orsweetpotato whiteflies (Bemisia spe-cies)have a wide host range thatincludes many weeds and crops. Inmany parts of California, they breed allyear, moving from one host to anotheras plants are harvested or dry up.

Whiteflies normally lay their tiny, ob-long eggs on the undersides of leaves.The eggs hatch, and the young white-flies gradually increase in size throughfour nymphal stages called instars (Fig.1). The first nymphal stage (crawler) is

barely visible even with a hand lens.The crawlers move around for severalhours, then settle and remain immo-

bile. Later nymphal stages are oval andflattened like small scale insects. Thelegs and antennae are greatly reduced,and older nymphs do not move. Thewinged adult emerges from the lastnymphal stage (for convenience some-times called a pupa). All stages feed bysucking plant juices from leaves andexcreting excess liquid as drops ofhoneydew as they feed.

Table 1 lists common whiteflies in Cali-fornia gardens and landscapes.

DAMAGEWhiteflies suck phloem sap. Largepopulations can cause leaves to turnyellow, appear dry, or fall off plants.Like aphids, whiteflies excrete honey-dew, so leaves may be sticky or cov-ered with black sooty mold. Thehoneydew attracts ants, which inter-fere with the activities of natural en-emies that may control whiteflies andother pests.

Feeding by the immature silverleafwhitefly, Bemisia argentifolii, can causeplant distortion, discoloration, or sil-vering of leaves and may cause serious

Figure 1. Greenhouse whitefly life cycle.

eggs

adult

fourthinstarnymph

third instar nymph

secondinstarnymph

crawler

(actualsize)


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September 2002 Whiteflies

Ash whitefly Host plants: many broadleaved trees and shrubs

(Siphoninus phillyreae) including ash, citrus, Bradford pear and other

flowering fruit trees, pomegranate, redbud, toyon

Characteristics : Fourth-instar nymphs have a very thick

band of wax down the back and a fringe of tiny tubes,

each with a liquid droplet at the end. Adults are white.

Bandedwinged whitefly Host plants: very broad including cotton, cucurbits,

(Trialeurodes abutilonea) other vegetables

Characteristics: Fourth-instar nymphs have short, waxy

filaments around their edges. Adults have brownish bands

across the wings, and their body is gray.

Citrus whitefly Host plants: citrus, gardenia, ash, ficus, pomegranate

(Dialeurodes citri) Characteristics: Fourth-instar nymphs have no fringe

around their edges but have a distinctive Y-shape on theirbacks. Adults are white.

Crown whitefly Host plants: oak, chestnut

(Aleuroplatus coronata) Characteristics: Fourth-instar nymphs are black with

large amounts of white wax arranged in a crownlike

pattern. Adults are white.

Giant whitefly Host plants: begonia, hibiscus, giant bird of paradise,

(Aleurodicus dugesi i) orchid tree, banana, mulberry, vegetables, and

many ornamentals; currently only in SouthernCalifornia

Characteristics: Adults are up to 0.19 inch long. They

leave spirals of wax on leaves. Nymphs have long

filaments of wax that can be up to 2 inches long and give

leaves a bearded appearance. For more information, see

Pest Notes: Giant Whitefly, listed in References.

Greenhouse whitefly Host plants: very broad including most vegetables and

(Trialeurodes vaporariorum) herbaceous ornamentals

Characteristics: Fourth-instar nymphs have very long

waxy filaments and a marginal fringe. Adults have white

wings and a yellow surface or substrate.

Iris whitefly Host plants: iris, gladiolus, many vegetables, cotton and

(Aleyrodes spiraeoides) other herbaceous plants

Characteristics: Fourth-instar nymphs have no fringe or

waxy filaments but are located near distinctive circles of

wax where egg laying took place. Adults have a dot on

each wing and are quite waxy.

Continued on next page

losses in some vegetable crops. Somewhiteflies transmit viruses to certainvegetable crops. With the notable ex-ception of the citrus whitefly, white-flies are not normally a problem infruit trees, but several whiteflies can be

problems on ornamental trees (seeTable 1). Low levels of whiteflies arenot usually damaging. Adults by them-selves will not cause significant dam-age unless they are transmitting a plantpathogen. Generally, plant losses donot occur unless there is a significantpopulation of whitefly nymphs.

MANAGEMENT

Management of heavy whitefly infesta-tions is very difficult. Whiteflies arenot well controlled with any availableinsecticides. The best strategy is to

prevent problems from developing inyour garden to the extent possible. Inmany situations, natural enemies willprovide adequate control of whiteflies;outbreaks may occur if natural enemiesthat provide biological control ofwhiteflies are disrupted by insecticideapplications, dusty conditions, or inter-ference by ants. Avoid or removeplants that repeatedly host high popu-lations of whiteflies. In gardens, white-fly populations in the early stages ofpopulation development can be helddown by a vigilant program of remov-ing infested leaves, vacuuming adults,or hosing down (syringing) with watersprays. Aluminum foil or reflectivemulches can repel whiteflies from veg-etable gardens and sticky traps can beused to monitor or, at high levels, re-duce whitefly numbers. If you chooseto use insecticides, insecticidal soaps oroils such as neem oil may reduce butnot eliminate populations.

Biological ControlWhiteflies have many natural enemies,and outbreaks frequently occur whenthese natural enemies have been dis-turbed or destroyed by pesticides, dust

buildup, or other factors. Generalpredators include lacewings, bigeyed

bugs, and minute pirate bugs. Severalsmall lady beetles includingClitostethus arcuatus (on ash whitefly)and scale predators such as Scymnus orChilocorus species, and the Asian multi-

Table 1. Major Economic Hosts of Some Common Whiteflies.


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Mulberry whitefly Host plants: citrus, other trees

(Tetraleurodes mori) Characteristics: Nymphs have blackish, oval bodies

with white, waxy fringe.

Silverleaf and sweetpotato Host plants: very broad including many herbaceous and

whiteflies (Bemisia some woody plants such as cotton, cucurbits, tomatoes,

argentifoliiand B. tabaci) peppers, lantana, cole crops, and hibiscus

Characteristics: Fourth-instar nymphs have no waxy

filaments or marginal fringe. Adults have white wings and

yellow body; they hold their wings slightly tilted to surface

or substrate.

Woolly whitefly Host plants: citrus, eugenia

(Aleurothrixus floccosus) Characteristics: Nymphs are covered with fluffy, waxy

filaments.

Table 1, continued. Major Economic Hosts of Some Common Whiteflies.

colored lady beetle, Harmonia axyridis,feed on whiteflies. Whiteflies have anumber of naturally occurring para-sites that can be very important in con-trolling some species. Encarsia spp.parasites are commercially availablefor release in greenhouse situations;however, they are not generally recom-mended for outdoor use because theyare not well adapted for survival intemperate zones. An exception is theuse of parasite releases for bayberrywhitefly in citrus in southern Califor-nia. You can evaluate the degree of

natural parasitization in your plants bychecking empty whitefly pupal cases.Those that were parasitized will haveround or oval exit holes and those fromwhich a healthy adult whiteflyemerged will have a T-shaped exit hole(Fig. 2). Whitefly nymphs can some-times be checked for parasitization

before emergence by noting a darken-ing in their color. However, some

whitefly parasites do not turn hostsblack and many whitefly nymphs thatoccur on ornamentals are black in theirunparasitized state.

Avoiding the use of insecticides thatkill natural enemies is a very importantaspect of whitefly management. Prod-ucts containing carbaryl, pyrethroids,diazinon or foliar sprays of imidaclo-prid can be particularly disruptive.Control of dust and ants, which protectwhiteflies from their natural enemies,can also be important, especially in

citrus or other trees.

RemovalHand-removal of leaves heavily in-fested with the nonmobile nymphaland pupal stages may reduce popula-tions to levels that natural enemies cancontain. Water sprays (syringing) mayalso be useful in dislodging adults.

A small, hand-held, battery-operatedvacuum cleaner has also been recom-mended for vacuuming adults offleaves. Vacuum in the early morning

or other times when it is cool andwhiteflies are sluggish. Kill vacuumedinsects by placing the vacuum bag in aplastic bag and freezing it overnight.Contents may be disposed of the nextday.

MulchesAluminum foil or reflective plasticmulches can repel whiteflies, especially

away from small plants. Aluminum-coated construction paper is availablein rolls from Reynolds AluminumCompany. Alternatively, you can sprayclear plastic mulch with silver paint.

Reflective plastic mulches are alsoavailable in many garden stores.

To put a mulch in your garden, firstremove all weeds. Place the mulch onthe plant beds and bury the edges withsoil to hold them down. After themulch is in place, cut 3- to 4-inch diam-eter holes and plant several seeds orsingle transplants in each one. Youmay furrow irrigate or sprinkle your

beds if you use aluminum-coated con-struction paper or other porous mulch;the mulch is sturdy enough to tolerate

sprinkling. Plastic mulches will requiredrip irrigation. In addition to repellingwhiteflies, aphids, and leafhoppers, themulch will enhance crop growth andcontrol weeds. Mulches have beenshown to deter the transmission ofviruses in commercial vegetable crops.When summertime temperatures gethigh, however, remove mulches toprevent overheating plants.

TrapsIn vegetable gardens, yellow stickytraps can be posted around the garden

to trap adults. Such traps wont elimi-nate damaging populations but mayreduce them somewhat as a compo-nent of an integrated managementprogram relying on multiple tactics.Whiteflies do not fly very far, so manytraps may be needed. You may need asmany as one trap for every two largeplants, with the sticky yellow part ofthe trap level with the whitefly infesta-tion. Place traps so the sticky side facesplants but is out of direct sunlight.

Commercial traps are commonly avail-

able, or you can make traps out of14-inch plywood or masonite board,painted bright yellow and mounted onpointed wooden stakes that can bedriven into the soil close to the plantsthat are to be protected. Although com-mercially available sticky substratessuch as Stickem or Tanglefoot are com-monly used as coatings for the traps,you might want to try to make your

Figure 2. Look at empty nymphal casesto detect parasitism: a healthy adultwhitefly emerged from the T-shapedhole in the mature nymph on the left,whereas an adult parasite emerged fromthe round hole on the right.


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For more information contact the University

of California Cooperative Extension or agri-

cultural commissioners office in your county.

See your phone book for addresses and

phone numbers.

AUTHOR: M. L. Flint

EDITOR: B. Ohlendorf

DESIGN AND PRODUCTION: M. BrushILLUSTRATIONS: from M. L. Flint. July

1995. Whiteflies in California: a Resource for

Cooperative Extension. UC IPM Publ. 19.

Giant whitefly in Table 2 by D. H. Hendrick.

Produced by IPM Education and Publica-

tions, UC Statewide IPM Program, University

of California, Davis, CA 95616-8620

This Pest Note is available on the World

Wide Web (http://www.ipm.ucdavis.edu)

This publication has been anonymously peer re-viewed for technical accuracy by University of Cali-fornia scientists and other qualified professionals.This review process was managed by the ANR As-

sociate Editor for Pest Management.

To simplify information, trade names of productshave been used. No endorsement of named productsis intended, nor is criticism implied of similar productsthat are not mentioned.

This material is partially based upon work supportedby the Extension Service, U.S. Department ofAgriculture, under special project Section 3(d),Integrated Pest Management.

WARNING ON THE USE OF CHEMICALSPesticides are poisonous. Always read and carefully follow all precautions and safety recommendations

given on the container label. Store all chemicals in the origina l labeled containers in a locked cabinet or shed,away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock.

Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especiallygardens containing fruits or vegetables ready to be picked.

Do not place containers containing pesticide in the trash nor pour pesticides down sink or toilet. Eitheruse the pesticide according to the label or take unwanted pesticides to a Household Hazardous WasteCollection site. Contact your county agricultural commissioner for additional information on safe container

disposal and for the location of the Household Hazardous Waste Collection site nearest you. Dispose ofempty containers by following label directions. Never reuse or burn the containers or dispose of them in sucha manner that they may contaminate water supplies or natural waterways.

The University of California prohibits discrimination against or harassment of any person employed by orseeking employment with the University on the basis of race, color, national origin, religion, sex, physicalor mental disability, medical condition (cancer-related or genetic characteristics), ancestry, marital status,age, sexual orientation, citizenship, or status as a covered veteran (special disabled veteran, Vietnam-eraveteran, or any other veteran who served on active duty during a war or in a campaign or expedition for whicha campaign badge has been authorized). University policy is intended to be consistent with the provisionsof applicable State and Federal laws. Inquiries regarding the Universitys nondiscrimination policies may bedirected to the Affirmative Action/Staff Personnel Services Director, University of California, Agriculture andNatural Resources, 300 Lakeside Dr., Oakland, CA 94612-3350; (510) 987-0096.

own adhesive from one-part petroleumjelly or mineral oil and one-parthousehold detergent. This material can

be cleaned off boards easily with soapand water, whereas a commercial sol-vent must be used to remove the other

adhesives. Periodic cleaning is essen-tial to remove insects and debris fromthe boards and maintain the stickysurface.

Insecticide SpraysInsecticides have only a limited effecton whiteflies. Most kill only thosewhiteflies that come in direct contactwith them. For particularly trouble-some situations, try insecticidal soap or

an insecticidal oil such as neem oil ornarrow-range oil. Because these prod-ucts only kill whitefly nymphs that aredirectly sprayed, plants must be thor-oughly covered with the spray solu-tion. Be sure to cover undersides of all

infested leaves; usually these are thelowest leaves and the most difficult toreach. Use soaps when plants are notdrought-stressed and when tempera-tures are under 80F to prevent pos-sible damage to plants. Avoid usingother pesticides to control whiteflies;not only do most of them kill naturalenemies, whiteflies quickly build upresistance to them, and most are notvery effective in garden situations.

REFERENCESBellows, T. S., J. N. Kabashima, andK. Robb. Jan. 2002. Pest Notes: GiantWhitefly. Oakland: Univ. Calif. Agric.Nat. Res. Publ. 7400. Also availableonline at http://www.ipm.ucdavis.

edu/PMG/PESTNOTES/pn7400.html

Flint, M. L. 1998. Pests of the Garden andSmall Farm. 2nd ed. Oakland: Univ.Calif. Agric. Nat. Res. Publ. 3332.

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