White Flies Paper 2

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Crop & Food Research, Broadsheet No. 91, February 1999

Fourteen species of whitefly are known in New Zealand.

Eight of them are indigenous (native) and six are introduced

species. The latter include several pests that are resistant to

many pesticides and that growers find dif ficult to control. For

effective and sustainable pest control i t is important to know

which species of whitefly are present and to understand the

insects biology and the full range of control options. Four

broadsheets have been prepared on these topics. This

broadsheet provides information on the identif ication, biology

and life cycle of the pest. The second broadsheet (No. 92)

provides information on the natural enemies of whitefly while

the third broadsheet (No. 93) describes the principles of

whitefly control, the range of methods available and how to

prevent and manage resistance to pesticides. The fourth

broadsheet (No. 94) provides advice about how to reduce the

chance of whitefly infesting your crops and guidance about

how to control the pests. Broadsheet No. 94 will be updated

regularly. You can obtain copies of these broadsheets from

the Publications Coordinator, Crop & Food Research, Private

Bag 4704, Christchurch, for a small charge.

What are whitefly and what do they looklike?

Whitefly are small insects with sucking mouth parts.They belong to the fami ly Aleyrodidae (Suborder

Homoptera) and are related to other families of sucking

insects including aphids, plant hoppers, scale insects and

mealy bug s. Adu lt whitefly are about 1.5 mm long. In New

Zealand they are yellow to white and are covered with a

pow dery w ax which is usually bright white (Figs 1 and 2)

although the cabbage wh itefly has da rk flecks on its wings

(Fig. 3). Adu lts have tw o pairs of wings th at are held over

the bod y w hen at rest. While single wh itefly can be d ifficult

to see, large num bers clustered on the un dersid e of leaves

are very obvious. They tend to f ly when the plant is

disturbed. The male whitefly is similar to the female but

slightly sma ller.

Fig. 1: Greenhouse whitefly adults. Note the pure white wings and

triangular shape when viewed from the top.

Fig. 2: Sweet potato whitefly adult. N ote the pure white wings and that

the wings are held parallel to the body. Compare this w ith the greenhouse

whitefly in Fig. 1.

Editor: NA Martin

Biology, identification and life cycle

New Zealand Institute for Crop & Food Research LimitedA Crown Research Institute

A wh ite flying insect often seen in spring an d confused

with p est whitefly is the moth fly (family Psychod idae). This

is a true fly (Diptera) with only tw o wings. It is about twice

the size of wh itefly with greyish scale-covered w ings with a

dar k fleck (Fig. 4). The larvae feed on dead and decaying

plants.

Whitefly lay eggs on the leaf surface, either on end

(Fig. 5) or on their side (Fig. 6). The first stage nymph is


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scale-like but h as legs and may craw l a short d istance from

the egg before feeding and settling, usu ally on the leaf upon

wh ich th e egg wa s laid. The first stage nymp h is also called

a crawler. It moults into a legless scale-like creature, the

second stage nymph. There are four scale-like nymphal

stages (Figs 7 and 20) wh ich stay on the leaf upon which the

crawler settles. The last nymph al stage swells up and wh en

fully grown the whitefly pupates inside the nymphal skin

which is now termed a puparium (Figs 8 and 9). Shortly

before the adult emerges its eyes can be seen through the

pu par ial skin. The skin splits to allow th e adu lt whitefly to

emerge and expand its wings, which are clear at first but

soon become covered with wh ite wax (Fig. 16).

What plants do they live on?

The host plants of the whitefly in New Zealand are

shown in Tables 1 and 2. Some strains (races) of certain

whitefly species prefer p articular h ost plants. Host p lant

strains are known in two sp ecies of whitefly that hav e a

very wid e host range. Sweet pota to wh itefly (Bemisia tabaci)

has a nu mber of strains which differ in host plant r ange,

ability to produ ce plant disorders and ability to transmit

viruses. One strain (Strain B or Poinsettia strain), which

causes silver leaf symptoms in pumpkin and squash, is

considered to be a separate species (B. argentifolii) in the

USA. In New Zealand both Strain A and Strain B have been

found and were primarily associated with p oinsett ia,

hibiscus and begon ias. Strain B has th e poten tial to infestbrassicas, tomatoes and cucumbers and is a severe pest in

the Cook Islands.

Greenhouse whitefly (Trialeurodes vaporariorum) is a

major pest of tomatoes, cucumbers and several other

economic plants especial ly when they are grown in

greenh ouses. It also has a strain that atta cks tamarillo. The

species can be found on a wide selection of weeds,

including sow thistles (Sonchus spp .), milkweed (Euphorbia

peplus), and mallows (Malva spp .) (See Broad sheet N o. 93

for photograp hs.) However, the su ites of weeds attacked

vary with d istrict and prop erty suggesting that there arelocal host p lant strains.

Which whitefly is which?

Whitefly in the bush

Little is known about N ew Zealand s eight indigenous

species. They ap pear to be restricted to native plants in their

natural environment. One species, Trialeurodes asplenii, is

found in the bush on native ferns while the other species

hav e been foun d on trees (Table 1).

Fig. 3: Cabbage whitefly adult. Note the black patches on the wings.

Fig. 4: Moth fly adult. This harmless fly is sometimes mistaken for

whitefly. It is twice as large and has fuzzy grey-white wings with dark

markings.

Fig. 5: Greenhouse whitefly eggs inserted into a plant leaf. They are

cream coloured when first laid then turn black.


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Table 1: Native whitefly and their host plants.

Whitefly Host plant

Aleyrodes fodiens(Maskell) Pseudowintera axillaris

Aleyrodes winteraeTakahashi Pseudowintera colorata,Pepper tree

Asterochiton aureusMaskell Melicytus ramiflorus,

whiteywood

Asterochiton cerata(Maskell) Nothofagus menziesii,silver beech

Asterochiton fagi(Maskell) Nothofagus menziesii,silver beech

Asterochiton pittosporiDumbleton Pittosporum eugenoides,lemonwood

Asterochiton simplex(Maskell) Pittosporum eugenoides,Coprosma lucidaandseveral other trees

Trialeurodes asplenii (Maskell) Aspleniumspecies, ferns

Whitefly on crops, in the garden, in greenhousesand on introduced plants

The various species of whitefly are difficult to identify

even for an expert. However, there are several visual clues

that create a reasonable chance of correct identification.

Features to look for are wing colour, wing shape and the

puparia. Identify the host plant and if the whitefly appear

on an un usu al plant (see Table 2 for a list of usual host p lants)

have sp ecimens id entified by an expert. Send leaves with

pu paria to MAF Diagnostic Laboratories (see last p age for

addresses).

Table 2: Introduced whitefly and their host plants.

Common name Scientific name Host plants

Aleuroclava eucalypti EucalyptusSingh

Ash whitefly Siphonius phillyreae Ash, and many deciduous trees(Halliday) (in summer) and e.g. cit rus and

hawthorne (in winter)

Azalea whitefly Pealius azaleae Rhododendron and azalea(Baker & Moles) species

Cabbage whitefly Aleyrodes proletella Brassicas and sowLinnaeus thistle species

Greenhouse Trialeurodes Very varied,including tamarillowhitefly vaporariorum and several vegetables

Sweet potato Bemisia tabaci Very varied, including poinsettiawhitefly or silver (Gennadius) hibiscus, begonia and gerberaleaf whitefly B. argentifolii

Bellows et al.

The most common wh itefly is the greenhou se whitefly,

Trialeurodes vaporariorum, which is found on many outdoor

plants an d greenh ouse crops. The wings are entirely white

(Fig. 1) and it is mainly found on herba ceous plants bu t also

on tam arillo.

A recent arrival, currently restricted to orn amental plants

grown in greenhou ses, is the sweet potato w hitefly,Bemisiatabaci, also know n as silver leaf wh itefly,B. argentifolii. The

Fig. 6: Cabbage whitefly eggs are laid on their sides and often in circles

around where the female was feeding.

Fig. 7:Greenhouse whitefly nymphs. Note the flat, oval shape.

Bemisia species foun d in New Zealand can be distinguished

from greenhouse w hitefly by the p arallel sides of the wings

when viewed from above (Fig. 2) and by details of the

pu pariu m (Fig. 12).

If the adult has a black fleck on the wing (Fig. 3), it is

probably the cabbage whitefly, A leyrodes proletella. It isusu ally foun d on b rassicas and sow thistles (Sonchus spp.),

also called m ilky thistles.

Three species are restricted to trees and shrubs, A .

eucalypti on Eucalyptus, the azalea wh itefly on azaleas and

rhododend rons, and th e ash w hitefly on m any d ifferent trees

and shrubs. The pup aria of the ash and azalea whitefly are

distin ctive (Figs 14 and 15).


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Fig. 9: Greenhouse whit efly puparium . The scann ing electron micrograph

shows the long wax rods and side walls fringed with short wax rods.

Fig. 10: Excretory organ of greenhouse whitefly puparium. The orifice

has an organ (ligular) that flicks away the honeydew. The knobbly shape

of the ligular distinguishes greenhouse whitefly from sweet potato

whitefly.

Fig. 11: Sweet potato whitefly pu parium, scanning electron micrograph.

Note the absence of side walls with a fringe of short wax rods. The wax

rods are longer when the whitefly nymph is on a hairy plant compared

to a smooth-leaved plant.

Fig. 12: Excretory organ of sweet potato whitefly puparium. Note the

smooth shape to the ligular compared to the knobbly structure in

greenhouse whitefly (Fig. 10).

Fig. 13: Cabbage whitefly puparium, scanning electron micrograph. Note

the lack of long wax rods.

Fig. 8: Mature fourth stage greenhouse whitefly ny mphs. The body has

swollen up and has long and short wax hairs.


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How do they live and damage plants?

Adu lt whitefly are mainly foun d on th e young leaves of

plants where they feed and lay eggs. The nymphs stay on

the leaf on wh ich they were laid as eggs. This results in older

nymp hs being found on older leaves. Depending on h ow

fast the shoot is growing the oldest nym ph s may be close tothe shoot tip or man y (e.g. more th an 16) leaves awa y. Both

adults and nymphs tend to be found on the underside of

plant leaves. Whitefly can dam age plants in four waysby

direct damage w hen feeding, by indirect damage following

the secretion of sugars (honey dew), by physiological

disorders and by transmitting plant-dam aging viruses.

Feeding damage

Adults and n ymphs have long sucking mouth parts that

penetrate the ph loem (nutrient-condu cting vessels) of leaves

and withd raw th e sap. If a lot of wh itefly feed off one plantthey can cause deformation, defoliation and plant death.

When fewer whitefly are present plants may w ilt and require

more frequent w atering because of the loss of sap.

Honey dew and sooty mould

Much of the water and sugar in the p lant sap is excreted

as honey d ew, wh ich falls onto p lant leaves and fruit below

wh ere wh itefly are feeding. Large nu mbers of wh itefly on

trees can m ake pav ements an d cars sticky. The sticky honey

dew makes plants and fruit unpleasant to handle. In humid

conditions, the black sooty mould fungus grows on thehoney dew and blackens leaves and fruit (Fig. 17). It can

make plants unsaleable and means that fruit must be washed

before packing. Dense sooty m ould on leaves can also block

out sunlight and inh ibit ph otosynthesis.

Physiological disorders

A characteristic of the silver leaf whitefly is that small

numbers cause distinct disorders on certain plants, for

example the silver leaf symptoms on squash and pu mpkins

(Fig. 18), and un even rip ening of tom atoes.

Virus transmission

Two sp ecies of whitefly in N ew Zealand are know n to

transmit viruses. Greenhouse w hitefly can tran smit a few

viruses of wh ich only beet pseud o yellow virus m ay be in

New Zealand. Bemisia tabaci t ransmits many viruses,

especially gemini viruses. These can cau se severe dam age

to many plants of economic importance. The only gemini

virus known in New Zealand, abutilon mosaic gemini virus,

causes bright yellow variegation in Abutilon species (Fig.

19). Growers d eliberately prop agate viru s-infected shrubs

because they are regarded as attractive.

Fig. 14:Ash whitefly pu paria. N ote the fringe of waxy knobs and central

mass of white wax.

Fig. 15: Azalea nymphs and puparia. Note the yellow body and white

wax fringe.

Fig. 16:Adult greenhouse whitefly just emerged from puparia. Note the

split skin in the puparia and the clear wings of the adults prior to the

deposition of white wax.


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Fig. 18: Silver leaf on squash in the Cook Islands. The silvering of

leaves is a physiological response by the plant to feeding by Bemisia

tabaci Strain B or silver leaf whitefly.

Fig. 19:Yellow variegated leaves of abutilon. The variegation is caused

by a gemini virus.

Fig. 17: Black sooty mould growing on greenhouse tomatoes. Note

the absence of white skins which is characteristic of sooty mould caused

by aphids.

Life cycle

Greenhouse w hitefly, cabbage whitefly and some other

species breed all year, especially in warmer parts of the

country and in greenhou ses. In these situations all life stages

may be found all year round . All whitefly hav e a similar life

cycle (Fig. 20). The adult females tend to feed on you nger,more nutritious leaves. Eggs are laid on end with the tip

inserted into th e leaf or on their sid es (Figs 5 and 6). The

num ber of eggs laid per d ay varies with temperature and

suitability of host plan t, but a female can lay more than eight

per day and between 150 and 300 in a lifetime. Like all

insects, whitefly grow by mou lting or sh edd ing their skin

between each instar or stage.

Crawlers (first instar nym ph s) hatch out of eggs. They

have three pairs of functional legs and an tennae and wand er

over the leaf until they su ccessfully p robe the leaf to obtain

sap from the phloem. Once a good feeding site has beenfound wh itefly remain immobile until they become ad ults.

Second and third instar (stage) nym phs are flat, oval-shaped

and scale-like (Fig. 7). The fourth instar starts off flat and

oval like the third instar, but it swells and becomes denser

and develops th e characteristic app earance of the species.

This can includ e waxy and sp ine-like processes (see Figs 9-

15). The fully grown nymph stops feeding and pupates

within the n ymp hal skin. It is now called a puparium. The

adult develops in the puparium. Before hatching the eyes

and outline of the body can be seen through the skin.

Adult whitefly force open a T-shaped split in thepuparium (Fig. 16) and emerge. The wings are expanded

and grow a covering of wax. After a few hour s they can fly

and m ay mate du ring the next few d ays. Depending up on

temperature, egg laying may start in one to three days.

During th e first few days th ey move from the old leaves on

wh ich they have hatched to you nger leaves on the same or

a different plant. Eggs from u nma ted females produ ce only

males whereas eggs from mated females may produce

females and males. The time of development from egg to

adu lt of each species depends u pon temp erature and on host

plant. Development is faster at higher tempera tures and onmore favou rable host s (Tables 3 and 4).

Greenhouse whitefly. Trialeurodes vaporariorumis the

commonest species in New Zealand. It may be found all

year round in greenhou se crops and ou tdoors in the warmer

parts of the coun try. On plants w ith smooth leaves, eggs are

laid in circles around the point of feeding, but on h airy leaves

eggs are laid rand omly.

After hatching, female greenhouse whitefly take 2 days

at 22C before they can lay eggs (pre-ovipositional period )

and on tomatoes at this temperature they can lay 6 eggs per

day. At 22C on tom atoes the tim e requ ired for each juvenilestage is: egg, 7 days; nymph 1, 4 days; nym ph 2, 4 days; nymp h


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3, 4 days; nymph 4 and pupa, 9 days. Development ceases

below 8C and above 35C and egg laying stops below 7C.

Amongst greenh ouse crops, the most favourable host is

eggplant and the least favoured is capsicum. Host plants

from good to poor are: eggplant > cucumber > gerbera >

tomato > capsicum .

Table 3: Development of greenhouse whitefly ontomatoes. Duration (in days) of each stage and eggs laid perfemale on tomato.

Temperature C

Life stage 12 16 20 24 28

Average adult lifespan 30 41 41 30 12

Egg to adult 64 48 33 25 18

Egg 17 13 8 6.5 5

Eggs laid per female 60 140 160 130 70

Table 4: Development of greenhouse whitefly on fourvegetables at 22C .

Note: the differences in data on tomatoes in Tables 3 and 4reflect different experimental procedures. However, thecomparisons within tables are valid.

Life stages Eggplant Cucumber Tomato Capsicum

Adult female28 21.1 20.4 4.8

longevity (days)

Number of eggs286 175 94 3

per female

Number of eggs10.1 8.3 4.7 0.7

per female per day

Egg to adult (days) 25 26 28 30

Mortality (%)9 11 21 92

of juveniles

Sweet potato whitefly/silver leaf whitefly. Thereapp ear to be many strains ofBemisia tabaci around th e world

which vary in host plant range and ability to transmit

viruses. One strain,B. tabaci Strain B, or poinsettia strain,

has also been named as a separate species, B. argentifolii.

This strain has recently spread throughout the world and

may be th e strain in New Zealand. Strain B is resistant to

many pesticides, has a very wide host range and causes

ph ysiological disorders in some p lants such as silver leaf in

squash. Sweet potato whitefly has been in New Zealand

since at least 1990 but th e strain present m atches no know n

overseas strain. At present the species is restricted to

greenhouses in New Zealand and is mainly found on

poinsettias and other ornam ental plants includ ing begonia

and hibiscus. However, the insect has a very w ide host range

includ ing most g reenhou se vegetable crops. The strain(s)

in New Zealand are not known to live on kum ara.

Fig. 20: Life cycle of greenhouse whitefly.

In New Zealand one strain of greenhouse whitefly is

ada pted to tamarillo. Females of both the norma l strain and

tamarillo strain feed and lay eggs on tamarillo, but most

juveniles of the normal whitefly die when developing on

this host whereas most tamarillo juveniles survive. The

tamarillo strain was first noticed d uring the late 1970s and

is now a major insect pest of the crop.

Other strains of greenhouse w hitefly may be adap ted to

different weed s; for example, on m ost prop erties whitefly are

not found on docks,Rumex spp ., whereas in some p laces large

numbers of whitefly can be found breeding on docks. This

mean s the host p lants of whitefly must be checked locally.

Table 5: The development of sweet potato/silver leafwhitefly on poinsettia (duration in days of life stage andeggs laid per female).

Temperature CLife stage 16 22 28

Average adult lifespan 50 22 16

Egg to adult 137 39 23

Egg 34 13 8

Eggs laid per female 60 91 96

On p oinsettias the pre-ovipositional period is 3 day s at

22C. It is shorter at higher temperatures. The number of

eggs laid p er day increases to 4.5 for the first 8-20 da ys and

then declines, while at 28C it peaks at 7 per day. The

minimum temperature for insect development is about 14C

whi le the upper l imi t i s above 35C. The opt imal

developm ental temp erature is abou t 25-28C.


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Ash whitefly was discovered in New Zealand in

Auckland in May 1995. It is spread ing bu t at th e end of 1997

it was still only found in the greater Auckland region an d

Ham ilton. In summ er it primarily lives on decidu ous trees

with a p reference for ash trees, althou gh species in 16 families

may be hosts. In the winter it persists on hawthorne and

can breed on evergreen trees such as citrus. Females tend to

lay eggs on m ature leaves. They are laid on their side and

usu ally in a circular p atch about 1-2 cm d iameter wh ich is

dusted with a white bloom of wax from the female. Ash

whi tef ly completes severa l genera t ions a year and

pop ulations can mu ltiply rapid ly.

Identification of whitefly

Microscopic examination is requ ired to iden tify whitefly

with certainty. This can be undertaken by commercial

laboratories suh as

Agri-Quality NZ Ltd

Box 41, Auckland 1015

Tel. 09 626 6026

Contact the MAF laboratories below for d etails of other

laboratories offering a d iagnostic service. Correct identification

will enable app ropriate control strategies to be used.

New w hitefly (and other pests) have been found in New

Zealand in recent years. If you find a wh itefly (or other insect)

on a plant tha t is not norm ally a host, collect adults and pu pariainto a sealed container. Identification of suspected n ew pests is

free. Take or send specimens in a non-crushable container to:

MAF (National Plant Reference Laboratory)

Box 2095, Au ckland 1015

Tel. 09 627 2534

or

MAF (National Plant Reference Laboratory)

Box 24, Lincoln, Canterbury

Tel. 03 325 3900

AcknowledgementsPaul Sutherland (HortResearch) for scanning electron

micrograph s; John Charles (Hor tResearch), Terril Marais

(Vegfed) and Rosa Hen der son (Landcare) are acknow ledged

for their assistance du ring the prep aration of this broadsh eet.

N A Martin

Crop & Food ResearchMount Albert Research CentrePrivate Bag 92 169Auckland

120 Mount Albert RoadMount AlbertAuckland

Tel. 64 9 815 4200Fax 64 9 815 4201

Email:[email protected]

Crop & Food Research(Head Office)

Private Bag 4704ChristchurchNew Zealand

Tel. 64 3 325 6400Fax 64 3 325 2074

http://www.crop.cri.nz

Contacts

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