Encarsia formosa
Whitefly parasitoid- Rate
- 1–10 /m² per release, weekly until control is achieved
- Temp
- 20–25 °C best (UMass: 21–26 °C); weak below a 17 °C daily average
- Best for
- Greenhouse and conservatory; long crops, from the first whitefly
Pest
Greenhouse whitefly
Trialeurodes vaporariorum
The short answer
This is the whitefly most people mean by "whiteflies": a sap-feeding bug about 1/16 in (1.5 mm) long with white wings held flat over its back. It breeds all year in greenhouses and on houseplants, and moves into vegetable gardens in warm weather. The nymphs under the leaves do most of the feeding. Leaves turn sticky, then black with sooty mould, and yellow under heavy attack. Low numbers do little harm. In a greenhouse, the parasitic wasp Encarsia formosa is the standard control. In gardens and homes, hosing, pruning infested leaves and soap or oil sprays keep it down; broad-spectrum sprays tend to make whiteflies worse.
hero macro · adults and scale-like nymphs on a leaf underside
Adult Trialeurodes vaporariorum and nymphs on a tomato leaf underside. Photo: pending.
Identification
Adults are about 1/16 in (1.5 mm) long, with a yellowish body and four whitish wings held flat over the back, so that the wings meet along the midline with no gap. They sit on leaf undersides and fly up in a cloud when the plant is disturbed. Despite the name they are not flies but true bugs, related to aphids and scale insects.
The young stages live on the undersides of the lower leaves. The first stage, the crawler, moves around for several hours and then settles. Later nymphs are flat, pale, oval and immobile, like tiny scale insects, and just over 1 mm long when full-grown. The last stage, often called the pupa, is the one to check. In greenhouse whitefly its sides rise straight up from the leaf and are fringed with long wax filaments. Silverleaf (tobacco) whitefly, the other common species, has few or no long filaments and sides that slope down to the leaf, and its adults hold their wings tilted like a roof.
Black scales are nymphs that have been parasitised, usually by Encarsia, and are dead. Empty white cases with a T-shaped slit are where adult whiteflies came out; a round hole means a parasitoid emerged.
Easily confused with
- Silverleaf whiteflyAlso a pestGreenhouse whitefly holds its wings flat, meeting over the back; silverleaf whitefly tilts them roof-like with a gap. Greenhouse whitefly pupae have upright edges and long wax filaments.
- Parasitised whitefly scalesBeneficial — leave itBlack scales among the pale ones are parasitised by Encarsia. Leave them: the wasp emerges through a small round hole.
- Bandedwinged whiteflyAlso a pestBandedwinged whitefly has brownish bands across its wings, and its nymphs have only short wax filaments.
Damage symptoms
All stages suck sap, and the nymphs do most of the damage. UC IPM's view is that low numbers are not usually damaging: adults alone do little unless they carry a virus, and plants are lost only under a sizeable population of nymphs. The honeydew is the usual complaint. It makes leaves and fruit sticky and feeds a black sooty mould that shades the leaf. Greenhouse whitefly also transmits tomato infectious chlorosis virus, which UC IPM says can cause heavy losses in fresh-market and greenhouse tomatoes.
- Clouds of small white adults that fly up when the plant is touched, then resettle
- Sticky, shiny honeydew on leaves, fruit and whatever sits beneath the plant
- Black sooty mould growing on the honeydew
- Yellowing, dry-looking or dropping leaves under heavy infestation
- Flat, pale, oval scales under the lower leaves — black ones are parasitised
Lifecycle & degree days
Greenhouse whitefly breeds continuously wherever it is warm, so all stages are present at once. How long a generation takes depends on temperature. RHS gives about three weeks at 70 °F (21 °C) and several months at 50 °F (10 °C). UMass gives 14–40 days from egg to adult for the two greenhouse species, depending on temperature, host and species. It does not survive winter outdoors in Massachusetts (UMass) and does not usually survive it in the UK (RHS). Garden infestations there start from greenhouse and bought-in plants, or from adults leaving greenhouses as the weather warms. In the warmer parts of California it breeds outdoors all year.
- Egg hatch
- About 4 days at 65–75 °F (18–24 °C)
- Egg to adult
- ~3 weeks at 70 °F (21 °C); months at 50 °F (10 °C)
- Eggs per female
- Up to 200 (UMass); over 200 (RHS)
- Adult lifespan
- Females up to 6 weeks
- Overwinters
- Indoors and in greenhouses; not outdoors in cold regions
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Host crops
A very broad host range: UC IPM lists most vegetables and herbaceous ornamentals, and RHS names cucumber, melon, tomato, pepper, chrysanthemum, gerbera, pelargonium, fuchsia, lantana, poinsettia and verbena. UMass calls whiteflies the major pest of poinsettias and greenhouse tomatoes. Not every whitefly is this one. RHS notes that the whiteflies on brassicas, Viburnum tinus, honeysuckle, azalea and rhododendron outdoors are other, host-specific species. In southern California and the southern San Joaquin Valley, silverleaf whitefly infests tomatoes too, and UC IPM finds greenhouse whitefly in all but the low desert.
Monitoring & action thresholds
Action threshold
None set
UC IPM states that no treatment threshold has been established for greenhouse whitefly on tomato. In gardens and homes, UC's advice is that low numbers are not usually damaging and that losses need a large population of nymphs, so the practical trigger is honeydew or sooty mould building up. In greenhouses the decision rests on weekly sticky-card counts, and Encarsia goes in at planting or when the first whiteflies are found, rather than at a set number (UMass).
Turn the leaves over: eggs are laid under the new growth, and the older scales sit under the lower leaves. In a greenhouse, UMass advises yellow sticky cards at about 1 per 1,000 sq ft, just above the crop, counted and replaced weekly, with extra cards near doors and vents and over susceptible crops. Take the cards down before releasing parasitoids and put them back 3–4 days later. Indoors, check new plants before they join the others. UC IPM and RHS both say whiteflies usually arrive on new plants.
Beneficial
Biological control
In a greenhouse or conservatory, the parasitic wasp Encarsia formosa is the established control. It lays eggs in the older nymphs, which turn black, so progress is easy to follow. UMass finds it most effective on crops grown for more than four months, at 70–80 °F (21–26 °C). Adults do not fly below 65 °F (18 °C), and it has to go in before plants are heavily infested (RHS). Eretmocerus eremicus suits hotter houses and attacks both whitefly species. The Swirski mite eats eggs and young nymphs, except on tomato. Delphastus is a costly clean-up beetle for dense patches. Outdoors, UC IPM does not generally recommend releasing Encarsia. Big-eyed bugs, lacewings, minute pirate bugs and small lady beetles already feed on whiteflies there, and outbreaks tend to follow when sprays, dust or ants disrupt them.
Eretmocerus eremicus
Whitefly parasitoid (Eretmocerus)- Rate
- 1–10 /m² per release, weekly
- Temp
- 77–84 °F (25–29 °C) best; needs a 68 °F (20 °C) daily average
- Best for
- Hot houses, or both whitefly species together
Amblyseius swirskii
Swirski mite- Rate
- 25–100 /m² per release; 100–300 /m² on hot spots
- Temp
- 20–32 °C best; not effective below 18 °C (Biobest: 15 °C)
- Best for
- Eggs and young nymphs; not on tomato
Delphastus catalinae
Whitefly ladybird- Rate
- 10 per infested plant or 100 per hot spot, weekly for 3–4 weeks
- Temp
- 72–80 °F (22–27 °C) best; suppliers quote working ranges as wide as 61–95 °F (16–35 °C); does not fly below 55 °F (13 °C)
- Best for
- Dense hot spots, alongside the wasps
Geocoris spp.
Big-eyed bugs- Kind
- Wild — attract it
- Best for
- Wild predator in gardens; protect it
Dicyphus hesperus
Dicyphus predatory bug- Rate
- 500 per acre (Arbico); trials used 1–3 adults per plant weekly for 3 weeks
- Temp
- Around 75 °F (24 °C), RH up to 50 % (Arbico); adults reared at 95 °F (35 °C) were smaller
- Best for
- Released early with mullein banker plants; slow to build
Beauveria bassiana strain GHA
Beauveria bassiana- Rate
- Label rate — BotaniGard ES / Mycotrol ES ½–2 qt per 100 gal (about 1–4 tsp per gallon); whiteflies and aphids ½–1 qt, thrips 1–2 qt
- Best for
- Fungal spray while numbers are low; cover leaf undersides
Cultural controls
Prevention and early physical control do more than sprays. UC IPM warns that even the most toxic insecticides are only partly effective against whiteflies.
- Inspect new plants, leaf undersides included, before they go into the greenhouse or join other houseplants; quarantine them if you can
- Prune out the first infested leaves while the infestation is still patchy
- Hose adults off with a strong stream of water; this also reduces the dusty conditions that favour whiteflies
- Hang yellow sticky traps to monitor adults; UC IPM says they may reduce numbers somewhat, though they also catch released parasitoids
- Pull up and dispose of infested annuals and vegetable plants as soon as cropping ends
- Empty and clean the greenhouse between crops: UMass reports a four-week fallow cuts numbers significantly, and even two weeks helps
- Lay reflective mulch under young vegetable plants, and remove it when summer temperatures get high so the plants do not overheat
- Keep ants off infested plants and avoid broad-spectrum sprays, both of which protect whiteflies from their enemies
Chemical, last resort
Contact sprays kill only what they hit — cover the leaf undersides, repeat, and skip broad-spectrum products. Imidacloprid and bifenthrin are highly toxic to beesCheck any product before it goes on. Open the compatibility matrix →
- Insecticidal soapREI 12 h
- Narrow-range oilREI 4 h
- SpirotetramatREI 24 h
- Imidacloprid (soil-applied)REI 12 h
- BifenthrinREI 12 h
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
UC IPM Pest Notes 7401, Whiteflies (M.L. Flint, updated 2015)
UC IPM Pest Management Guidelines: Tomato — Whiteflies (text updated 2013)
UC IPM Pest Management Guidelines: Cucurbits — Whiteflies (treatment table updated 2024)
UC IPM, Relative Toxicities of Insecticides and Miticides Used in Tomatoes to Natural Enemies (2016)
UMass Extension, Whiteflies on Greenhouse Crops (T. Smith, 2012)
UConn Extension IPM, Biological Control of Whiteflies
RHS Advice, Glasshouse whitefly
RHS Advice, Indoor plants: sap-feeding insects
UConn IPM, Scouting for Key Insect and Mite Pests on Key Plants in the Greenhouse (2024)
UF/IFAS Gardening Solutions, Hibiscus
Koppert, En-Strip and Swirski-Mite product pages
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
Suggest a correction →Greenhouse whitefly by crop
The same pest behaves differently on different hosts. Each page below gives the host-specific control, rate and threshold.