Whitefly Control - Encarsia formosa Parasitic Wasp

The whitefly problem is different from most greenhouse pest problems. Adults are inch-sized flying insects, so any sudden movement sends them scattering in a ghostly white cloud only to resettle moments later. Sprays hit the leaves but rarely the flies themselves. Sticky traps catch some but not enough. The population turns from "a few whiteflies on the tomatoes" into "hundreds of whiteflies on everything" in the space of a warm fortnight, because a single female lays 100 to 200 eggs. This is the moment the chemical-free grower reaches for Encarsia formosa — a tiny parasitic wasp used commercially in tomato and cucumber greenhouses since 1926, and one of the most reliable biological controls available for the amateur gardener.

Made by Anthropos and supplied to us directly through our biological control partners at Ladybird Plant Care, one of our trusted collective partners. Live product, shipped from their refrigerated facility to your door at peak freshness.

How Encarsia works

The science is more elegant than it sounds. Encarsia formosa is a parasitic wasp about 0.6mm long — smaller than the whitefly it hunts. Adult female Encarsia locate whitefly scales (the nymph stages, which sit motionless on the underside of leaves) and lay a single egg inside each one. The developing Encarsia larva consumes the whitefly nymph from within. After about 10 days the whitefly scale turns visibly black — the sign that an Encarsia has successfully completed its life cycle inside. From that black scale, a new adult Encarsia emerges, ready to parasitise the next whitefly nymphs. The population shifts, over a few weeks, from mostly whitefly to mostly Encarsia. One Encarsia can parasitise 5 to 10 whitefly nymphs per day, and adult wasps live for about 30 days.

The wasps themselves are essentially invisible in the garden. They pose no risk to humans, pets, plants, pollinators or beneficial insects. They cannot sting. They stay where the whiteflies are — on the plants — and they die naturally once the whitefly population has collapsed and there's nothing left for them to lay eggs in.

Identifying your whitefly correctly

Species matters. Encarsia is highly effective against the common glasshouse whitefly (Trialeurodes vaporariorum) but works less well against tobacco whitefly (Bemisia tabaci). Before ordering, take a moment to confirm you're dealing with the right species:

• Glasshouse whitefly — the common UK greenhouse pest. When looking down at a resting adult, the wings form a heart-shape profile, closed together over the body. This is what Encarsia targets
• Tobacco whitefly — less common in UK gardens. Wings are longer, parallel, and when folded you can still see a strip of body showing between them. Different species, different biological control needed — contact us for advice if you suspect this is what you have
• Not whitefly — if you see white threads sitting static on the tops of leaves rather than flying around, these are shed aphid skins that have dropped from developing aphids above, or thrips larvae. Not whitefly, and Encarsia won't help. Whitefly are nearly always moving, and the body plus wings are a ghostly white

When you'll reach for them

Encarsia are the biological control of choice for warm indoor growing environments where whitefly find ideal conditions:

• Greenhouse tomato and cucumber crops — the classic Encarsia use case. Whitefly love the warm, humid, sheltered environment; Encarsia thrives in the same conditions
• Conservatories with houseplants — fuchsias, poinsettias, aubergines and pepper plants under glass are all prime whitefly targets
• Polytunnels — particularly late spring through summer when temperatures are consistently warm
• Overwintered greenhouse plants — whitefly populations can build up on plants brought inside for winter; Encarsia treatment as spring temperatures rise breaks the cycle before it reaches summer
• Preventative use before infestation takes hold — hanging a couple of cards early in the season, when you first notice a whitefly or two, is far more effective than trying to treat an established outbreak
• Post-quarantine on new plants — whitefly often arrive on newly bought plants; introducing Encarsia to the greenhouse pre-emptively catches any imported eggs before they establish

Choosing your pack size

Cards are supplied with Encarsia pupae attached, ready to hatch and disperse. Pack sizes:

• 5 cards — average conservatory or small greenhouse. The starting size for most home growers
• 10 cards  — larger greenhouse, or the amount to use for an existing outbreak where you want faster suppression
• 20 cards — polytunnels, larger greenhouses, or two-treatment courses (initial + follow-up a week later)
• 50 cards — commercial-scale growing spaces, multiple greenhouse operations, or a full-season treatment plan

For a longstanding whitefly battle, follow the initial introduction with a second one a week later. For low-level whitefly or preventative use, apply every two weeks.

Setting them up

Encarsia work best when the environment is right. A few practical points:

• Temperature above 18-20°C — Encarsia become active above 18-20°C, work best above 21°C, and prefer conditions below 25°C. Below 18°C they're inactive. This means the useful season in most UK greenhouses is mid-March to August
• 12 or more hours of daylight — Encarsia need reasonable day length. Early or late season use is possible with supplementary heating and lighting
• Hang cards on lower branches — slightly shaded positions are ideal; direct sunlight can be too intense for the emerging wasps
• Distribute cards throughout the growing space — don't cluster them all in one corner. Whitefly will be spread across the plants, and the wasps need to find them
• Allow time — wasps emerge over roughly two weeks from the cards. You may not see dramatic reduction for three to four weeks after introduction. This is normal biological control speed

Signs it's working

The clearest visible indicator is black whitefly scales on the underside of leaves. Where you previously had white scales (the whitefly nymphs), you'll increasingly see black scales — each one contains a developing Encarsia. Once the population balance tips, you'll notice fewer adult whiteflies flying around when you disturb the plants, and the honeydew (sticky secretion whitefly drop onto leaves below) will begin to reduce. Full control typically takes 4 to 8 weeks depending on starting population and environmental conditions.

What not to combine with

Encarsia are killed by most chemical insecticides, including systemic ones already in the plant tissue. If you've recently sprayed with a synthetic insecticide, wait at least two weeks before introducing Encarsia. Also avoid:

• Yellow sticky traps during active Encarsia treatment — they'll catch the wasps as well as whiteflies. Remove any traps before releasing Encarsia and don't reintroduce them until treatment is complete
• Any chemical insecticide spray for at least two weeks after release — systemic residues in plant tissue will kill emerging Encarsia. If you feel a chemical intervention is needed alongside biological control, use insecticidal soap or horticultural soap only on badly-infested individual plants, not the whole greenhouse
• Very cold nights early in the season — wait for consistent daytime temperatures above 18-20°C before treatment

About Ladybird Plant Care

Ladybird Plant Care are our biological pest control partners, specialising in live predator and parasite products dispatched at peak freshness from their refrigerated facility direct to your door. They handle the cold chain, timing and dispatch schedule for all Bishy biological control products including this Encarsia, our Aphid Midge, Lacewing Larvae, Ladybirds for Aphids, and the full nematode range. The Bishy Barnabee — our namesake ladybird — sits at the heart of why we work with Ladybird Plant Care: chemical-free, biology-first gardening is genuinely aligned with what we do.

A note on ordering timing

Biological controls are ordered fresh rather than held in stock. This means there is a delay of a few days between placing your order and dispatch. Order by 10am Monday for same-week despatch. Orders placed later in the week ship the following week. This is standard for live biological controls across all UK suppliers; freshness matters more than speed for these products.

Specifications

• Species: Encarsia formosa (parasitic wasp, approximately 0.6mm)
• Target pest: Glasshouse whitefly (Trialeurodes vaporariorum)
• Format: cards with Encarsia pupae attached, ready to emerge and disperse
• Pack sizes: 5, 10, 20, or 50 cards
• Application rate: approximately 5 cards per average conservatory or small greenhouse
• Repeat frequency: initial + follow-up after 1 week for outbreaks; every 2 weeks for prevention
• Temperature range: active above 18-20°C, optimal 21-25°C, requires 12+ hours daylight
• Season of use: mid-March to August (extendable with supplementary heat/light)
• Safety: harmless to humans, pets, plants, pollinators and beneficial insects
• Dispatch: direct from Ladybird Plant Care, order by 10am Monday for same-week despatch

A note on chemical-free gardening: Encarsia is at its most effective as part of an integrated approach. Companion planting with French marigolds (Tagetes patula) around your greenhouse tomatoes has genuine whitefly-repellent effect. Regular light air movement (an open door or small fan) disrupts whitefly settling. And keeping newly-arrived plants in quarantine for a couple of weeks catches whitefly eggs before they enter the main greenhouse. Our companion planting seed range includes marigolds and other beneficial-attracting varieties that work alongside Encarsia to keep whitefly populations low year after year.

Selected pack size of cards with Encarsia formosa pupae attached
Instructions (PDF available from product page)

UPON ARRIVAL:
- Open packaging immediately
- Hang cards in greenhouse/conservatory within 24 hours if possible
- Cards can be held for 1-2 days in a cool (10-15°C) shaded place if needed