Encarsia formosa
A 0.6 mm parasitoid wasp, black with a yellow abdomen, that lays its eggs inside the scale-like nymphs of greenhouse whitefly. A parasitised scale turns black about halfway through the wasp's development, so a working release is easy to read. It is sold as pupae glued to cards, hung weekly in greenhouse crops, and it also kills young whitefly nymphs outright by feeding on them.
At a glance
- Mode
- Parasitoid, plus host feeding
- Rate
- 1–10 /m² per release, weekly until control is achieved
- Ships as
- Black pupae glued to cards
- Temp
- 20–26 °C best; needs a 17 °C average
- Humidity
- 50–80 % RH
- Setting
- Greenhouse only; not outdoors
How it works
The female lays in the older nymphs, preferring third and young fourth instars. Smaller nymphs she feeds on instead, killing them without leaving an egg. Almost every wasp is female — Encarsia formosa reproduces without mating, and males are rare. Estimates of lifetime output vary widely: suppliers quote up to 200 eggs, while one laboratory study recorded 59.
About halfway through the wasp's development the greenhouse whitefly scale turns black; the adult wasp leaves through a round or oval hole, where a healthy whitefly leaves a T-shaped split. Egg to adult takes about 25 days at 21 °C. On tobacco whitefly the parasitised scale turns brownish rather than black, and control of that species is weaker.
Is it established?
Black scales are the sign to count. Turn over lower and middle leaves near the cards and compare black scales with pale ones.
- WEEK 1Wasps emerge from the cards through small round holes over about a week
- WEEKS 2–3First black scales among the pale ones on older leaves near the cards
- WEEKS 3–4Round exit holes in black scales — the first home-bred wasps are out
- TARGET80–90 % of scales black; releases can then stop
Release & handling
Pupae come glued to perforated card strips — 60 per card in Koppert's En-Strip 3,000. Hang them as soon as they arrive. Koppert allows one to two days at 8–10 °C in the dark; Arbico says use within 18 hours and do not store; Rincon-Vitova allows up to two weeks at 5–10 °C but warns emergence falls. Tear the cards apart and hang them in the shade, low in the crop, where irrigation will not wet them.
Hang the same day
Separate the cards at the perforations without knocking the pupae off.
8–10 °C, dark
One to two days (Koppert). Sources differ on longer holding; emergence drops with time.
Shade, off the water
Hang from lower leaves or branches out of direct sun, spread evenly or next to known patches.
Take yellow cards down
Remove them before release and put them back 3–4 days later (UConn), or they catch the wasps.
Pesticide sensitivity
Very sensitive to sprays and to dried residues, including pyriproxyfen, spinosad, chlorfenapyr, acetamiprid and pyridaben (UMass). UC IPM names carbaryl, pyrethroids and imidacloprid as particularly disruptive to whitefly natural enemies. Check a product →
When to choose something else
Encarsia is a greenhouse-whitefly tool for long, warm crops. Choose something else when:
- The whitefly is Bemisia (tobacco or silverleaf whitefly), especially on poinsettia — UMass recommends Eretmocerus eremicus there
- The crop is short — UMass rates it most effective in crops grown for more than four months
- The tomato variety is very hairy — the hairs hamper searching and egg-laying
- The house averages below 17 °C — Koppert says control may be insufficient, and UConn says adults do not fly below 65 °F (about 18 °C)
- You are outdoors — UC IPM says Encarsia is not generally recommended for outdoor use
Where to buy
Suppliers listed alphabetically, not ranked. helpfulbugs takes no commission and does not sell insects.
- Arbico Organics1,000 / 3,000 / 5,000US
- Bioline (Encarline)3,000 / 6,000 / 15,000UK / EU
- Buglogical5,000 / 7,500 / 15,000US
- Koppert (En-Strip)3,000 / 7,500 / 15,000GLOBAL
Encarsia formosa by target
Rate and timing differ by what you are releasing it against. Each page below is the program for one pest.