Encarsia parasitic wasp

How to recognise it

Under 1 mm with a yellow abdomen - effectively invisible. The sign is whitefly scales that have turned BLACK instead of staying translucent pale.

Mistaken for

Black whitefly scales look like the insect has gone mouldy or died of disease, and people redouble their spraying. In fact black scales mean the wasp is winning.

What it eats

Whitefly

How to attract it

Warmth and no broad-spectrum sprays. In a greenhouse it can be bought and released - one of the oldest and most reliable biological controls there is.

Plants that help

Tomato, Cucumber, Sweet pepper

Lifecycle

Lays into whitefly nymphs; the parasitised nymph blackens and a new wasp emerges through a round hole.

Months: April, May, June, July, August, September, October

The thing people get wrong

Count black scales versus pale ones. Once black outnumbers pale, the infestation is already collapsing on its own - and any spray from that point sets you back weeks by killing the wasps and leaving the surviving whitefly free.