Dacnusa sibirica

How it works

The female lays an egg inside a leafminer larva. She can use any larval stage but prefers first and second instars, which is why she works early, before mines are obvious. The leafminer keeps feeding and pupates, and the wasp larva develops inside it and pupates within the leafminer's pupa. The adult chews its way out of the pupal case. Biobest gives 40–200 eggs per female, and Koppert says she can tell parasitised larvae from unparasitised ones. Koppert also says she has more difficulty with L. trifolii larvae than with tomato leafminer, though she develops in both.

Because the leafminer finishes its mine before it dies, a working release looks like nothing at all: Koppert says parasitism cannot be seen from outside without dissecting larvae or pupae. The benefit shows later, as fewer new mines. Koppert rates it more effective than Diglyphus at lower temperatures and advises combining the two when infestations are heavier or the weather warms. Koppert gives two figures: Dacnusa is more effective than Diglyphus below 68 °F (20 °C), and above 77 °F (25 °C) Diglyphus may be the better choice. Koppert also notes that it can turn up on its own in greenhouses in any season.

Is it established?

There is no visible sign on the leaf: Koppert says parasitism can only be confirmed by dissecting larvae or pupae. The practical read is fewer new mines over the following weeks.

1. WEEKS 1–3Weekly releases — at least three (Koppert), three to five (Biobest); nothing visible yet
2. CONFIRMDissect a few larvae or pupae under a lens — the only way to see the wasp (Koppert)
3. AFTERFewer new mines appearing on the plants you check each week
4. IF WARMINGAdd Diglyphus isaea as temperatures and leafminer numbers rise