Cocoons on Brassicas

If you come across a cluster of small, yellow cocoons on leaves of Brassica vegetables – don’t spray them or feed them to the chooks. They do not belong to garden pests. (See photos below.)
These cocoons are, in fact, the pupation stage of a very small, black wasp. This wasp belongs to the Braconidae family. Braconids are parasitic wasps and very beneficial insects to have in your garden.
The female adult wasps, which are barely 5 mm long, lay their eggs in caterpillars of the Cabbage White Butterfly, which feeds on the leaves of stressed broccoli, Brussels sprouts, cabbage, cauliflower, horseradish, kale, radish, rocket, swedes and turnips.
The wasp larvae then feed on the caterpillars from the inside until they are ready to pupate. (Sounds gruesome, doesn’t it.)
They each then spin a small cocoon on the remains of the caterpillar, and hatch out two or three weeks later to repeat the cycle.
Adult wasps feed on nectar from flowers. It is worthwhile growing some nectar-producing plants to encourage these useful pest predators.
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5 Replies to “Cocoons on Brassicas”

  1. So cool — I’d just taken photos of these on a flowering broccoli in order to have someone on the Net identify them! I did wonder if it might be the parasitic wasp, as there was a very crook-looking cabbage white caterpillar next to each group of pupae, but I couldn’t work out what was happening. I’ll keep checking the little fellas to see when they hatch.

  2. Hi, I have found the exact same thing hanging on my veranda down low, I didn’t no what they were so I searched them on the internet and then i found this so what do i do. I don’t have a garden either and i only found them yesterday and i have no idea when they will hatch… please help me. Thank you Tiarna πŸ™‚
    Wait and see what hatches from the cocoon before taking any action. – Lyn

  3. So thankful for the photos. I have tried all combinations of words trying to get a hit on google about them…and then, like magic, there they are.

    I have left japanese mustard spinach, rocket, etc to go to seed and have been enjoying the many ladybugs that have come to call my garden home. The cabbage moth caterpillars seem to like the spinach plant, too (the flowers and seeds look just like a turnip does when it goes to seed). I had no idea what the little yellow bundles were.

    I will definitely take care of these now as my birds can only eat so many of those big fat green caterpillars that decimate the brassicas.

    Once again, thankyou, thankyou.
    Kerri

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