Parasitic wasps attack pupae

A generation of red admirals is lost

December 2024

Moths and Butterflies of New Zealand Trust (MBNZT) are a charity that grew from the need to preserve monarch overwintering grounds. They have a number of interesting projects and I've been contributing to one - the Red Admiral Project.

Red admirals are endemic to Aotearoa New Zealand and are related to the northern hemisphere red admirals which they resemble. Their Māori name is kahukura - red cloak - and their preferred caterpillar food source is tree nettle, ongaonga.

Red admirals are rare in Auckland for a number of reasons, all to do with us imposing ourselves on the environment in various ways. Down country they are more common. If I pull the observations on iNaturalist for the last year, 468 were recorded across the country, including the subspecies on the Chatham Islands.

The parasitic wasps are tiny and easily overlooked

In order to try to build numbers back in Auckland, the Trust has several members breeding them, whilst others, such as myself, raise them on from eggs or caterpillars.

My first red admiral butterflies emerged in late November / beginning of December, but I did have some problems. I haven't raised red admirals before, but I have raised some yellow admirals and a lot of monarchs. At the old house the caterpillar castles sat on tables on a covered deck, so they had protection from the elements, whilst not subjecting them to the false environment of inside a house. Here I don't have that covered space, but I thought the courtyard on the west side looked well-protected. Unfortunately, despite a 6 foot fence, the winds tend to swirl around and they knocked down the castles I had put on a trestle table, despite the weight inside them. I believe this damaged some of the pupae as they didn't emerge. However, 10 did eclose and I set them free.

Red admiral butterfly, endemic to Aotearoa New Zealand

After Christmas I found out why I hadn't had any more butterflies emerge. I found chrysalises with holes in them like in the photo below. This is the exit hole the wasp creates to escape the pupa. The female wasp lays eggs in the caterpillar whilst it is J'ing, that is hanging in a J shape ahead of turning into a chrysalis. The wasp larvae then eat the pupa alive. Those who have raised a lot of admirals say you can tell from the colour of the pupae if they have been parasitised. Being new to raising them, I couldn't tell.

This happened even with the caterpillars protected in castles made of insect netting. The wasps either found tiny holes in the netting or got in between a gap in the dual zips. I don't think they got in when I was putting new nettle in, as I'm interested in insects generally and I think I would have noticed something in flight, even if small.

I was able to capture some of the wasps, but not able to get them identified. This could be Pteromalus puparum, which was introduced into New Zealand to reduce cabbage white butterflies, which target export crops. As in the United States, the wasps found the native butterflies were just as useful for reproduction. It frustrates me that time after time New Zealand has chosen to introduce predators to help our industries or to solve a problem of something else introduced, only for it to have a detrimental effect on something completely different. I know with testing nowadays it can be years before something is introduced, but the history of these introductions has made me very weary of the whole process.

Wasp in the Family Pteromalidae

Losing so many red admirals has been upsetting and with the earlier losses, it's a big hit. I only hope that I can learn from the problems and that future generations of red admirals will be healthy and help re-populate the Auckland area.