Posted by Zane McGrath

For the remainder of these summer months I will be searching far and wide for the kawakawa plant. It isn’t the odour emitted by its heart shaped leaves or berries I am attracted to, but the caterpillars hosted by the plant, which I will attempt to adopt and take back to their new home, the luxurious lab at Landcare Research. Although in highlighting the beauty of ecological research, and just to make things more confusing (see earlier posts by Sam and Carolina on ecological complexity), it is not the plant or the caterpillars that will be the main focus of my Masters research, but parasitoid wasps which emerge from the caterpillars.

The kawakawa plant (top) and kawakawa caterpillar (bottom)

Parasitoid wasps spend part of their life cycle within a host, such as a caterpillar, and basically eat their way out when ready to pupate, eventually killing the host. Fascinating or down right freaky (have a look for yourself in this video), parasitoid wasps have the ability to act as natural enemies for controlling agricultural pests. For my Masters research I will be focusing on whether Meteorus pulchricornis, a species accidentally introduced into New Zealand, is competing with native species for caterpillar hosts.

The culprit, Meteorus pulchricornis (Photo: iNaturalist.org) (top) and its cocoon hanging from a kawakawa plant, which is unique to the species (bottom)

In order to understand this, the caterpillars I collect will be reared until they reach their fate. If I’m lucky, but the caterpillar isn’t, a parasitoid wasp will emerge.

This is where I must hone my husbandry skills. The caterpillars can grow considerably over the period of a month or so before pupating. They will be fed their favourite meal, a kawakawa leaf that is replaced every five to seven days. However, as a parent would say, the growing up process isn’t always a pretty sight. Their homes can become inundated in frass (caterpillar poo), and need I say the larger the caterpillar grows, the larger the frass… but hey, it’s all part of being a parent.

Frass and a caterpillar

Zane McGrath is an MSc student in the Centre of Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. He is supervised by Darren Ward and Graham Walker (Plant and Food Research, Auckland) examining parasitism by exotic species in native environments.