Māori nailed it: Kaiwētā is a tree on which wētā feast

Friday, 23 October 2020

Two male tree weta. Maori applied the same name to all tree-inhabiting weta.

It probably won’t surprise many that the tree named kaiwētā is a native tree eaten by wētā insects.

But now scientists have used a “two-eyed” approach to understand the relationships between the trees, the wētā, a caterpillar moth, regional ecologies and dialects to provide “comprehensive information about regional plant-insect interactions in New Zealand forests”.

It may not be the first time an examination of Māori language has provided ecological insight, but it may have drilled deeper into the relationships than most.

Researchers led by Priscilla Wehi of Massey University and Manaaki Whenua Landcare Research started with the various names Māori use for the tree, including kaiwētā, but also putawētā and putaputawētā.

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“Puta” in this context means to emerge and the double use adds emphasis, suggesting lots and lots of emergences, Wehi and colleagues wrote.

There was probably a strong link between the names and the ecology but how did the “one eye” of Indigenous Knowledge line up with the other eye of experimental data and observation?

Fieldwork in the North Island showed that a caterpillar moth called pūriri (pepetuna, Aenetus virescens) bored into the trunk of the trees. These holes were later occupied by wētā from which they emerged at night to feast on the same trees.

But on the South Island, where the moth is absent and the tree wētā much less common, the tree is known by a different name, piripiriwhata and some variants. Piripiri refers to hanging ferns and whata, to being suspended.

Having established a North Island relationship between the insect and tree, Wehi and colleagues Gretchen Brownstein and Mary Morgan-Richards dug deeper into the ecology by bringing wētā back to their lab and feeding them kaiwētā leaves and fruit.

The insects were sexed, weighed, measured and their poop analysed. In some cases, the seeds in the fruit were counted and later the seeds found in the poop were counted. The researchers also tried to germinate the seeds that passed through wētā guts. Much statistical analysis followed.

They found that on average wētā ate about 700 mm2 of leaf per gram of body weight per night. From field work, they estimated eight wētā were feeding on each kaiwētā tree per night and the trees were losing about 22 leaves per tree per night.

About 10 per cent of the seeds passed through the guts were undamaged and few germinated afterwards. So yeah, wētā have a massive association with the tree in the North Island.

There was a “considerable loss of foliage” and “we did not detect a direct benefit to the tree from this association”, the researchers found.

“Kai wētā is thus an apt description of the role of this tree species in the forest,” they concluded.

The researcher hope “people will think more deeply about [Māori] place names and the names of our plants and animals, and the ecological information revealed in those names” as result of this research.

This hope extends overseas. It’s thought 80 per cent of the world’s biodiversity occurs on lands managed by Indigenous peoples.

“As such, conservation partnerships that weave Indigenous Knowledge with quantitative data provide a valuable approach that could not only improve understanding of species interactions and ecological systems, but also add value to conservation planning and practice.

“Many conservation decision-making processes, for example, require distributional data that may be embedded in Indigenous Knowledge,” the researchers said.

In English, the tree is called marble leaf and to science as Carpodetus serratus.