The wasp problem at Bushy Park Tarapuruhi

Bushy Park Tarapuruhi is a 99-hectare forest reserve about 24 km from Whanganui, cared for by Forest & Bird and the Bushy Park Trust. In 2005 a pest-proof fence was finished around it. Toutouwai (North Island robins) had been returned in 2000 and tīeke (saddleback) followed in 2006. Both feed mostly on insects and other invertebrates.

The invader the fence can't stop

Introduced wasps fly straight over fences. German wasps arrived in NZ in the 1940s and common wasps later. With no natural enemies and mild winters, their numbers can explode. In some NZ forests in late summer, wasps weigh more than all the birds, rats and stoats put together. They eat huge numbers of caterpillars, spiders and other invertebrates, the same food robins and saddleback feed their chicks.

Traps or bait?

People often hang sugary lure traps and count the dead wasps. Research shows these traps don't reduce wasp numbers across a forest: each worker killed is quickly replaced from the nest, and the traps also catch native moths, flies and wētā. That is a problem in a reserve built to protect native insects.

Protein bait works differently. Worker wasps carry the bait home and share it with the whole nest, so the colony, including the queen, dies. In DOC trials at five South Island sites in 2015, a single round of protein baiting cut wasp activity by about 96% on average, and a month later almost no wasps were left at some sites. The bait sits in stations on tree trunks, designed so that wasps can reach it but other animals can't.

Where students fit in

A school STEM project with Bushy Park looked at designing bait-station housings that could be 3D printed locally. The housing holds no poison itself; its job is to shelter the bait tray and keep non-target animals out. Every design choice, from hole size to roof shape, is a science question.

Thinking like an ecologist

Counting dead wasps measures effort, not success. To know whether a method works, you have to measure what you care about, such as wasp activity or insect numbers, before and after, in treated and untreated places.