Teen's bug work casts a new light

The tradescantia leaf beetle up close.

A Kerikeri teenager's world-first research is shedding new light on a Brazilian leaf beetle controlling a widespread pest plant in Northland.

The plant, called wandering jew or wandering willy has the botanical name tradescantia, has been under attack since the little beetle with the big name - Neolema ogloblini or tradescantia leaf beetles - was introduced several years ago.

Aimee Leaming with a tradescantia beetle.

The hardy, shade-tolerant pest plant thrives in Northland's relatively mild, semi-tropical climate and forms thick blankets that can smother and exclude virtually all other plant species.

Aimee Leaming took out a Northland Regional Council (NRC) excellence award at the recent Far North Science and Technology Fair for her study into the beetle's survival and feeding rates.

The Kerikeri High School Year 13 student studied light intensity and temperature preferences, and established a population of beetles in Kerikeri for her research.

Aimee's work - including a series of intricate dissections of the tiny insects - showed that while they are suited to Northland, they may struggle in cooler parts. New Zealand is understood to be the first country to introduce tradescantia beetles as a biocontrol.

Aimee's observations, including the beetle's fondness for dappled light, will offer valuable insights for researchers deciding where to release them in future.

The relative lack of information about the beetles is probably because in their native Brazil, tradescantia weed is not invasive, she said. It was the lack of information that triggered her own interest.

Most of the research done by New Zealand scientists before the beetle's 2011 release in Northland had been to make sure it was host-specific and posed no risk to other plant species.

The species Aimee studied is informally known to researchers as "shiny" due to its dark metallic bronze colour and slight iridescence.

However, since 2011 two more species had been released in Northland - a stem borer nicknamed "knobbly" and a tip feeder dubbed "stripey", due to their respective markings.

NRC entomologist Jenny Dymock said Aimee's research is impressive and potentially has international implications. Dr Dymock said biocontrols like the beetles offer cost-effective pest control which doesn't require the use of herbicides or other chemicals.

"While biocontrols aren't in themselves a 'magic bullet' solution to pest species, they're a smart tool for today's world." Biocontrol agents at work in Northland included insects, fungi and rusts attacking tropical grass, webworm, mistflower, gorse, ragwort and tobacco weed.