Brazilian beetle baby boom at Botanic Garden

30 June 2015

Tradescantia – more commonly known as wandering willie – is a depressing, suppressing pest plant. It’s pretty much out of control in public reserves and private gardens all over the country. But Wellington City Council has called in a whole lot of helpers – from Brazil, no less – to take on this invasive weed.

Tradescantia beetle.

Staff at the Botanic Garden are lovingly raising hundreds of Neolema ogloblini – tradescantia leaf beetles – that have been introduced into New Zealand in the hope that they’ll devour wandering willie and reduce the damage it’s doing to our native bush and reserves.

Wandering willie forms thick blankets that can smother low growing plants and prevents regeneration of native bush. It can also cause dermatitis or allergic reaction in dogs.

So far things are looking promising. The beetles are happily breeding in controlled conditions at the Botanic Gardens and they are already attacking wandering willie at a number of trial sites around the city.

The Council’s Biosecurity Technical Adviser, Illona Keenan, says wandering willie is a plant native to Brazil and Argentina and so are the beetles. “Back home in Brazil the beetles feed only on wandering willie – they live for the stuff – and they’re loving the plant here too. So much so that the cultivated wandering willie in Botanic Garden’s glasshouse is looking very munted indeed. We’re very excited.”

Three species of beetle – including the leaf beetle - were introduced to New Zealand in 2011 by Landcare Research to combat tradescantia after approval by the Environmental Protection Authority.

The beetles have been released at sites around the country. Only one species of beetle have been released at each site to monitor the effect each has individually. There are plans to eventually release all three at one site. 

The leaf beetles have already been spectacularly successful in a trial at Kerikeri, in Northland, where leaves on wandering willie have been stripped bare by the larvae, and the rest were well-chewed by the adult beetles.

Illona says the hope is that the leaf beetles will breed freely “in the wild” in the Wellington area and steadily spread to the benefit of private land owners as well as the regenerating bush in the region. “Any gardener will tell you how it’s almost impossible to get rid of wandering willie, even if you hammer it with herbicides, so we are looking forward to our little Brazilian friends doing what comes naturally – and knocking back this horrible plant.”

The beetles will be on display – tearing into wandering willie – in terrariums at the Botanic Garden Treehouse during the Spring Festival. Come along and cheer them on!