Forage Science

Trials of natural insecticide to fight black beetle underway

2 December 2015
Trials of natural insecticide to fight black beetle underway

Large-scale field trials of a prototype product containing a natural insecticide to fight black beetle are underway following several years of research by AgResearch.

Research into the prototype product, that is infused with the naturally occurring bacterium Yersinia entomophaga (Ye), moved into large-scale field testing which includes investigating the optimum application rate on several sites in Waikato farms.

AgResearch senior scientist Dr Pip Gerard said the prototype had been successful in smaller trials where it had killed adult black beetles.

"This year we have large paddock trials on nine sites. We’ve had some excellent initial results against the adult black beetles in spring and now we are waiting to see if it has stopped them laying eggs and therefore is protecting the pastures against larval attack over summer."

These trials follow work undertaken by senior scientist Dr Michael Wilson in autumn and spring last year that provided encouraging results and suggested that spring might be the optimum time to utilise the product.

“In spring you kill the adults before they lay eggs so you get fewer larvae hatching and it’s actually the larvae that do most of the damage. It’s difficult to target larvae directly with a biopesticide because they are underground, so hitting the adults in spring is probably the way to go,” he says.

AgResearch senior scientist Dr Mark Hurst says that if successful the product would have a significant impact on black beetle populations which cannot be effectively controlled by insecticides in established pasture.

It’s a great example of an effective biopesticide: a natural pesticide based on micro-organisms or their bioactives, targeted and safe for the environment and humans and helping to solve many insect pest and disease problems.

Black beetle (Heteronychus arator) is found in warm areas of the North Island, where root feeding larvae are capable of severe pasture damage. Dry summers and autumns for three years have contributed to a population explosion.

The product is based on the Ye bacterium discovered in 1996 in a grass grub corpse during a search for alternatives to chemical pesticides such as organophosphates, which are being phased out. Ye releases toxins that ‘burst open the gut’ of the insect and cause rapid death, says Dr Hurst, who leads the research on this bacterium.

“The biopesticide is good at killing a large variety of insects, especially beetles and moths. But it doesn’t harm earthworms, honeybees or other beneficial organisms.”

Dr Hurst says that now the product has been proven to work, they will explore the best methods for manufacture and application in existing farm machinery.

Meanwhile, entomologist Sarah Mansfield is investigating the movement and feeding behaviour of black beetles for the most effective delivery technique for the product and to help determine how much of a farm needs to be treated to ensure control.

Next Generation Biopesticides Programme leader Dr Maureen O’Callaghan says all the research points to a user-friendly biopesticide product being much closer.

“The very promising results achieved in the field trials are the result of excellent collaboration between researchers, industry partners and farmers.”

Development of the prototype has been supported by Ballance Agri-Nutrients and MPI via their PGP programme, and DairyNZ.

Enthusiastic Waikato farmers have hosted field trials as part of several Sustainable Farming Fund and DairyNZ projects focussed on controlling pests, O’Callaghan says.

The biopesticide product could be used in combination with other techniques to control black beetle, such as sowing insecticide-coated seed to kill black beetle adults when grass seed is germinating. Farmers can also use ryegrass cultivars containing the endophyte AR37.