9 Aug 2017

High-intensity farming cuts native bees by 90 percent

2:55 pm on 9 August 2017

Native bee numbers tend to drop by about 90 percent when surrounded by high-intensity farming, a study shows.

These native bees, from two different genera, both have full pollen sacs on their legs. The Lasioglossum species (left) is on a native Ranunculus flower, and Leioproctus fulvescens (right) is on an introduced Achillea flower.

New Zealand native bees. The Lasioglossum species, left, and Leioproctus fulvescens. Photo: Jay Iwasaki / University of Otago

The research from the University of Auckland is the first of its kind in New Zealand to look at the relationship between farming and native bee populations.

Scientists planted fields of flowering plants in areas with varies levels of intensive and non-intensive agriculture and studied the insects visiting each site.

They found at plots surrounded by high-intensity agriculture, that native bee numbers were down 90 percent.

The study's author, Jamie Stavert, said the findings were unexpected.

"It's quite surprising how drastically agriculture intensification has changed our wild pollinator communities.

"We definitely expected some decline in diversity and abundance for some of our native species, but not as drastically as what we found."

Native bees do not need pristine native landscapes, but they do need a bit of natural habitat, which is hard to find in high intensity agriculture, Mr Stavert said.

"As soon as that (bit of natural habitat) is lost they completely drop out of the system.

"We're looking at 90 percent plus decreases in native bee abundance when you go from low intensity to high intensity agricultural sites."

He said it was a risky strategy for agriculture to rely on honey bees for crop pollination.

"Honey bees are super vulnerable to disease.

"If for some reason we can no longer use honey bees for pollination then we really need to think seriously about these other wild native pollinators and how we manage the land to allow them to persist and thrive."

Mr Stavert said native bees required bare or undisturbed soil for nesting in and diverse floral resources when they are active, so even small natural patches in the landscape would help maintain numbers.