This pest-busting wasp has saved $488m

A weevil-killing wasp imported to New Zealand is estimated to have saved the economy half a billion dollars. Photo / AgResearch

New Zealand has been spared half a billion dollars in damage from a notorious pest - and scientists say it's an Irish wasp we have to thank for it.

While wasps are often discussed as a troublesome pest themselves, one particular species has proven itself effective at combating the highly destructive root weevil.

The weevil, first detected in New Zealand in 1996, is an invasive pest from the northern hemisphere that feeds on clover and one study estimated that without control, the pest could could cut farm margins by 10 to 15 per cent.

AgResearch responded by importing the Irish wasp as part of a wider biological programme that, since 2006, has brought an estimated $489 million in benefits based off reduced production losses on sheep and beef farms, and reduced use of urea fertiliser to compensate for damage from the weevil.

The wasp injects its eggs in the adult root weevil, and the resulting grubs inside the weevil render it infertile.

Once fully grown, the grub kills the weevil as it eats its way out - one wasp can kill about 85 clover root weevils.

After the wasp was brought to Kiwi farms in controlled releases around the country, it was so successful that it slashed weevil populations by around 90 per cent in monitored areas where the wasp is well established.

The work has more than paid for itself: research and development costs have come to about $8.2 million - and its benefits continue at an ongoing rate of at least $158 million per year.

"It's a fantastic example of how our science is making a real and profound difference to our agricultural sector and economy," AgResearch science team leader Dr Alison Popay said.

"It's also a real success story in the continuing battle against pests on New Zealand's farms."

Another breakthrough

Meanwhile, scientists have also reported some good news with a breakthrough against another scourge: the hive-destroying disease Nosema ceranae.

This relative newcomer to New Zealand is a cousin of Nosema apis, which has been present in the country since the 1800s.

Both N. apis and N. ceranae are spore-producing parasites that attack the gut lining of bees, leading to a shortened lifespan in adults, and severe cases of N.ceranae may cause the collapse of an entire colony.

Because it's primarily spread through faeces on contaminated honeycomb, preventing infection is a near-impossible task, meaning the commercial costs associated with Nosema infection have become seen as a fact of life.

During the springs of 2014 and 2015 many New Zealand beekeepers, particularly in the Coromandel, experienced severe and unexplained colony losses - a pattern that had not been seen before and which resulted in honey loss estimated at between 40 to 60 per cent for the season.

N. ceranae had first been found in New Zealand in 2010 and was identified as a potential culprit for the calamity.

In response, a team from Plant and Food Research began working closely with Coromandel beekeeper Dr Oksana Borowik - first confirming high levels of N. ceranae in affected colonies, and then exploring ways to prevent the spread of the disease between hives.

Their early research findings were exciting: heat-treating the hive and internal comb to only 50C for 90 minutes resulted in an increase in brood viability and a 50 per cent increase in adult bee numbers.

The treatment is effective because heat kills N. ceranae spores lurking on contaminated comb before the new colony is introduced to the hive.

"Nosema ceranae has had a notable impact on hives and the honey industry in countries like the United States and China," Plant and Food Research scientist Dr Mark Goodwin said.

"We need to take the threat of this disease very seriously, particularly as the honey industry and the pollination services of honey bees are very important to New Zealand's economy.

"The initial findings of this research are a very encouraging first step in the fight against this threat."

The team will build on this initial study with further investigations into the effect of seasonality and long-term treatment on bee populations.

If heat treatment was found to be a safe and consistent management option for beekeepers plagued by Nosema, there was the potential to greatly improve the health and productivity of New Zealand beehives.

Clover Root Weevil

• A major and widespread pest of clovers, both red and white cultivars but white clover often most severely attacked
• Adults feed on clover foliage leaving distinctive notches on leaf margins, but larvae are most the damaging stage, destroying clover roots and root nodules.
• Infested pastures become clover deficient. Biological control has significantly reduced impact of this pest.

Nosema ceranae

• A disease of the digestive tract in honeybees that affects adult bees only and is highly infectious.
• Nosema increases the mortality of adult bees and can cause the death of some colonies during winter and spring.
• Reduces honey yields, and causes poor population build up because the bees are unable to produce enough brood food.
• In slight infection, losses are small, but in severe infections the colony will dwindle and may ultimately die out.

- Source: AgResearch/Ministry for Primary Industries