Whangarei fruit fly find a worry

In early April 2014, a solitary male Queensland fruit fly (Bactrocera tryoni) was found in a biosecurity surveillance trap in the Parihaka area of Whangarei. The find had biosecurity authorities on alert and resulted in immediate restriction on the movement of fruit and vegetables for a 1.5 km radius.

Of concern was that the fly was found just 400 m from where another fly was trapped in January 2014, although the Ministry for Primary Industries (MPI) issued a statement saying that their best information suggests the two finds were unrelated separate incidents. “In both cases the solitary flies were the only detections and no breeding populations were found in the area.”

Finding two flies like this is very rare. A fly was also trapped in May 2012, and prior to this, there had not been a Queensland fruit fly detection in New Zealand for 16 years. In 2019 ten fruit flies were discovered.

The fly, a native of Australia, is of huge concern to New Zealand’s horticultural industry and home gardeners. In Australia, the fly is considered to be the country’s most serious insect pest of fruit and vegetable crops, attacking over 100 varieties of fruit, including avocados, citrus, feijoas, grapes, peppers, persimmons, pip fruit and stone fruit.

Fruit fly life cycle

Like many insects, the species has a four-stage life cycle. The adult females puncture ripe fruit to lay their small white banana-shaped eggs in the cavity. When the maggots (aka larvae) hatch out, the squirmy critters eat their way towards the centre of the fruit, often causing it to rot from the inside, although the fruit may appear to be OK from the outside. One apple or peach might support as many as 40 maggots.

When the maggot finishes growing, it chews its way out and usually falls to the ground, where it burrows into the soil to complete its pupa stage. An adult fly hatches from the pupa after it has become hard and brown. After hatching, it usually feeds on juice from the host plant, nectar and honeydew secreted by other insects.

The whole life cycle from egg to adult might take anywhere from 2 weeks to 2 months depending on the season. They do not breed in winter and survive the season in the adult stage. The adult female can live for almost a year, and several generations can exist concurrently.

The species is found in parts of the Northern Territory, the eastern areas of Queensland and New South Wales and the extreme east of Victoria. Queensland fruit flies have also been found on Pacific islands such as New Caledonia, French Polynesia and Pitcairn Islands as a result of human activity.

Checking traps and fruit for fruit flies

According to the statement from MPI, personnel were in the field within hours of identification of the fly, setting up an extensive network of traps to ascertain if a breeding population was in the area. Laboratory staff also analysed hundreds of kilos of fruit, checking for the presence of fruit fly larvae.

“MPI’s fruit fly response field work is carried out to a guiding document known as a Response Standard which reflects international best practice and is approved by international experts. This specifies that the response traps and movement controls on produce must be in place for a full 14 days with no [further] fruit fly detections.”

Concerns about managing biosecurity risks

In a press release from HortNZ, Chief Executive Peter Silcock said that, while he is happy with MPI’s actions over the find, he is concerned about how we are managing the biosecurity risk in the first place.

“We have confidence in our system to detect any fruit fly at a very early stage and this system is critical for maintaining international market access for our products,” he says.

“But we do have to urgently look at how we are managing the biosecurity risk, so we don’t keep finding this pest in our traps.”

“This is a pest that we don’t want because it will impact on our ability to grow things, export produce and on the 50,000 jobs this industry provides across New Zealand."

It is in everyone’s interest to keep this pest out.

In an article Mr Silcock wrote for industry group Summerfruit New Zealand, he was even more hard hitting: “The risk to New Zealand horticulture from pest and disease incursions is so great, so significant, and so costly, it has growers breaking out in a cold sweat. The problem with biosecurity is that it is a numbers game. It is all about risk.”

Potential biosecurity risks up to 25 times per day

“MPI Biosecurity knows there are roughly 25 detections of undeclared potentially fruit fly carrying materials at the New Zealand border every day − about 9,000 every year,” Mr Silcock continued. “That is the risk horticulture lives with. The potential is there, 25 times a day, for a Queensland fruit fly to find a home in New Zealand as it does on a regular basis in the supposedly fruit fly free regions of Tasmania, South Australia and NSW.”

The restrictions meant that whole fresh fruit and vegetables (except for leafy vegetables and root veges) could not be moved outside of the controlled area. The restriction lasted until 20 April 2014, when authorities had decided the find was an isolated incident. However, they continue to set and monitor lure-based surveillance traps. “Some 7,500 traps are located throughout the North and South Islands and are concentrated in populated areas serving as centres for tourism and/or trade, areas of significant horticultural activity and areas specified as being climatically conducive to the establishment of fruit fly,” says the MPI website.

February 2019 return

Feburary 2019, a male Queensland fruit fly was detected in the Auckland suburb of Northcote, triggering another biosecurity response. During this biosecurity operation nearly 6,000 homes were placed under controls that restricted the movement of certain produce, one-and-a-half tonnes of fruit were collected from the area and inspected and in addition an intensive baiting programme was run throughout the spring. Biosecurity New Zealand spokesperson Dr Duthie said in that total, 10 male flies were detected, but no evidence of a breeding population was discovered. After six months with no more fruit flies being detected, Biosecurity New Zealand announced in January 2020 that the biosecurity operation was ended. The nationwide routine surveillance programme continues as usual.