Codling Moth & SIT

Dr Jim Walker is part of a team from Plant & Food Research developing a three-pronged assault on codling moth using sterilised insect treatment (SIT), mating disruption and a parasitoid wasp.

Sex pheromones are natural chemicals released by the females of many insect species to attract mates. They can be used to disrupt communication between insects, impeding their ability to identify mates and subsequently leading to a reduction in the population and need for insecticides.

Dr Jim Walker was part of a team at P&FR to develop and successfully trialled a product that disrupted the mating behaviour of codling moth, along with three pest species of leaf roller moths.  The result from this trial was a 70% reduction in insecticide spraying, little or no fruit damage and no residue problems. 

The team identified and isolated pheromones from four species key apple pest species – codling moth, light brown apple moth, green-headed leafroller and brown-headed leafroller. They were then able to develop synthetic pheromones and deliver them to the orchard to disrupt mating of all four species.  

The technology was a key part of the Apple Futures programme that aimed to produce apples for export with ultra-low residues to meet market regulations and supermarket customer assurance programmes.

In a recent survey, New Zealand apples were identified as the cleanest in international markets and now, about 65% of our export apple crops have no detectable insecticide residues.  

Jim Walker says codling moth is the number one pest of apples. He and his team have been part of project piloting the release of sterile codling moth as part of a wider project to reduce chemical use in apple orchards. He says in many of the new, high value Asian markets that are now targeted by NZ apple growers have a zero tolerance for this pest.

The Sterile Insect Technique (or SIT) has been used with Codling moth since 1990s in British Colombia, although its first use in New Zealand was against the painted apple moth in Auckland. It was used as the final step in that successful eradication programme.

SIT is a relatively new weapon against insect pests in New Zealand. It complements the sectors drive for residue free production and is another method of biological control. It is an organically acceptable method that involves releasing large numbers of sterile insects into the environment, “overflooding” the wild population and by providing sterile mates for the existing population there are no viable eggs produced for the next generation to grow from.

The technique is being developed for a range of pests, from citrus pests in South Africa to fruit fly control in Australia, and now apple pests in New Zealand.

Jim Walker says the release of sterile insects, in combination with mating disruption and the parasitoid wasp, is a three-way strategy that looks very promising for long-term suppression of codling moth. He says the SIT in codling moth is very insect specific and there’s potential for long term eradication in localised areas.

Being able to replace traditional chemical methods with new biologically-based controls will further enhance the apple industry’s reputation for pest-free produce with no chemical residues.

The Hawke’s Bay SIT trial:

The sterile insects for the New Zealand trial came from a large production facility in British Columbia, Canada, that provides sterile moths to their industry during their summer. The sterile moths for New Zealand come from their winter production and are then air-freighted here each week and then released to mate with the wild moth in Central Hawkes Bay orchards. Over-flooding the local wild moths means number of viable eggs is greatly reduced.

The Canadian moths were imported with an MPI permit. During the trial, up to 80,000 sterile moths were imported each week. The moths are marked with red food dye to differentiate them from the wild moths. Jim says the moths will typically live for two weeks after release.

The Hawkes Bay pilot project took place on the Ruataniwha plains. They started with 200ha and then expanded to 350 ha. The release rate is 200 moths per ha per week, with 14 to 15 releases per season.

Moths are released using a fixed wing UAV (Unmanned Aerial Vehicle, or drone). The drone allows very efficient delivery of insects, with more than 20,000 moths released across a 100ha orchard in a 10 minute flight.

The orchards where SIT was trialled have already have a high level of control using using mating disruption and insecticides. Prior to the release of the SIT insects Jim says there was reasonably low incidence of codling moth. The season prior to SIT the total orchard wild catch of codling moth was 103 moths. Following the second year release (the first year of effective control) the total catch of moths was 16. Now, after three seasons of SIT they have seen up to a 98% reduction in the catch of ‘wild moths’. Jim says the wild populations on these orchards now are now very close to complete elimination.

Jim say one codling moth in a carton of New Zealand apples arriving in some Asian markets can knock out a whole pathway for export and have a cascading effect from the exporter all the way back to the grower. He says potential economic value of SIT is around $80M per annum. With wider adoption of the SIT, further reductions in insecticide use are possible.

Longer term challenges for releasing sterile codling moth in the wider Hawkes Bay area include: getting sector wide support, elimination of alternative hosts for codling moth, community engagement and support, and CAA approval to overfly urban areas.  

SIT technology is a form of biological control that is organically acceptable and could also be used for future incursions of fruit fly.

Along with the mating disruption, New Zealand and Plant & Food Research scientists have introduced and released the tiny parasitic wasp, Mastrus ridens, a natural enemy of codling moth. More than 60,000 of these parasitoids have been set free into NZ’s main apple growing regions.

The Mastrus wasp is a biological control agent and an important new component in the system of control. The female wasp attacks the cocoons of codling moths, laying its eggs on the moth larvae. When the wasp larvae hatch, they feed on, and eventually kill, the codling moth larva. They then emerge as adult wasps to disperse and seek new codling moth larvae on which to lay their eggs.

Jim Walker says, “Many of our orchards are completely free of codling moth, or the populations have a very, very high level of control, but codling moth exists in walnut trees, and unsprayed quince and apple trees in people’s back gardens and the like, so I guess the industry with foresight (and that from a previous colleague of mine, John Charles) set about to introduce a parasitoid of codling moth as a non-insecticidal method of reducing the codling moth populations out there in our untreated home garden orchards, our wild walnuts, and our wild apples.

What we’re doing through this whole programme, supported by an SFF project through MPI, is now we’ve gone through the EPA process, and got permission, we’ve released more that 60,000 of these parasitoids around the country. We’re now following how well they’re doing and how they’re building up in not our orchards (because there aren’t a lot of codling moth in our orchards now) but in our unsprayed, unmanaged areas of apple trees around our export orchards.

We started to release Mastrus around 2012. It’s been a fairly steady programme, over three years, and now what we are doing is following up to look at how well those parasitoids have established in those areas of release, and more importantly what impact they’re having on codling moth populations.

It’s a perfectly complementary technology. We can treat our orchards with pheromone, we can eliminate codling moth over areas of export production using the sterile insect technique, what we are really trying to do here is have a whole balance approach so that our sources of codling moth that we can’t manage which are really those that are outside the orchard are also under attack by this newly release parasitoid.