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Codling moth damage

How are codling moths sterilised?

The moths are treated with controlled low dose gamma irradiation to sterilise the adult moths. The irradiation prevents viable offspring being produced.  If a wild male moth mates with a sterile female moth or a sterile male moth mates with a wild female moth, no viable offspring are produced.  The wild-sterile matings produce either unfertilised eggs that fail to hatch or sterile offspring.   Similar technology is used to produce sterile fruit fly which are currently produced and released in Australia to combat this pest.

Where are the sterile moths produced?

The sterile moths are produced by the Okanagan-Kootenay Sterile Insect Release (OKSIR) program in British Columbia, Canada.  Each year, OKSIR produces around 220 million sterile codling moths, which are released into commercial orchards in Canada every week during the growing season.

New Zealand have been importing sterile codling moths from OKSIR since 2014 for release into commercial orchards. In both Canada and New Zealand, codling moth numbers have been reduced by over 90% in regions where sterile moths have been released.

How does releasing sterile moths reduce codling moth populations?

It’s a numbers game. Releasing a large number of sterile moths into an orchard reduces the chance of wild moths mating with each other. Instead, it increases the likelihood that wild moths will mate with sterile moths. With less mating between wild moths, fewer viable offspring are produced. Over several seasons, the population should signficantly decline.

Codling moth population graphic

The  sterile moths marked with red dye outnumber the wild moths.  This makes it more likely that a wild moth will mate with a sterile moth.

Are the sterile moths radioactive?

No. Just as a person is not radioactive after receiving a medical x-ray, codling moths receiving a sterilizing dose of radiation are not radioactive and safe to release into the environment. Gamma rays are similar to X-Rays but have a different energy level and wavelength.  The source of the gamma radiation used in the OKSIR facility is Cobalt-60. Gamma radiation is used widely in industry and medicine, including sterilisation of equipment and radiation therapy for cancer.

Are the sterile moths a GMO?

No.  The process of sterilisation causes DNA damage to the moth chromosome, but the moth itself is not a genetically modified organism. Sterile insects, including sterile codling moths, are released as part of area-wide pest control programs in certified organic orchards in many countries.

Can sterile codling moths reproduce?

The dose of irradiation (200 Gy) applied completely sterilises the female moths and produces a high level of sterility in the male moths so that very few viable offspring are produced from wild-sterile matings.

How can I tell the difference between a wild and sterile codling moth?

In the rearing facility, codling moth larvae (caterpillar) are fed a diet containing red food dye. This red dye remains in their bodies as adults. Squashing a sterile moth releases the bright red body contents so that they are easily distinguished from wild moths.

Do wild females still lay eggs after mating with a sterile male?

Yes, the female can still lay eggs but these either don’t hatch or produce sterile offspring.

Could codling moths shipped from the OKSIR insectary be contaminated with other insects or mites?

The OKSIR insectary is maintained under strict sanitary protocols and constantly inspected for product quality assurance. In addition, the procedure for collecting the moths from the emergence room requires the moths to fly to a specific UV light source. This procedure not only ensures that moths shipped from the OKSIR insectary are able to fly, it also is a behavioural barrier that would prevent the collection of most insects/mites that can infest poorly maintained facilities. After the moths have been collected, they are inspected again as they are loaded into the containers for irradiation and transport. A final safeguard to eliminate any possible viable insect/mite contaminants is the irradiation procedure which would sterilize the contaminant, because most insects/mites are much more susceptible to radiation treatment than moth species.

Where are the sterile codling moths being released?

The sterile codling moths are being released in selected blocks in three orchards in the Huon Valley. The study is a pilot study to assess the economic, environmental and social benefits of a sterile codling moth release program.  If successful, it will be expanded to include other apple growing regions of Australia.

Will the sterile moths spread to my orchard nearby?

The release sites in Tasmania have been chosen so that there is a large buffer between them and other commercial orchards. Pheromone traps in both the release orchards and adjacent orchards are monitored weekly for codling moths, both wild and sterile.

How many sterile codling moths are being released?

Sterile codling moths imported from OKSIR are being released at three trial sites. The release rate in treatment blocks is up to 6,000 moths per hectare per week (up to 3,000 male moths per hectare per week), from late October through to mid-February each year.

How long do the sterile moths live for?

Codling moths in the orchard live for up to three weeks depending on temperature and other environmental conditions.

Are both male and female sterile moths imported and released?

Yes, both sterile male and sterile female moths are released.  There is no cost-effective way to separate male and female moths on a commercial scale.

Does a female codling moth mate multiple-times or just once?

In an orchard situation, female moths commonly mate 2- 3 times.

Can I still export my apples to protocol markets if I am using SIT to manage codling moth?

Detecting sterile codling moths in a registered export block poses no risk to importing countries.   The Australian Government Department of Agriculture, Fisheries and Forestry has confirmed that any sterile codling moths caught on an export block monitoring trap do not count towards suspension thresholds.

How many eggs does a codling moth lay?

The adult female codling moth typically oviposit 50-100 eggs, about the size of a pinhead, on the surface of the leaves, fruit or spurs when the average temperature is over 15 degrees in spring and early summer.

Codling moth eggs hatch after 10 days and the small caterpillars (larvae) emerge to feed on the leaf surface and make their way to the fruit. They burrow into the fruit and head for the core. They will spend about three to five weeks inside the fruit feeding and putting on body mass until they are ready to emerge and find a place to pupate. By this time they are about 20mm long and cream to pink in colour.

What damage does a codling moth do to apples?

Codling moth larvae cause two types of damage. The first larvae to reach fruit often feed on the surface of the fruit before finding a site into which to tunnel. This initial feeding results in shallow excavated areas, which can become scarred or deformed.  The second type of damage is when the larvae tunnel and excavate as they feed their way towards the core of the apple.  Once they reach the core they feed on the seeds. Often the fruit flesh around these tunnels is broken down by bacteria and the tunnels are plugged by the insects using excreta (frass), which can be seen exuding from the entry hole. As the larvae leave the fruit they again tunnel through the flesh to reach the exterior. This internal injury can lead to premature ripening and fruit drop. (Adapted from APAL Integrated Pest Management for Australian Apples & Pears 02/10)

What other methods are available for managing codling moths in orchards?

Cultural, chemical and biological methods can be used to control codling moth.  Strategically applied insecticides are used at the time when larvae are present. There are chemical and biological control options.  The biological options include Bacillus thuringiensis (BT), a naturally occurring bacterium found in soil and plants (sold as Dipel) and the highly specific Grandex insecticide which contains a granulovirus of codling moth.  Mating disruption using pheromone ties in trees may be suitable for large, sheltered orchards.  Natural enemies of codling moth can be encouraged by planting a diversity of flowering species or introducing commercially reared insect species such as Trichogramma wasp and Mastrus wasp. Sterile insect technology complements biological management of codling moth.

What are the benefits of a Sterile Insect Release program

The program can reduce both codling moth damage and codling moth pesticide use in apple production.  The Canadian program has been running since 1991, and they have achieved a 96% reduction in the amount of pesticide used.

Do codling moth attack fruit other than apples?

Yes.  Codling moth infest pears, crab apples, quinces, summer fruit, walnuts and chestnuts

Do sterile moths need to be released every year?

Yes, annual releases will aid in preventing any wild moths from building their population back up to damaging numbers.

How long does it take to get area wide control of codling moth using sterile moths?

In New Zealand, wild codling moth populations in release orchards were reduced by over 90% within a few years of using sterile codling moths.  The population reduced progressively until a very low level was achieved.  This level is lower than the threshold level set for pesticide application meaning growers no longer need to apply pesticides to control codling moth, even for export markets that require pest free shipments. The program works best if the initial levels of codling moth are not high.

Do you have a question?

If you have a question about the sterile codling moth release program that wasn't answered here, please contact Tasmanian Institute of Agriculture.  We would love to hear from you.