What was it all about?

This investment, which ran from 2019 to 2021, determined the mechanisms by which honey bees introduce cucumber green mottle mosaic virus (CGMMV) into healthy cucurbit plants and developed recommendations to manage the transmission of CGMMV by honey bees.

Exposure to CGMMV is a significant concern for growers and also for the bee industry, with the virus being highly destructive and contagious. It was first detected in Australia in the Northern Territory in 2014 and has now been detected in the majority of states and territories.

The research team used lab and field trials to investigate CGMMV transmission by pollinating honey bees. They demonstrated that when CGMMV is already present in a crop, honey bees visiting flowers within the crop can transmitted CGMMV between infected and healthy plants. This does not represent a significantly greater risk than any other mechanical transfer of the virus.

The research demonstrated that if honey bees visit the flowers of CGMMV positive plants and their hive is then moved to a new location, bees foraging at the new location are able to cause CGMMV infection in cucurbit plants. This is the first time this transmission pathway has been confirmed.

CGMMV accumulates in honey bee hives when bees collect nectar and pollen from CGMMV positive plants. Standard hive management practices (spinning off honey, changing frames) reduced the detectability of CGMMV inside bee hives. CGMMV on bees from within the hive was detectable up to one month after the hive had been exposed to CGMMV positive plants. CGMMV was detectable in honey from within the same hives for over 12 months, but the virus was not viable.

Pollen samples from honey bee hives were analysed, and although 151 plant species were identified, the project team were unable to infer the plant source of the CGMMV detected.

ACT NOW

The project produced a number of fact sheets, available below:

• Pollinating honey bees: are they plant disease vectors?
• The role of honey bees in CGMMV epidemiology
• CGMMV and honey bees

A recording of a webinar presented on the project's findings can also be viewed here.

Recommendations for growers:

• Proactively manage biosecurity practices on your farm.
• Discuss the CGMMV status of your crop with your apiarist.
• Discuss the CGMMV status of any bee hives that you bring onto your property.
• Ensure hives used on your property have not been exposed to CGMMV within the past month.
• Ensure that hive materials (wax frames, honey) are not discarded in your cucurbit production areas.

Recommendations for apiarists:

• Manage your apiary’s exposure to CGMMV by knowing the status of the cucurbit crops you service
• If a hive has been exposed to CGMMV within the past two weeks the bees may be able to transfer CGMMV to other cucurbit plants when visiting flowers.
• Keep concise and accurate records on hives and loads, to enable trace back to determine the source of the disease.
• Physically separate loads based on the sites they have worked.
• Remove CGMMV positive material from hives store equipment and consumables on the apiary in such a fashion that bees cannot access it.
• Honey supers should be separated at the extraction plant and not interchangeable between loads.
• Hive equipment should be cleaned between loads to ensure all wax and honey debris is removed.