Understanding and managing the role of honey bees in CGMMV epidemiology (VM18008)
What’s it all about?
Beginning in July 2019, this project is exploring how honey bees are able to introduce cucumber green mottle mosaic virus (CGMMV) into melon crops, and is developing management practices to combat this for both the melon and apiary industries.
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 project’s work will build on earlier research in the Hort Innovation Vegetable Fund, and deliver updated fact sheets and management plans.
Laboratory and field trials demonstrated that when CGMMV is already present in a crop, honey bees travelling from flowers on CGMMV positive plants to flowers on clean plants cause infection in the clean plant. Further investigation will be undertaken in the coming season on whether bees from hives that contain CGMMV are able to transmit the virus to clean plants.
The team also monitored the persistence of CGMMV in honey bee hives, conducing controlled trials to mimic resting (as part of standard hive management) and in-hive conditions. In the hive management / resting trial, samples were taken at set intervals over 14 months, with results showing a significant reduction in CGMMV detectability (only found in capped honey). In the trial to assess in-hive conditions, samples were taken monthly, with CGMMV still readily detectable after 14 months. Viability studies to test whether the CGMMV present can cause infection are underway.
The team also commenced a newly defined literature review to:
- review plant pathogens known to be transmitted by honey bees
- assess the survival of these pathogens in bees and bee hives, based on available information
- outline mechanisms of transmission, both known and hypothetical
- specifically review high or medium risk pathogens of cucurbits from current industry biosecurity plans and assess the likelihood of their transmission by honey bees.
The project team maintained regular communication with stakeholders and industry partners. Project updates were provided to the melon and apiary industries, along with site visits to properties and apiaries in the Northern Territory.
The project team continue activities to determine how honeybees introduce Cucumber green mottle mosaic virus (CGMMV) into healthy melon plants and develop management practices to combat this disease.
Since the last project update, seven apiaries in the Northern Territory (Katherine, Mataranka and Darwin) were tested for the presence of CGMMV, with five apiaries in Katherine testing positive, but the apiaries in Mataranka and Darwin showing as negative.
A pilot study to test the viability of infected hive samples (i.e. adult bees, pollen and honey) from one of the Katherine apiaries was conducted. After three months of removing all honey and pollen from the hive, the virus was still detected in almost all samples of adult bees, broods, new honey and pollen.
Experiments to test how long CGMMV remains in infected honey continue. Honeycombs from six CGMMV positive hives, under temperature-controlled conditions, are being sampled monthly over a 12-month period. The samples will then be tested for CGMMV presence and viability.
Field trials to determine how bees introduce CGMMV into plants have commenced at Berrimah Farm Science Precinct in Darwin. The first trial has commenced, investigating CGMMV transfer by healthy bees from infected plants to healthy plants. An additional experiment observing virus transfer to healthy plants from infected bees/hive is planned.
Adult bees collected from apiaries (two in Katherine and one in Mataranka) were tested for two other possible mosaic viruses (papaya ringspot virus type W and zucchini yellow mosaic virus) that are present and established in the Northern Territory. Molecular test results confirmed that the samples are negative for the target viruses. More samples will be collected at the end of the 2020 melon growing season.
The team are also conducting a broad literature survey, and continue to engage and share information with industry members.
Read more about project progress in this article, Understanding the role of honey bees in CGMMV, published on page 9 of Melon News, June 2020 edition.
The project team reports progress in the following areas:
- Seven commercial apiaries located in Cucumber green mottle mosaic virus (CGMMV) affected areas have been selected for testing. All apiaries were in Northern Territory (five in Katherine and one each in Mataranka and Darwin) and have been sampled and lab tested (using three molecular assays) for the presence of CGMMV. A study to test the viability of the positive samples is being conducted.
- Experiments to test the longevity of CGMMV in infected honey have commenced through assessing six infected honeycombs over twelve months with regular viability assessments at six, nine and twelve months.
- Monitoring of infected hives after honey and pollen harvesting was conducted through molecular testing which found positive detection of CGMMV after three months.
- As discussed at the project start-up meeting, field trial 1 was moved to early 2020 (rather than October 2019) and reporting on this trial will be detailed later. Preparation for this first field experiment to determine the possibility of CGMMV transfer by honeybees to healthy plants has started and bee training for the experimental plants is being conducted.
- Initial bee samples from Katherine and Mataranka were tested for other potyviruses (papaya ringspot virus type W and zucchini yellow mosaic virus) which are prevalent in the area and found all samples were negative. This testing will be repeated at the end of the year for further monitoring.
- Testing for the pollen samples from other possible hosts has been arranged with AgriBio, Centre for AgriBioscience, DPJR, Victoria.
- The 2020 Syngenta Australian Melon Conference and Field Day has been cancelled due to the COVID-19 restrictions, however alternative delivery methods are being explored to provide industry with research updates and presentations which would have occurred at the event.
This project is a strategic levy investment in the Hort Innovation Melon Fund