Understanding and managing the role of honey bees in CGMMV epidemiology (HortInnovation VM18008)
Cucumber green mottle mosaic virus (CGMMV) is a plant virus that affects cucurbit crops including watermelon, cucumber, melons, zucchini and pumpkin. This virus is highly destructive and contagious and can lead to significant reductions in productivity and fruit quality. The virus was first detected in Australia in 2014, and is now found in many states and territories. CGMMV is most likely introduced into a crop through infected planting material (soil, seed or seedlings) and can be mechanically transmitted (by something as small as using secateurs to prune plants, or something as large as driving a tractor through a crop).
Cucurbit crops are almost 100% pollinator dependent, they require insect pollination for successful fruit set and production. In Australia, honey bees are regularly used to provide managed pollination services to broad acre watermelon cropping. Based on previous research conducted in Australia and elsewhere, we know that honey bees are able to move CGMMV from one flower to another and that the virus can persist in bee hives. CGMMV is not known to affect bee health. However, the main concern is that if honey bees are exposed to CGMMV and then moved significant distances within or between states, they may be move this highly destructive plant virus to new locations.
Honey bees and their role in CGMMV spread
The project’s results indicate that honey bees can spread CGMMV when pollinating infected and healthy crops at the same time. However, the intensity of this transmission is dependent on the availability of the infected plants at the property. The risk (likelihood and proportion) of virus transmission increases the greater number of CGMMV-infected plants at the property.
The evidence from this project is that the risk of foraging honey bees introducing CGMMV into new areas when their hives are moved is low. The project team’s field transmission trials showed that the window for transmission of CGMMV by foraging bees from a hive that has been recently exposed to CGMMV positive plants is less than 24 hours. Resting site hive trials showed that CGMMV was no longer detectable on honey bee bodies after one month. Therefore, it is recommended at least one month resting of CGMMV positive bee hives at a CGMMV free location to stop virus transmission of CGMMV by honey bees from positive hives.
Also, avoid bee hive management practices – such as hive splitting and honey extraction – while hives are present at a site of cucurbit production. This is because it could be possible to physically infect living cucurbits with viable CGMMV still contained in bee hive materials (such as wax frames or honey) when they are removed from the hive.
Therefore, the recommended management strategies to reduce CGMMV transmission via foraging bees and positive bee hives are:
- Proper and early removal of infected plant material from the property.
- At least one month break for hives that have had a known or presumed exposure to CGMMV positive plants before introducing them to another cucurbit crop.
- Avoid conducting hive management practices for suspected CGMMV positive hives on cucurbit producing properties.
Honey bees that have been exposed to CGMMV are not the most significant source of CGMMV. It is a plant virus that is most frequently introduced in seed/infected planting material and can be moved in soil, plant material or on contaminated equipment.
The project has produced fact sheets for melon growers and apiarists for specific management practices to avoid CGMMV transmission via bees and positive bee hives. Please visit Hort Innovation website for the final project report and factsheets.
This project has been funded by Hort Innovation using the melon research and development levy and contributions from the Australian Government.
Project Number: VM18008