Researchers at the University of Sydney have refined a technique for rapidly assessing the number of honey bee colonies in an area.
“Due to the current COVID-19 pandemic we have never been more aware of how diseases move through a population,” said Michael Holmes, one of the project’s researchers.
“We have seen that outbreaks are much harder to contain in areas with dense populations and the same principle would apply if varroa were to make it to our shores.”
“With our density assessment technique, surveys can now be done around the country to work out which areas are more densely populated with honey bees.”
“If an area is densely populated, we know that this will be an area to focus containment efforts on during an incursion.”
Michael explained that the technique which is called ‘bee ballooning’ exploits the unique mating behaviour of honey bees.
A conical net suspended from a weather balloon is launched into the air at a drone congregation area, a clear grassed area where male honey bees (drones) and virgin queens gather to mate.
The net contains lures that have been soaked in queen pheromone, making them irresistible to drones, who enter the net and are trapped.
The trapped drones are then returned to the lab for genetic analysis.
“We use genetic markers to determine how many of the drones in the trap were produced by the same queen,” said Michael.
“If we catch 1000 drones and find that they are produced by 150 queens, then we know there are at least 150 colonies within flight distance.”
Bee ballooning was successfully used to determine whether Asian honey bee colonies were present during the 2016 Varroa jacobsoni incursion in Townsville, Queensland.
Since then the researchers have learnt how to use the technique to work out how densely colonies are packed in the environment, as well as how many colonies are present.
Michael explained that they found a new statistic that was previously unknown – the distance drones fly when searching for a mate.
“We artificially stimulated a colony to produce drones during the winter and paint-marked thousands of them,” he said.
“Then we launched a balloon trap at 250 metre intervals in opposite directions: every time we caught a marked drone we moved to the next interval.”
“We caught drones at every interval up to 3.75km from the colony.”
“At 4km, we caught no marked drones, and genetic analysis revealed that the unmarked ones caught at this distance were not from our focal colony.”
From this experiment, the researchers determined that drones fly up to 3.75km when searching for a queen to mate with, but not as far as 4km.
With this information, bee ballooning can now be used to measure how densely packed colonies are in an area, since any drones caught will have come from colonies within a 3.75 km radius of the trap.
The work described in this article part of the Rural R&D for Profit Program Securing Pollination for More Productive Agriculture funded by Agrifutures Australia.
Utaipanon, P., Holmes, M. J., Chapman, N. C. and Oldroyd, B. P. (2019) ‘Estimating the density of honey bee (Apis mellifera) colonies using trapped drones: area sampled and drone mating flight distance’, Apidologie, 50(4), 578–592.