Anne Dollin, Chair of the ANBA Varroa Response Subcommittee
Native bees in eastern NSW continue to face a severe threat, following the discovery of varroa mites, a devastating pest of European honeybees, in Newcastle eleven months ago.
An urgent eradication program was set up by NSW De-partment of Primary Industries (DPI) and widespread baiting is now underway using Fipronil, a pesticide that is highly toxic to bees.1, 2
The current size of the varroa mite incursion
The DPI declared a Red Zone around each location where varroa mites were found in their inspections of European honeybee hives. The two maps show how the Red Zone areas have expanded since 27 December 2022.
Since my last Cross Pollinator update in January, over 40 more Infested Premises have been found, and varroa mites have now been recorded in 156 Infested Premises.3
In April 2023, the DPI estimated that varroa mites had spread through 9,450 square kilometres of NSW.4
The DPI eradication plan
Despite the large size of this varroa mite incursion, the DPI believes eradication is possible. They aim to eradicate varroa mites from this incursion by 30 June 2026.4
Any European honeybee could spread this mite further. So the DPI aims to destroy every European honeybee colony within the Red Zones, whether they are in a man-aged hive or a feral nest.
So far, over 22,000 managed European honeybee hives have been euthanised in the Red Zones.4 Sadly, this has had a deep impact on many beekeepers in the affected areas.
However, the eradication of the feral nests of European honeybees in the Red Zones presents a different kind of challenge. Conservatively, there would be thousands or tens of thousands of feral European honeybee nests within the current 9,450 sq km Red Zone area.
Most of these feral nests cannot be simply destroyed by a pest controller because they are in inaccessible or unknown locations. So to destroy these nests, the DPI is using sugar syrup bait stations that are spiked for short periods with Fipronil pesticide. Over 600 stations are currently in use in the Red Zones.4
Fipronil baiting began in October 2022 and will continue at least throughout 2023. Each area is given two 30-day cycles of baiting work within a period of 90 days. Further baiting cycles may be done if this regime does not achieve full honeybee eradication in an area.5 Some are-as in northern Newcastle have still not commenced their first cycle. A chart showing when Fipronil pesticide will be used in each Red Zone area can be found HERE.
Expansion of the DPI Red Zone areas, where varroa mites have been found, in the five months from 27 December 2022 to 21 May 2023. The number of Infested Premises increased from 109 to 156 during this period. The yellow lines have been added to aid comparisons of the two maps. There are two other Red Zones, at Narrabri and at Nana Glen near Coffs Harbour, which are not shown.
Potential impact on native bees
The DPI is striving to prevent non-target species, such as threatened species and native bees, from accessing the Fipronil pesticide. Their strategies include modifying the bait station design, and selecting locations away from endangered species habitat.4
However, the baiting program will produce thousands of dead feral European honeybee nests within the Red Zones. Each dead nest will hold a large reserve of honey which may be contaminated with Fipronil. Non-target species, including native bees, could be poisoned by col-lecting honey from these dead feral honeybee nests. Contrary to a view presented by Nathan Cutter, DPI,4 in my experience native stingless bees are strongly attract-ed to undefended honey resources and could actively recruit other foragers to a dead feral honeybee nest.
A study in New Zealand investigated methods of destroying feral European honeybee colonies to control pests of bees. They found that Fipronil which is diluted in honey remained toxic enough to kill honeybees for at least 26 months, when stored at 25o C.6 So the risk to native bees and other non-target species from the DPI program could persist for a long time.
Fortunately, the risk to native bees from the Fipronil baiting is currently low, because most native bee species in NSW are either dormant or fairly inactive at present, due to the cold weather. However, once the warmer weather returns in spring, the risk to native bee populations will again increase.
ANBA advice to stingless bee keepers
The ANBA advice to affected native stingless bee keepers still stands: they should consider moving their hives out of the Red Zones for up to three years. An ANBA offer to assist beekeepers with this process, if needed, is also still available. For full details, see: https://www.anba.org.au/varroa-response/
- A detailed webinar by the DPI on their varroa response, 11 May 2023: https://www.youtube.com/watch?v=8eh1ddThvys
- Australian Honey Bee Industry Council and DPI briefing, 31 August 2022: https://www.youtube.com/watch?v=f3oV0O0JqVM
- Taylor MA et. al. (2007) Destroying managed and feral honey bee (Apis mellifera) colonies to eradicate honey bee pests, New Zealand Journal of Crop and Horticultur-al Science, 35:3, 313-323, https://www.tandfonline.com/doi/abs/10.1080/01140670709510197