Screen-bottomed hives deter varroa mites but not productivity

A New South Wales Department of Primary Industries (NSW DPI) study has revealed using screened base boards instead of the usual solid ones on honey-bee hives has no negative impact on hive productivity, and some significant positives – such as deterrence of pests and parasites, including the destructive varroa mite.

Varroa mite on bee pupae: the new hive base screens act to deter these destructive parasitic mites.
Varroa mite on bee pupae: the new hive base screens act to deter these destructive parasitic mites.
CSIRO

The research, conducted under the DPI’s Honey Bee and Pollination R&D Program and released in December 2014, is part of a collaborative effort to prepare our agriculture industry for a likely varroa mite incursion. The blood-sucking parasite has devastated bee populations globally and will likely have a similarly damaging effect Australia’s honey bee population, if and when it arrives, with flow-on effects to pollination services and honey production.

If beekeepers are to ensure that the world’s sole remaining varroa-mite-free zone is prepared for these damaging insect pests, it’s crucial they adapt to best practice, contends project spokesperson James Kershaw. “And the research shows screened bottom boards can provide substantial gains in preparation for the mite’s arrival.”

Dr Denis Anderson of CSIRO's Entomology division examines a hive at a cherry farm near Young, NSW.
Dr Denis Anderson of CSIRO's Entomology division examines a hive at a cherry farm near Young, NSW.
Nick Pitsas, CSIRO

It has been established that screened bottom boards on hives act as effective, though not impenetrable shields against varroa mites but many beekeepers are dubious about using this method to manage incursions. Their concern is that though the screens might deter varroa mites, they could expose the bees inside to greater variations in hive temperature as well as drafts, negatively affecting productivity.

To test this possibility, the DPI project team, headed by the department’s Dr Doug Somerville, compared screened and unscreened (solid bottom-board) options on hives in various locations and under different seasonal conditions.

The results revealed no significant difference in the productivity of bee colonies in hives with screened as opposed to solid base boards. “In fact,” Kershaw says, “the screened bottom boards provide many advantages for beekeepers, not just in the management of varroa.”

The three-millimetre holed wire mesh typically used in screened bottom boards, often in conjunction with sticky mats, stop the parasitic mites from re-entering a hive once they have been dislodged and have fallen through the screen onto the ground.

Mesh screens affixed to the bottom of hives deter varroa mites and other unwanted pests.
NSW Department of Primary Industries

“One of the main benefits right now for Australian beekeepers is the lack of build-up of debris on the floor of the hive with a screened bottom board. Excessive debris is an ideal haven for wax moth larvae and small hive beetles, which are major pests of bee hives,” Kershaw explains.

The DPI study found that the productivity of bee colonies in screen-bottomed hives did not decrease with chillier winter weather; indeed, the additional ventilation the screens provided was a positive as it tended to reduce hive humidity and mould.

Bottom screens also mean an apiarist can lock a colony into a hive using an entrance shutter – which, “in an emergency, allows for hive repositioning during the day, limits honey bee exposure to harmful chemicals and reduces the risk of the colony overheating in the hot Australian climate”, Kershaw says.

“The use of screened bottom boards alone will not control varroa mites but they can be a significant benefit in their management.”

The Honey Bee and Pollination RD&E Program is a partnership jointly funded by the Rural Industries Research and Development Corporation (RIRDC), Horticulture Innovation Australia Limited (HIA Ltd) and the Australian Government Department of Agriculture

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