Papua New Guinean beekeepers have suffered from the same species of varroa 10 years longer than Fijians, so we can learn from the PNG experience.
Anecdotal evidence from PNG suggests substantial negative impacts on honey production. In the early years, untreated in PNG, it caused bee colony deaths estimated at 60% – 90% in some areas.
One study reported disease consistent with parasitic mite syndrome. However, many bee colonies survived and show some tolerance to the mites.
Integrated pest management (IPM) approach
Most varroa mite experts advise beekeepers to adopt an integrated pest management (IPM) approach to controlling varroa.
An IPM approach uses several methods to reduce the adverse effects of mites.
Here are a few ways:
Method 1 of Controlling Varroa Mites: Mechanical And Cultural (Non-Chemical) Control
Removing drone brood is probably the most practical non-chemical varroa mite control method for Fiji, as it only takes a minute to cut drone brood out of frames in the top box of a hive during regular monthly inspections. It can be effective because varroa reproduces primarily on drone pupae.
Varroa mites show a strong preference for breeding in drone cells because they can raise more babies during the drone’s longer development period.
Carve drone brood out of specially designed frames
Some beekeepers overseas routinely carve drone brood out of specially designed frames for this purpose. It is also a good beekeeping practice to keep newer, good quality worker-sized comb in the bottom hive box, so drone pupae only needs to be removed from the top box.
I made some of these frames and plan to place two into the top box of each hive. The bees will build mostly drone-comb in the open bottom section. 
A shallow frame in a full-depth box allows the bees to build comb on the bottom of the frame. Most of the cells the bees build will be drone-sized. BTW, the light patches on the comb are only caused by sunlight
Causing a ‘break’ in bee brood-rearing
Causing a ‘break’ in bee brood-rearing is another control method, as it denies the mites a place to breed.
The easiest way to do this is to create walk-away splits each year as they are broodless for the first few weeks. Pinching old queens to let colonies raise a new one works in a similar way.
Caging queens for a couple of weeks to stop egg-laying also works, but that would be an enormous amount of labour for someone with many hives.
Hive bottoms with screens
Hive bottoms with screens that allow mites to fall through instead of solid wood is commonly believed to reduce mite loads by approximately 10%, as some mites naturally fall to the bottom and cannot return to the colony.
Unfortunately, the right size mesh (approx 3mm holes) is nearly impossible to find in Fiji. Has anyone found a good substitute?
Photos courtesy of John Caldeira
The screening must be large enough for the mites to fall through, but small enough to keep out robber bees and other pests.
The best screening to use has 3 mm holes, commonly referred to as “number 8 mesh” (8 wires to the inch) but it has been difficult to find this mesh in Fiji.
This same mesh is good for the lids on sugar-shake jars.
Arranging hives in an apiary so that hive entrances are not near each other will minimize the ‘drifting’ of forager bees that mistakenly enter the wrong hive, thus reducing the spread of varroa between hives.
Photos courtesy of John Caldeira.
Originally posted on Fiji Beekeepers Association Facebook Group by John Caldeira: https://www.facebook.com/groups/FijiBeekeepers/