For beekeepers with good eyesight, sticky boards can be used to assess the level of Varroa mites in colonies. For beekeepers with poor(er) eyesight or wanting more accurate readings, sticky boards are used alongside other methods like the sugar shake tests or alcohol washes. Once infestation levels are determined, beekeepers can then make a choice on which Varroa management method is required
How Sticky Boards Determine Mite Levels
A “stratified sampling” method is used to estimate Varroa populations within a hive. This procedure involves categorizing bees into separate groups (“strata”) and then counting the number of mites in each group.
What is Stratified Sampling?
Stratified sampling is a statistics method used to obtain more precise data on the honey bee population (Kretzschmar et al., 2015). In the context of the bottom board, it works by dividing the area into separate subgroups, like in the example above, and then counting the population from each one.
Putting this into practice in the field:
- Divide the bottom board area into equal strata. In a Langstroth hive this would be sectioning based on the hive area: front left, front right, back left, and back right.
- The marked stick board reflecting the four quadrants is placed inside the hive for 24-48 hours to collect mites.
- After the collection period, the board is removed and the mites are counted in each stratum, added up and averaged (let’s say you got a total of 12 mites. Divide this by the 4 quadrants, you have a total of 3 mites per quadrants).
- Compare the mite counts in each quadrant – are there areas with higher a mite count than others? What does this look like inside the hive – is that section full of drone brood that can be removed, frozen and replaced to lower mite populations?
To measure improvements, repeat the sampling method over set time frames – whether yearly, or a series of months after treatment (month 1, 3, 5 etc…).
The Anatomy of a Sticky Board
The base material is usually cardboard or wood, with plastic varieties available. The material needs to be strong enough to supports its own weight and that of the falling debris. It’s measured to fit the Langstroth hive dimensions, approximately 56 x 30cm for eight-frame and 55 x 37 cm for ten-frame hives (for a 5-frame nuc, it would be around 55 x 18 cm). Some boards come pre-coated with an adhesive substance, whereas most varieties are a clean slate requiring an adhesive like Vaseline.
Some varieties will be pre-sectioned into grids or contain handles on one end for easier management. If you’re starting with a blank slate, more power to you- divide it how you wish. The board my state department used contained 2.5 by 2.5 cm grids (1 by 1 inches), which they took to a lab to determine the mite density per grid.
Choosing the Right Sticky Board
Consider your current hive bottom boards: are they solid or meshed? The latter is easier to handle – simply insert the board into the (pre-existing) slot beneath the screen or atop the bottom board tray (if it fits). Solid boards require opening the hive and placing it directly underneath on the base through the brood chamber. No, you can’t slide it in through the entrance… unless its opening is wide enough for the entire board.
Keep the board is level and secure (no tears or defects that may skew sampling). In hives with solid bottom boards, a short-term duration of the sticky boards (say, 24 hours) is key, as it to prevents bees from cleaning off the surface and removing the mites. After all, the bees see junk in their colony for removal. The ideal option will allow easy insertion and removal from hives while providing accurate mite counts with little effort to maintain and reuse.
Setting Up Your Board
Start by centering on the bottom board of the beehive so that its entrance aligns with the corners. If the board sits loosely, secure it in place using clips or tape. Ensure to label the board according to which hive it came from (trust me… you’ll forget). Keep boards inside for 24-48 hours and remove for inspection. When such errors can be avoided, you’ll have more reliable data on the hive infestation levels.
Assessing Mite Levels
Mites have a life cycle that sees numbers peak in summer, which are usually twice as high as what’s seen mid-spring. The seasonal life cycle phase can be seen as follows:
- Dormant (occurs only if there is a broodless period – typically Winter or dearth)
- Population Increase (typically Spring)
- Population Peak (typically Summer)
- Population Decrease (typically Autumn)
Where Varroa has been established in regions for years, they exhibit seasonal trends. Varroa populations closely related to honey bee populations, with mite populations reaching their highest levels soon after that of the bees. As the bees and brood decline, so do the mite numbers. When calculating the mite count, keep the season in mind – is this spring? Then the count is likely to increase. Is this autumn? Then the population is likely to decrease.
Regions with temperate climates, like Australia, will not have a dormancy periods, so mites will be present year round, and have a stronger impact on bee health. As such, seasonal variations will drive the type and intensity of treatments – the current chemicals on the market also have seasonal (i.e. temperature) requirements before being deployed in the hive.
The Impact of Brood Interruption
I briefly mentioned removing drone brood in sticky board quadrants with a high mite count. The practice of brood interruption is an integrated pest management strategy that involves the temporary removal of honeybee larvae from within their hive. This disrupts the reproduction process of Varroa, who are mostly found in the drone brood. The costs to the colony is minimal1 – drone brood is dispensable after all. However, a large demand is placed on the beekeeper to coordinate this process, as well as having space to freeze the brood frames.
Complementary Methods to Sticky Boards
Adapted from “How to check for Varroa“
Sticky boards alone give some estimate of mite infestations, however when used alongside other tests, they provide a better estimation of the Varroa populations. Two common tests are the sugar shake and alcohol wash.
The Sugar Shake Test
The sugar shake test is an effective and non-lethal method for assessing the mite population of a bee hive. To perform, powdered sugar is agitated in a screened jar containg bees. Afterwards, the jar is shaken onto a white paper or bowl of water to dislodge mites, and those that fallen are counted. The pros of a sugar shake are that it is quick, simple and nonlethal.
The Role of Alcohol Wash
Around half a cup of bees are collected in a jar and washed with methylated spirits or 70% ethanol, which dislodges any mites from their bodies. The jar is then inverted over a white surface (or water bowl if you wish), emptied and counted. This method is considered to be very reliable but is lethal to bees, so pick your poison.
Screened Bottom Board, Sticky Board & Varroa Mites
Beekeepers use sticky boards in conjunction with other monitoring techniques to assess Varroa mite levels and decide when to treat colonies. If a board is used alone, be sure it sits on the bottom board correctly and is made of solid material. Use stratified sampling procedures to gauge the mite drop on a bottom board. In the field, a combination of testing methods are used accurately assess the number of mites in a hive.
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Footnotes
- Research from Meikle and colleagues (2023) found that the cold storage engagement had a greater impact on bee population than mites over the long term. They suggest this method may be more beneficial in colonies were population are low to begin with… ↩︎
G’day team,
When using a sticky mat in a solid base,
An assumption is made that a metal mesh is placed on top of the sticky mat. What aperture do you think should the mesh have?
Thanks and regards
Hi Moe,
No metal mesh required for sticky mat usage in a solid base hive, apologies if the writing is unclear. If you really wanted to place a mesh atop the sticky board, I would go for something between 2.5mm-4-5mm apertures (is “perforations” applicable here?), as the average Varroa mite is ~ 1.5mm-2mm in length- the idea is to have the holes large enough for the mites to fall through, but not so large that a bee or beetle would get trapped in. Something like a large-diameter flyscreen would work.
All up, I wouldn’t recommend putting a mesh over a sticky mat anyway, the point of the device is to do a mite check by seeing how many fall down over a time period (say, over 24hrs). I mention 24hrs for solid bottom boards because it’s in-hive. If you keep the mat for a longer duration, the bees will eventually clean it up as they see unclean debris… lose-lose for the solid bottom board boys. If you’re after long-duration mite monitoring, I reckon you’re best off using a meshed board- that way you slide the sticky board inbetween the mesh & bottom board; the bees can’t get to it and any dead mite will fall through (along with dirt, debris and hive discards)
Cheers,
Safaa