How Do Screened Bottom Boards Reduce Varroa Mite Populations? Enhance Your Hive's Integrated Pest Management

Screened Bottom Boards (SBBs) function as a passive mechanical barrier that permanently removes Varroa mites from the colony. By replacing the traditional solid wooden hive floor with a mesh of specific dimensions (metal or plastic), SBBs ensure that any mite dislodged from a bee falls through the screen and out of the hive, preventing re-attachment.

Core Takeaway Screened Bottom Boards are a foundational tool for Integrated Pest Management, providing a continuous, chemical-free reduction in mite populations ranging from 13% to 21%. While they significantly lower the mite load, they are a partial measure and should not be relied upon as the sole method of Varroa eradication.

How the Mechanism Works

Exploiting Natural Grooming

Honeybees possess natural grooming instincts and will attempt to remove parasites. Additionally, mites frequently fall off bees accidentally during normal hive activity.

The Problem with Solid Floors

In a hive with a traditional solid wooden bottom board, a fallen mite lands on the floor. Because the mite is still inside the hive, it can easily crawl back onto a passing bee and re-enter the colony's population.

The Solution: A One-Way Exit

Screened Bottom Boards interrupt this cycle. When a mite falls—whether through grooming or accident—it drops through the mesh. Once the mite passes through the screen, it is physically unable to climb back up to the bees, resulting in its permanent removal from the colony.

Realistic Expectations for Efficacy

The 13% to 21% Reduction

Primary data indicates that the use of Screened Bottom Boards results in a natural mite population reduction of approximately 13% to 21%.

Continuous Passive Control

Unlike chemical treatments which are applied episodically, SBBs work 24 hours a day, year-round. This provides a baseline level of protection that slows the overall growth rate of the mite population.

The Dual Benefit: Monitoring and Assessment

Non-Destructive Sampling

Beyond reduction, SBBs are critical for quantification. By sliding a "sticky board" (a stiff sheet coated with adhesive or glycerol) underneath the mesh, beekeepers can catch falling mites.

Objective Data Collection

The mesh prevents the bees from reaching the sticky board to clean it. This allows the beekeeper to count the fallen mites accurately to determine natural mortality rates.

Calculating the Drop

For a reliable assessment, the sticky board is typically left in place for three days. Dividing the total mite count by three provides the average daily mite drop, a key metric for deciding when to intervene with stronger treatments.

Limitations to Consider

Not a Silver Bullet

A 21% reduction is significant, but it leaves the majority of the mite population intact. SBBs suppress the population curve but do not eliminate the infestation.

Differentiation from Robbing Screens

It is important to distinguish SBBs from robbing screens. While SBBs handle mites already inside the hive, robbing screens are installed at the entrance to prevent foreign foragers from bringing new mites in. SBBs do not prevent the entry of mites via drifting or robbing bees.

Making the Right Choice for Your Apiary

To get the most out of Screened Bottom Boards, align their use with your specific management goals:

If your primary focus is Pest Management (IPM): Install SBBs permanently to gain a "free" 13-21% reduction in mite load, reducing the pressure on your chemical treatments.
If your primary focus is Monitoring: Utilize the SBB with a sticky board or glycerol sheet for 3-day intervals to accurately track infestation levels without opening the hive.
If your primary focus is Total Control: Do not rely on SBBs alone; pair them with appropriate chemical or organic treatments to address the remaining mite population.

Used correctly, Screened Bottom Boards are an essential, non-invasive foundation for a healthy, low-chemical apiary.

Summary Table:

Feature	Description	Impact on Mite Control
Mechanism	Passive mesh barrier (metal/plastic)	Prevents dislodged mites from re-entering the colony
Efficacy Rate	13% to 21% population reduction	Slows infestation growth without chemical use
Monitoring	Compatible with sticky boards	Provides accurate daily mite drop data for assessment
Operation	24/7 continuous passive control	Reduces dependency on episodic chemical treatments
Versatility	Foundation of IPM strategy	Works year-round to lower overall colony stress

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References

Jernej Bubnič, Maja Ivana Smodiš Škerl. Three pillars of Varroa control. DOI: 10.1007/s13592-021-00903-4

This article is also based on technical information from HonestBee Knowledge Base .

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How do Screened Bottom Boards reduce Varroa mite populations? Enhance Your Hive's Integrated Pest Management