The Small Hive Beetle (SHB), Aethina tumida, is an invasive pest that poses a significant threat to honey bee colonies, particularly in warm, humid climates. Originating in sub-Saharan Africa, the beetle acts as a scavenger and parasite in European honey bee colonies. Adult beetles reproduce rapidly, and their larvae quickly overwhelm weakened hives by damaging comb and spoiling stored food. Determining a fixed number for “too many” adult beetles is unreliable because the threshold for a damaging infestation depends highly on the colony’s condition.
Indicators of Infestation Beyond Just Counting
The true indication of a severe beetle problem comes from observing the destructive effects of the larval stage, not just the presence of adult beetles. The larvae are small, white, grub-like creatures with three pairs of legs near the head. They tunnel through honey and pollen stores, consuming the contents and leaving behind waste.
This larval activity introduces a yeast, Kodamaea ohmeri, which causes the stored honey to ferment and bubble. This fermentation results in a characteristic rotting or “decaying orange” odor emanating from the hive. The damaged honey then leaks out of the cells, creating a wet, greasy mess known as “sliming,” which signals an uncontrolled infestation. Finding these larvae, fermenting honey, or the foul smell signals a more immediate problem than simply seeing a few adult beetles.
The Contextual Nature of the Infestation Threshold
There is no established fixed number or “economic threshold” of adult Small Hive Beetles that automatically signals colony collapse. The threshold is instead based on a “beetle-to-bee ratio,” which assesses the colony’s capacity to manage the pest population. A robust, populous colony can often contain dozens of adult beetles by corralling them into small, propolis-lined crevices where they cannot lay eggs. The colony’s defensive capacity is the most significant factor in preventing an infestation from becoming destructive.
A strong hive with a high bee population can easily tolerate 25 to 50 adult beetles, as the bees actively patrol and remove any eggs or newly hatched larvae. Conversely, a weak nucleus colony or a hive stressed by disease or poor weather may be quickly overwhelmed by as few as 5 to 10 adult beetles. These lower bee numbers mean fewer workers are available to guard the comb, allowing the beetles to lay eggs and reproduce successfully.
The hive’s size also influences the threshold, as a single-box nucleus colony has less territory for the bees to patrol compared to a double-brood box colony. Environmental factors, such as high heat and humidity, also reduce the threshold for damage because these conditions accelerate the beetles’ life cycle, increasing their reproductive rate. The peak danger often occurs in late summer when beetle populations are high and colony populations may naturally begin to decline.
Practical Methods for Assessing Beetle Population
Beekeepers use several practical methods to estimate the adult beetle population and assess the risk level within the hive. A quick visual inspection involves observing the inner cover and the top edges of the frames, as adult beetles avoid light and run to dark, protected areas upon disturbance. Beekeepers may also observe the bottom board, where beetles often migrate downward during inspection.
More accurate assessment relies on passive trapping devices placed inside the hive. The most common is a sticky board or a screen bottom board trap placed underneath the brood chamber. Another effective tool is a corrugated plastic diagnostic strip, which is inserted through the hive entrance and allows beetles to hide in the flutes; it can capture about 30% of the total adult population.
In-hive traps, such as those that use mineral oil or diatomaceous earth to drown or desiccate the beetles, are used for both monitoring and control. These traps are designed with openings that allow the smaller beetles access while excluding the larger honey bees. Regular monitoring provides a consistent, measurable count that allows the beekeeper to track population trends and determine when the colony’s defensive capacity is exceeded.
Strategic Intervention Following a High Count
When monitoring indicates the beetle population has surpassed the colony’s ability to manage it, immediate intervention is necessary to prevent collapse. The first step involves cultural controls aimed at strengthening the colony and reducing the beetles’ access to resources. This includes consolidating a weak colony by removing excess supers and ensuring the bees cover all available comb, which reduces unprotected space where beetles can lay eggs.
Physical removal is another immediate action, involving crushing visible adults and deploying specialized in-hive traps that remain long-term. These traps use a reservoir of oil or a non-toxic powder like diatomaceous earth to kill beetles attempting to hide inside. If a severe infestation involves many larvae, contaminated frames must be quickly removed and frozen to kill all life stages, preventing larvae from exiting the hive to pupate in the soil.
For persistent problems, a multi-pronged approach may include chemical controls, such as applying an approved soil drench like permethrin around the hive to kill pupating larvae. Internal chemical strips may also be used in some regions, but beekeepers must strictly follow all local regulations and application instructions to ensure the safety of the bees and hive products. The goal of intervention is to disrupt the beetle’s life cycle and restore the beetle-to-bee ratio in favor of the honey bee colony.