Bee Pests and Diseases: Identification and Warning Signs

Welcome to our next lesson. In our previous session, we covered the rewarding process of harvesting honey. Now, we shift our attention from the sweet rewards to one of the greatest responsibilities in beekeeping: maintaining the health of your colony. A beekeeper is a steward, and a core part of that role is protecting your bees from the threats that can weaken or destroy a hive.

This lesson will equip you to identify the most common and serious bee pests and diseases. We will focus on two major adversaries: the Varroa mite, which is the single most significant pest for honey bees worldwide, and American foulbrood (AFB), a devastating and highly contagious bacterial disease. Think of this as learning the fundamental diagnostics for your hive. Much like debugging a complex system, you'll learn to recognize specific symptoms that point to underlying problems, allowing you to assess the health of your colony accurately.

The "Most Wanted": An Overview of Hive Threats

While honey bees face numerous challenges, a new beekeeper's efforts are best focused on understanding the most critical threats. The NC State Extension provides a concise overview of the main culprits. We will focus on the top entry in the Adult Parasites list, Varroa mites, and the first entry in the Brood Pathogens list, American foulbrood.

Enemy #1: The Varroa Mite (Varroa destructor)

If there is one antagonist in the story of modern beekeeping, it is the Varroa mite. It is an external parasitic mite, comparable to a tick, that feeds on honey bees and, more critically, their developing young.

The mite itself is a small, flat, reddish-brown oval that is visible to the naked eye. You can get a clear idea of what to look for from the description in this guide from Mississippi State University.

The direct damage from a mite feeding is only part of the problem. The far greater threat is that Varroa mites are incredibly effective vectors for a host of deadly viruses, most notably the Deformed Wing Virus (DWV). A hive can often tolerate the viruses, but when the mites inject them directly into the bees' circulatory system while feeding, the viruses become catastrophic.

This is a relatively new problem. As the video from Michigan State University explains, our Western honey bees (Apis mellifera) have not had enough evolutionary time to develop effective defenses against this pest, which originally parasitized the Eastern honey bee (Apis cerana).

Recognizing a Varroa Problem: Visual Signs

Since you have limited time for your beekeeping activities, learning the most efficient diagnostic signs is key. When you inspect a hive, there are several visual "red flags" that should immediately make you suspect a high Varroa mite level. The following video provides an excellent and practical demonstration of what to look for on the frames.

When these signs become widespread and the colony's population begins to crash, the condition is often called Parasitic Mite Syndrome (PMS). This is the terminal stage of a Varroa infestation, characterized by a spotty brood pattern and sick, discolored larvae. At this point, the hive is often beyond saving.

The Hidden Majority: Why You Must Monitor, Not Just Look

The visual signs you just learned are crucial, but they often only become obvious when the mite population is already dangerously high. The most important concept to grasp about Varroa is that most of the mites in a hive are hidden from view, reproducing under the capped brood.

Because you can't see the majority of the mites, "looking" for them is not enough. You must actively monitor to get a quantitative measure of the infestation level. This is the difference between a casual glance and a proper diagnostic test. The most common methods for beekeepers are the "sugar roll" and the "alcohol wash," which dislodge mites from a sample of bees so they can be counted.

The key takeaway is to calculate your infestation level as "mites per 100 bees." If you take a half-cup sample (about 300 bees) and find 9 mites, your mite level is $9÷3=3$ mites per 100 bees, or a 3% infestation. This number is the critical data point that informs you whether your hive is healthy or requires intervention.

Enemy #2: American Foulbrood (AFB)

While Varroa is a persistent pest you must manage, American Foulbrood is a catastrophic disease. It is caused by a spore-forming bacterium, Paenibacillus larvae, that infects and kills honey bee larvae, typically after their cell has been capped.

The "spore-forming" aspect is what makes it so dangerous. These spores are incredibly resilient, can remain viable for decades, and are resistant to heat and disinfectants. This makes AFB highly contagious and extremely difficult to eradicate. An outbreak is so serious that in many places, it is a notifiable disease, and the only recommended course of action is to euthanize the bees and burn the infected equipment.

Because it is a brood disease, diagnosis involves carefully inspecting the brood frames for a specific set of symptoms.

To summarize the key diagnostic signs of AFB:

• Appearance: Look for sunken, greasy-looking, or perforated cappings on the sealed brood.
• Color and Consistency: Affected larvae beneath the cappings melt down into a brownish, gooey mass.
• The "Ropy Test": This is the classic field test. If you insert a small stick or twig into a diseased cell, stir it, and slowly withdraw it, the larval remains will stretch out into a brown, rope-like thread an inch or more long. This is a hallmark of AFB.
• Odor: The hive may have a distinct, foul odor, sometimes compared to a sweaty gym bag or rotting meat.
• Scale: In the final stage, the larval remains dry into a hard, black scale that is stuck tightly to the bottom wall of the cell and is difficult to remove.

Don't Be Fooled: Differentiating Brood Diseases

Several brood diseases have similar-looking symptoms, but the consequences of misidentifying AFB are severe. The most common confusion is with European Foulbrood (EFB), which is a less serious bacterial disease. The comparative table in the NC State guide is an excellent tool for learning to distinguish them.

Conclusion

Mastering the identification of these two threats is a fundamental step toward becoming a competent and responsible beekeeper. Your ability to spot the signs of disease and pests early is the single most important factor in the long-term survival of your colonies.

Here are the essential takeaways from this lesson:

• Varroa mites are the #1 threat to honey bees. They weaken bees and spread deadly viruses.
• Most mites are hidden under capped brood, so you must monitor with a sugar roll or alcohol wash to measure infestation levels, not just look for them.
• Visual cues like deformed wings, bald brood, and mites on drone pupae are urgent red flags that demand a mite test.
• American Foulbrood (AFB) is a highly contagious and lethal bacterial brood disease, identified by the "ropy test," sunken cappings, and a foul odor.
• Due to its persistence and severity, an AFB infection typically requires the destruction of the hive to prevent its spread.

In our final lesson of this module, we will discuss how to prepare your hive for winter. A healthy, strong colony with a very low mite load is the absolute prerequisite for surviving the cold months, so the knowledge you've gained today is the perfect foundation for that discussion.