Typically, but not always, it is one of two or three things - 1. Varroa Mite issues, or 2. The colony swarmed and failed to re-queen, or 3. Starvation - lack of food or nutritional issues.
1. As you may know, the bees do not die when a mite bites the bee, but the viruses the mites spread when they do bite start to cause enough problems to weaken a colony. When the fast breeding mites increase in numbers that reach the "economic threshold" of around 4 mites per 100 bees, we see problems. Studies have shown having only 2 mites per 100 bees in a colony can cause a drop in honey production, and 4 per 100 can start to cause health issues, so we like to keep the mite numbers to a minimum at all times.
We can check the "mite load" and gauge these numbers using a mite wash. This is done by placing a half of a cup of bees (around 300 worker bees) in a cup of alcohol, or an even better/updated option, a high suds soapy water, like a Dawn dish soap solution, to see how many mites drop off the bees after a minute of standing then another minute of swirling the bees in the liquid above a strainer basket - see link below for a short video of the process.
The number of dead mites in the sample will show your ratio per 100 bees in the colony. Then we treat accordingly. A mite count of less than around 8 to 10 mites per 100 bees can usually be controlled with an extended release treatment, like Oxalic Acid (O/A) / Glycerin strips called VarroxSan or Amatrax infused strips called Apivar. (See Mite Treatments for more) Mite counts in higher ranges will be more effectively treated using a flash treatment, like a O/A dribble or O/A vapor, or even a Thymol or Formic acid treatment. (multiple applications may be required for the O/A options and cooler weather required for the latter two)
2. Sometimes a colony will swarm and the remaining hive is not able to get a new queen produced for one reason or another, so they eventually die off as they age out and no bees are being born to replace the ones that die from old age... or more specifically, work them selves to death.
3. Starvation obviously occurs when the bees run out of food stores and there is not enough coming in on a daily basis to support the number of bees in the colony. A common mistake is assuming the bees have plenty of food available because there are "lots of flowers bloom" or "they are wild animals and can take care of themselves". While it is of course true that bees depend on flowers for their food, the flowers depend on moisture to produce nectar. When we are in a drought, or a dearth, as we often are in Texas, the flowers are not always producing enough food to support the bees - especially year round. So we check the hives and feed as needed.
When any of these things happen and there's little to no bees to defend the nest, the wax moths are free to move in and lay their eggs. When these eggs hatch, the "wax worms" (Wax Moth larvae) become the "clean up crew" for any remaining food left behind.
When we discover wax moth damage, we inspect and evaluate the frames in the hive. Some may not be damaged at all, while other frames may be completely void of any wax/honeycomb. There may be some of each, but all are prone to have eggs that are not visible and can cause future damage if not addressed soon.
We like to salvage any remaining frames with decent wax and clean up the mess from the rest. Placing any good frames with wax in a freezer for about 72 hours will normally kill off any remaining moth eggs and / or larvae and can be reused after they thaw out.
Inspect the frames to determine how much can be saved. The wax is valuable to the bees and can be cleaned by the bees on the frames with minimal damage. If the wax is no longer sturdy and full of webbing and frass (fecal matter and waste), then it is best to clean it for them and save the bees a lot of work.
When the damage is beyond salvaging any wax then it's best to simply clean up the webbing mess and cocoons so the frames can be reused. Scrape off the unusable parts, meaning the really badly damaged honeycomb that is no longer structurally sound and any small cocoons on the wooden parts.
Adding a coating of fresh wax will be helpful, otherwise the bees may not build out wax on the foundation after the infestation has occurred.
Keeping strong hives is the best prevention to most issues in the bee hives.
Randy Olivar's Mite Wash Video:
https://youtu.be/oiu_dIZu7Uk?si=tQHYDeLaFlRENHZj
