Fat Bodies? Vitellogenin?

Fat bodies are not the same thing as being fatter bees! Fat bodies are physical structures within bees that control and enhance energy storage and production.

Vitellogenin in honey bees serves as both a form of nutrition and as a nutritional stockpile within the individual bee. How do you pronounce vitellogenin?

In July, when the bees are bustling around and seemingly healthy and content, you probably can't imagine this hive dying in six months. Your inspections may look terrific, with full frames of brood and multiple supers filling with nectar and honey. Yet, it is precisely these bountiful conditions that can lead to trouble down the road. Of course, you plan to treat for Varroa destructor mites to protect your winter bees, but it’s not even fall, yet! But it’s not too early to start thinking about your vulnerable winter bees, either.

Why should mite treatment begin early?

Winter bees are different from the summer foragers that leave the hive every day: They’re born under different, scarcer food-availability conditions, which in turn, leads to them having somewhat different physiology, with more internal fat bodies which can store more vitellogenin, a substance which provides essential energy and nutrition to winter bees so that they can live for several months, instead of just the 6 or 7 weeks of warm season bees.

These long-lived bees are what enable a hive to get through the winter with a large enough population to cluster around next year’s first rounds of brood, even in frigid outside weather. There simply must be enough of them to get that job done, or the hive will fail. The increased number of fat bodies in winter bees and the larger amount of vitellogenin created are what do the trick.

What could go wrong with that? Well, of course, the Usual Suspects: varroa mites and the diseases they spread.

How mites and mite-vectored diseases affect winter bees

A hive needs a certain critical mass of winter bees to do the job of keeping the early rounds of brood warm. If there aren’t enough of them when the queen begins laying again, the brood will become chilled and die before the winter population ages out.

Even though winter bees live longer, most will have died long before winter is truly over. These are replaced by the brood that began as eggs laid in deepest winter. Unless, of course, not enough of those eggs successfully reach adulthood: Parasitization of either adults or pupae by varroa mites shortens the bees’ lives and disrupts the critical timing of this winter-to-spring “just-in-time” bee-replacement cycle.

How do varroa mites affect bees?

When varroa mites bite bees, they are looking for food. One of their preferred targets are the fat bodies that sustain and protect wintering bees. This is why you don’t want to go into winter with heavy mite loads.

Varroa mites both feed and reproduce on capped, pupating, bee brood. And in the early part of summer, bees have the highest amount of capped brood of the whole year. As much as 80% of the total number of varroa mites in a hive in July may be tucked in with the developing pupae. A queen at her full summer laying pace may fill 1500 cells per day, which may result in frames with wall-to-wall capped brood.

As satisfying as it is for beekeepers to see swathes of brood, it can also be a warning of potential trouble in a few weeks’ time. On average, when a mama mite slips into a nearly-capped worker cell, she will emerge 12 days later along with 1 to 3 additional, mated daughters ready to start their own breeding cycles.

Adult female mites go through multiple rounds of egg-laying. They need energy to keep doing this, so they keep on biting pupae and adult bees, stealing vital nutrients, including vitellogenin each time they do.

But that’s not the only damage they do. Just as ticks carry diseases they can pass on while biting and sucking up some human blood, varroa mites can spread diseases to honey bees: a mite’s bite penetrates the bee’s exterior, leaving behind a never-healing wound — and the prolonged bite can spread viral diseases.

Once infected, these bees may have physical and functional malformations and substantially shortened lifespans. Further, while acting as nurse bees for subsequent brood, these diseases may be transmitted directly, bee-to-bee.

Why treat for mites in July?

Protecting your winter bees from varroa isn’t just a matter of making sure mite numbers are low when the winter bees are born. Because nurse bees infected with viral diseases earlier in their lives can inadvertently transmit while feeding the winter bees, it’s important to keep varroa numbers down almost two whole bee life-spans earlier.

Efforts at reducing varroa levels can take several weeks to have a successful impact. Which brings us back to July, a month when winter bees are a seemingly distant issue, but about only 8 to 12 weeks from the start of winter bee production (depending on your location). 

Reducing the varroa population in July interrupts the accelerating rate of parasitization and helps prevent nurse bees from becoming infected by mite-vectored disease early in life — making them less likely to pass on diseases while feeding the winter bees.

Long-lived and healthy winter bees well-supplied with vitellogenin can create the essential conditions for baby bees started in winter. Keeping them very well nourished, and surrounded by a thick mantle of heat-producing bees will ensure that there are enough bees left at the end of winter to get next year’s colonies off to a strong start. For more varroa treatment advice and beekeeping tips, explore our Beekeeper Guide.