Molly’s bees: shot brood and laying workers

Thanks to everyone who participated in the diagnosis of Molly’s honey bee colony. Overall, I thought the answers were impressive—both thoughtful and nuanced. Many of you agreed with my own assessment of shot brood, but others mentioned issues I hadn’t even considered. It was a great learning experience for many, including myself.

I emailed my opinion to the owner and her friend before I decided to post the photos, so a couple people out there can vouch for what I’m saying.

The uncensored answer

I’m always in a hurry, often with dozens of pending comments to answer, so I tend to go as fast as I can. This time, I glanced at the photos and immediately concluded “inbred queen.” But later, I second-guessed myself. The more I looked at the photos, the more I wasn’t sure of what I was seeing.

I spend hours each week identifying bees on iNaturalist.org, and from that experience, I’ve learned how difficult it can be to evaluate a three-dimensional object in two dimensions. The same problem applied here. It was hard to tell if the cappings were flat like workers or mounded like drones, as many of you mentioned.

The shape of the nest

At any rate, when I first looked at the photos, I was pretty sure I was seeing at least some capped worker brood. Based on the overall shape of the brood nest—more or less football shaped with honey stored in the upper corners—I concluded that, at least for a while, the colony had a fertile, laying queen.

However, the shot brood pattern suggested inbreeding, meaning the queen was probably mated with close relatives. With bees, inbred queens yield what is called diploid drones—drones with two sets of chromosomes. They occur because what really determines the sex of bees is not the number of chromosomes but whether or not the genes at the sex locus are the same or different. Different forms of the same gene are called alleles, and healthy populations have a selection of alleles available for each gene.

When inbreeding occurs, there are fewer alleles in the mix, so any randomly selected pair of chromosomes has a higher probability of having two of the same allele at the sex locus. When the two sex alleles are the same, you get a drone with two sets of chromosomes instead of the usual one. (You can follow the above link for a more detailed explanation of sex determination in bees.)

Shot brood yields slow growth

More to the point, diploid drones do not reach adulthood. The worker bees detect their presence in the brood cell and pluck them out. The result is called shot brood, which is basically a normally-shaped nest with a bunch of “empties” scattered around. The more inbred the queen, the more empties you will see.

When you have a huge number of diploid drones, the queen will not be able to produce enough brood to maintain the colony. The colony population doesn’t grow so there are not enough bees to do all the work. This, I believe, was the initial problem in Molly’s colony.

What happened next

Please bear in mind that this was only a guess on my part. But assuming the hive was queenright, as least for a short time, what happened next?

From subsequent photos, it seems that laying workers took over the colony. The queen may have died, her pheromone levels may have been low, or she may have been an intercaste with assorted queenly deficiencies.

An intercaste queen is one that was raised from an older larva. Such queens don’t receive an exclusive diet of royal jelly from the get-go, so they are often small and only marginally competent to lead a colony. Although the workers replace intercastes quickly, they can sometimes provide an important bridge that keeps the colony alive. With any luck, the workers will build another queen from one of her eggs.

At any rate, that didn’t apply here and laying workers took over with a vengeance. Laying workers begin to develop after about three weeks of queenlessness, three weeks of insufficient queen pheromone, or the same length of time without open brood. In the next group of photos you can see eggs dropped into cells willy-nilly, all of which will develop into drones.

In summary, I believe that inbreeding caused the initial problem, but laying workers stepped in to finish it off.

The EFB question

Many of you raised the possibility of European foulbrood. I dismissed that idea, perhaps prematurely, because I have rarely seen EFB take over a colony from a package so quickly. Usually when I see it aggressively ravage a new installation, it came with a nuc rather than a package. That’s not to say it can’t happen, but I didn’t get that feeling in this case. Still, it’s a valid consideration because shot brood and EFB-infected brood can look amazingly similar. If you are unsure, testing for EFB would be the next step.

In the end

Ultimately, Molly combined her bees with a strong nuc, and it sounds like they are doing fine. Thanks to everyone for participating, and a special thanks to Molly for allowing us the opportunity.

Rusty
Honey Bee Suite