Bigger Eggs, Bigger Queens? How the Queen Chooses Her Successor

One question that has often been in my mind when rearing new queens is whether the eggs or young larvae selected by the bees are better than the ones selected by the beekeeper.

I’ve long suspected this to be the case, and used it as an excuse when the products of my grafts have failed to mate well, been short-lived, or been quickly superseded by the colonies they were introduced to.

But now I’ve found a real excuse for my ham-fisted attempts at grafting!

The received wisdom

The received wisdom was that the quality of queens depended on environmental factors, including the age of the larva and the quality and volume of the royal jelly fed by the nurse bees. That in turn depends on the quality of the nectar and, particularly, the composition of the pollen the colony is foraging on and that is available to the nurse bees.

However, it has been found that when a colony is preparing to divide and reproduce itself by swarming, and builds queen cups that are larger than worker cells, the queen lays significantly bigger eggs in those cups (Wei et al. 2019¹).

That bigger eggs make bigger queens might seem a no-brainer, but the question of how the larger eggs come about hadn’t been asked before. The researchers tested the idea that, as well as the environmental effect, there is a maternal effect on queen production – that the mother queen herself plays a part.

The study

Queens were given cells of different sizes and shapes, matching queen cells and worker cells, so the researchers could compare eggs laid in queen-sized cells with eggs laid in worker-sized cells.

• Six hours after laying, some of the eggs were measured and weighed. Across 3 colonies, 152 eggs were examined, and those from the queen-sized cells were significantly heavier, longer and thicker than those from worker cells.
• Other eggs were moved into artificial queen cells without being touched (the plastic base of each cell was moved), and some worker-cell eggs were left until the larvae were 2 days old before being moved in the same way.
• All the queen cells were reared in the same queenless colony. Sixteen days later the new queens were collected as they emerged and weighed.

The trial was repeated with 5 colonies over 2 years. Queens from eggs laid in queen-sized cells were the heaviest in all 5 colonies, and significantly heavier than queens from worker-cell eggs in 3 of them – about 259 mg against 235 mg on average.

The paper’s figures showing the cells and the queen weights are worth a look: see the original paper.

OK so far, but so what?

Gene expression analysis found several genes that were expressed differently in queens from the bigger eggs. A disproportionate number of them are involved in the key traits that separate queens from workers:

• hormonal signalling;
• body development;
• immune pathways.

So egg size influences the shape and physiology of the queen that emerges. Together with the finding that queens lay larger eggs in queen cells, this shows both a maternal effect on how the queen develops, and that the mother queen plays a more active role in producing new queens than had been realised.

So how does she do it?

The authors don’t suggest there is a special class of “queen eggs” – the egg weights followed a single, continuous spread. Instead, they suggest that a laying queen has more than one egg ready at any one time and may choose the largest one for a queen cell. Another possibility is that she pauses before laying in a queen cell, since a delay in laying is known to produce bigger eggs with more yolk protein.

Either way, it seems queens can select larger fertilised eggs for queen cells. We already knew that a queen measures a cell with her front legs and withholds fertilisation when she lays in a larger drone cell. This is the first evidence that she can also choose between fertilised eggs, and that she can tell a queen cell from a worker cell.

Does size matter?

It could matter a great deal for the colony. Several authors have reported a link between queen weight and the number of ovarioles and egg-laying capacity, and one has even reported a link between queen weight and the colony’s honey crop.

There is also good evidence that queens reared from younger worker larvae tend to be larger, with more ovarioles and greater sperm storage, and may mate more often. That suggests size may partly be a marker of how well the queen developed, rather than the cause of her quality in itself.

Do bigger queens live longer?

This is where things are much less clear-cut. A queen’s reproductive quality declines with age, and her stored sperm – essentially a lifetime’s supply collected when she mates – is fundamental to keeping her fertile. But I couldn’t find good evidence that being bigger, on its own, makes a queen live longer. Her lifespan is tangled up with her age, nutrition, mating success, sperm storage, the colony’s condition and her genetics.

So the picture I take from the research is something like this:

Better larval nutrition and development → a larger queen → better reproductive organs and better mating → more eggs and a stronger colony.

Size may simply be the visible sign of a queen that developed well. Which brings me back to grafting: perhaps the bees – and the queen herself – really do know best when it comes to choosing the egg.

Reference

1. Wei H, He X, Liao C et al. (2019). A maternal effect on queen production in honeybees. Current Biology 29: 2208–2213. doi.org/10.1016/j.cub.2019.05.059