The drone-laying colony

It may happen, for example during the first spring inspection, that one encounters a moribund colony with no food reserves, with frames showing scattered brood of the male type … What has happened?

Figure 1: Drone-laying colony: very small population, scattered drone brood, no worker brood, low food reserves, no visible queen, deformed combs, drone cells.

1. Reminder of some basic notions

The queen’s main role is to lay eggs in order to enable the well-known population dynamics within the hive. The laying of fertilized (diploid) eggs leads to the emergence of workers; the laying of unfertilized (haploid) eggs produces males. The queen’s egg-laying depends on multiple (epigenetic) factors such as nectar/pollen intake and the amount of royal jelly offered to her by the nurse bees of her retinue, the space available for brood, the ambient temperature inside the hive, the season, etc.


Figure 2: Blue curve: population dynamics of worker bees over the beekeeping year. At the end of December, the colony numbers 10'000 workers in the winter cluster; at the end of June, the colony numbers 50'000 individuals.

The queen also releases many pheromones that promote the colony’s social cohesion and, thanks to a subtle balance, modulate behavioral changes in workers and perhaps also in males. For example, the queen mandibular pheromone inhibits sexual development in workers and prevents them from rearing another queen. Similarly, pheromones produced by the brood play a major role in many worker activities: foraging, wax secretion and comb building, swarming, queen rearing, acceptance of a new queen, etc. Workers also release pheromones whose composition and effects on their behavior vary with age polyethism (1). We recall that ethyl oleate (EO), produced by foragers, is a molecule that plays an essential role in the maturation and transition of younger bees: it acts as a chemical inhibitor that delays the onset age of foraging. Vitellogenin is a protein that is highly present in winter bees; it stimulates their immune system and their chances of winter survival. It also modulates the type of foraging during the beekeeping season.


Figure 3: Vitellogenin: synthesis and actions.

(1) Polyethism is the division of labor in social animals. Two types are distinguished: caste polyethism (queen, worker, male) and age polyethism (the different “jobs” of the worker throughout her life).

2. Supersedure

When egg-laying and pheromone production decline with the queen’s age, she is replaced through supersedure, without the colony swarming. Young workers that perceive the decline in egg-laying and pheromone secretion select a fertilized egg, often in the middle of a frame, and progressively build a queen cell from that original worker cell (2). From this egg a larva will hatch, which will be fed exclusively with royal jelly during the 6 days preceding the capping of the cell. The young virgin queen will emerge 16 days after the egg was laid. The mating flight will allow her to store, for several years, the spermatozoa of reproductive males and thus to lay about 500'000 fertilized eggs during her life. During supersedure, it may happen that the new mated queen cohabits for some time with the old queen, who will eventually be eliminated. But if supersedure occurs late, at the end of the season, there will no longer be (enough) drones to fertilize the virgin queen, which will create problems at the end of winter…

(2) Cell: masculine or feminine (Latin alveolus, small basket)


Figure 4: Queen cells.

3. Emergency queen rearing

It may happen that the queen disappears suddenly (if, for example, the beekeeper accidentally crushes her). Replacement of this queen follows a very different course. As soon as they feel queenless, the workers initiate queen rearing from several larvae in a process of colony rescue. Often a first queen cell is started, urgently, from the cell containing a 2–3-day-old larva, then other queen cells are drawn from cells with much younger larvae. Queens raised from “older” larvae, poorly selected in the urgency, often perform less well than those raised from the youngest larvae, identified after a few hours of reflection. The composition (pure royal jelly) and the amount of food provided to these larvae chosen in “serenity” are optimal, and the development of royal organs (reproduction and pheromone secretion) is ideally modulated by epigenetics. The experienced beekeeper will therefore remove the first capped queen cell(s) and keep only two queen cells that are still open (younger) and more likely to receive the best food during the 6 days of the larval stage.

Supersedure and rescue therefore enable the colony to cope with pathologies affecting egg-laying or the sudden disappearance of a queen, thanks to processes that are well understood by biologists and beekeepers.


Figure 5: The queen of this colony died suddenly. The bees of this vigorous hive immediately started intensive queen rearing.

4. Queenless colonies and drone-laying colonies

Sometimes a colony that has remained queenless no longer has eggs or very young larvae available to start queen rearing. The example of a mating flight that ends badly is often mentioned. The young virgin queen leaves the hive to be fertilized, but on her return from the nuptial flight she is eaten by a bird. The result: the colony becomes queenless, without any open brood. Another example is a queen that tolerates formic acid treatment poorly: first she stops laying, then she dies, leaving the colony without fresh brood. In these situations, the level of queen pheromones drops abruptly, and the diffusion of pheromones by the remaining capped brood decreases as the last workers emerge. Gradually, the inhibition of reproductive organ development in workers disappears, and one or more workers become pseudo-queens (their worker morphology does not change), with ovaries that progressively develop and unfertilized eggs (haploid oocytes) that differentiate in preparation for being laid. This epigenetic change can take a variable amount of time, and the queenless colony, if it is not identified early enough, will become drone-laying within a few days or after several weeks. These pseudo-queens will also start releasing queen-like pheromones. The level of these pheromones will influence the development of reproductive organs in other workers, which would explain why a drone-laying colony generally includes only one or a few laying workers.

Figure 6: Reproductive system in the queen. The ovaries allow the progressive maturation of the 500 000 oocytes that the queen will lay during her long life.

These pseudo-queens have not been fertilized and never will be. Indeed, epigenetics modulates the queen’s nuptial flight, which occurs only during the 2–3 weeks following the queen’s emergence. A worker that becomes a pseudo-queen will not be stimulated to perform a mating flight. Moreover, the late and sometimes incomplete maturation of her reproductive system prevents fertilization, even artificial, and the storage of drone sperm. These pseudo-queens are therefore condemned to lay sterile eggs from which only males emerge. This situation will lead to the collapse of the colony, because it no longer has the possibility of compensating population losses due to natural mortality of workers. Varroa will multiply in this sole drone brood available to it. A foundress female that enters a drone cell will produce about 2.7 young females versus 1.1 in a worker cell. The reproduction rate of Varroa there is therefore almost three times higher! The mites will further accelerate the decline of this drone-laying colony by feeding on the fat body of the last nurse bees and by inoculating their cohort of viruses into the agonizing colony.

The diffusion of pheromones by pseudo-queens has another consequence for the colony’s survival. Introducing a frame of open brood (presence of eggs/larvae) into this colony impregnated with queen-like pheromones never induces the rearing of a new queen. A queen breeder knows perfectly well that a colony must be queenless to draw a queen cell and rear a queen. A drone-laying colony is not a queenless colony since it contains one or more pseudo-queens! It is therefore almost impossible to save a drone-laying colony by introducing open brood. Likewise, if one attempts to introduce a laying queen into this pseudo-royal colony, that queen will not be accepted by workers impregnated with the pheromones of laying workers. It is true that introducing a “ready-to-emerge” queen cell can succeed, but this strategy cannot work in autumn and at the end of winter, because queen fertilization is impossible at those times due to a lack of drones. Consequently, it is not recommended to persist in trying to save a drone-laying colony at all costs. It is better to eliminate it and focus efforts on other colonies that have a future. By contrast, a queenless colony has no queen (nor pseudo-queen), thus no queen pheromones, and if a frame of open brood is introduced into such a colony, queen rearing will start immediately.

Figure 7: The worker population is clearly insufficient to cover the frames of the hive. Food reserves are absent. Presence of open brood in deformed and enlarged cells. The capped brood is domed, sheltering drone larvae. Without looking for the queen, one can certify that the colony is drone-laying.

5. Management of queenless colonies

A colony may become queenless:

After swarming, when the new queen is lost after her mating flight
After an unintended flight and failure to return to the parent hive during queen marking
After an unsuccessful attempt at supersedure of an old queen or an unsuccessful rescue attempt
After formic acid treatment
After an unsuccessful introduction
After an accident (poor handling by the beekeeper)

When the hive is opened, the buzzing of the workers, possible aggressiveness, the absence of open brood, and the absence of queen cells suggest a queenless colony. Observing capped worker brood suggests that the colony has been queenless for less than 3 weeks, because it takes 21 days for all worker brood to emerge. To verify that the colony is indeed queenless, the beekeeper can introduce a frame of open brood without bees from another colony. If, upon inspection 3 days later, the presence of one or more queen cells is noted, the colony is indeed queenless. If, on the contrary, no queen cells are started, the colony very probably contains a queen (young, not yet mated or not yet laying; older, but not or poorly mated). Brood presence must be checked again 2 weeks later: if brood is still absent, one must carefully look for a small virgin queen (or an old queen that has stopped laying), which must be removed before introducing a frame of open brood or possibly a laying queen (acceptance is uncertain and depends on the season).

A colony can remain queenless without becoming drone-laying:

Usually, after some time (the time required for the lack of queen pheromones to allow the development of reproductive organs in one or a few workers), the colony becomes drone-laying. Sometimes a grain of sand jams the gears of this physio-pathological process and the development of ovaries and other pheromone glands fails (ineffectiveness of epigenetics in workers that are too differentiated or too old, no longer able to develop oocytes or gametes). These “pseudo-royal workers” do not lay, but still secrete a small amount of queen pheromones, preventing other workers from becoming layers…

Another situation is one in which the old queen has exhausted her stock of oocytes (unfertilized eggs). Normally, workers supersede a queen that is not satisfactory. It is possible that the cessation of egg-laying occurs during overwintering and that supersedure is impossible within the winter cluster. The following spring, the queen will no longer lay, but she will still release her pheromones. The colony is not queenless (the queen is present), but brood is absent.

If a queenless colony is healthy but too small, it can be united with another healthy colony to strengthen it, or it can be shaken out in the apiary so that the workers drift into neighboring colonies.

6. Management of drone-laying colonies

A colony may become drone-laying:

after a more or less prolonged period of queenlessness, with no open brood available to initiate rearing. One or more workers become laying workers and play the role of a queen.
when the old queen has exhausted her stock of spermatozoa and can no longer fertilize her eggs. The queen then becomes drone-laying and lays unfertilized eggs. There is no laying worker present in the hive.

When the hive is opened, the colony population is very small and only drone brood is present, laid by workers: not compact, scattered, often with multiple eggs in the cells, sometimes attached to the walls. It seems that the length of the laying workers’ abdomen does not allow them to place the egg at the bottom of the cell as a properly developed queen would. It is known that the queen lays only after a meticulous inspection of the cell and that, faced with the slightest impurity (for example an egg already present), she does not lay there and inspects another cell… Such inspection behavior seems deficient or absent in laying workers…

The presence of laying workers (pseudo-queens) releasing queen-like pheromones does not allow the introduction of a laying queen. That queen will be eliminated by the workers, as happens when one introduces a queen into a colony that already has one. Queen rearing from open brood introduced into the hive does not start either, because the presence of inhibitory pheromones released by laying workers prevents the colony from drawing a queen cell from a very young larva.

Sometimes the level of pheromones released by these pseudo-queens is not optimal and workers draw, in the vain hope of saving the colony, a cell from a drone larva (see photo at the beginning of the article). This larva does not develop like one in a normal drone cell, and the “king” aborts in the cell or dies “in utero.” The dead larva will no longer secrete any pheromones, and its influence on the colony will be at best uncertain, if not null. Proof of this is the fact that this queen cell sometimes remains intact until the colony collapses completely. A too-quick inspection of this colony can be falsely reassuring: one observes a queen cell and thus thinks supersedure is underway, while the colony is already doomed…

A drone-laying colony therefore has little chance of survival, especially since it is often carrying infectious pathologies (bacterial, fungal, viral) that may be transmitted to other healthy hives through robbing. Any attempt to save it will be doomed to failure, and the beekeeper is far better off caring carefully for other healthy colonies. A drone-laying colony should therefore be eliminated or brushed off at a distance from neighboring colonies.


Figure 8: Brood of a drone-laying colony: deformed cells with domed drone cappings, heterogeneous mosaic brood, multiple eggs in cells, larvae of different ages.

7. Many questions remain open

How long does it take before a queenless colony becomes drone-laying? Does this depend on population size? Is it related to the presence or absence of brood?
Why do some queenless colonies never become drone-laying?
How many workers become laying workers, i.e., develop their ovaries and begin to lay? One, two, three, or many more? What does this number depend on?
Do laying bees differ morphologically from other workers?
Why does a drone-laying colony sometimes raise a king in a “queen cell”?

Warning! Do not confuse the brood of a young queen that has just started laying in a mating nucleus with drone-laying brood: it may happen that, with hyperfunctional ovaries or for lack of space, she lays several eggs in one cell. This is rather a sign of a high-quality queen!


Figure 9: Brood of a young queen freshly mated in a mating nucleus: several eggs at the bottom of cells in a recently built and undeformed comb (white wax). No larva visible yet, no brood with domed cappings.

We can return to the initial question: “It may happen, for example during the first spring inspection, that one encounters a moribund colony with no food reserves, with frames showing scattered brood of the male type… What has happened?”

One hypothesis would be that the queen did not tolerate the second summer treatment (formic acid) and that supersedure that occurred too late (absence of reproductive males) did not allow fertilization of the new queen, who remained virgin and is not able to lay.

Another hypothesis is that of an old queen that has exhausted her stock of spermatozoa at the end of the season; the following spring she will lay unfertilized eggs. During the autumn inspection and preparation for overwintering, checking for the presence of a current-year queen and compact, homogeneous brood is the guarantee of successful development of a promising colony for the coming season.

8. Conclusion

When inspecting a hive, the beekeeper must always answer the question: “Is there a queen in this colony?”.

The presence of open brood with single eggs in cells makes it possible to certify that a queen was present and laid less than 3 days ago.
The absence of open brood means that there has been no laying for at least 9 days; one must look for the queen to be certain not to have crushed her during the previous inspection. If the queen cannot be found, one must look for the presence of one or more queen cells that the colony may have drawn through supersedure or rescue (see swarming).
The absence of capped brood allows one to conclude that there has been no laying for at least 3 weeks. One must then determine whether the colony is queenless or already drone-laying.

If the colony is not queenless (which can be tested by introducing a frame of open brood without any queen cells being started within 3 days), one must wait for laying to resume (for example after formic acid treatments). If laying does not resume, one must find the queen and replace her.

If the colony is queenless and populous, one can attempt to save it by introducing a new queen or a frame of fresh brood(3). If this queenless colony is very small but healthy, it can be united with another healthy colony.

If the colony is drone-laying, one must have the courage—or rather the common sense—to remove it.

(3) Until the end of June/beginning of July, one can try to save a queenless colony by introducing a frame with eggs and open brood. From early July onward, the colony is saved by introducing a laying queen, because for natural rearing time is short before overwintering: queen emergence (~ 2 weeks), onset of laying (+ 2 weeks), worker emergence (+ 3 weeks), foragers’ first flights (+ 3 weeks, i.e., mid-September).

9. A few anecdotes

Anecdote 1 :

In May, a beekeeping advisor is called by a young beekeeper to help recover a large swarm that has been sitting on a branch for several days. The swarm, which had already begun to build the beginnings of combs, is easily hived onto 6 sheets of foundation.

3–4 days later, the foundation is fully built out, with irregularities, and very heavily laid: virtually all cells contain an egg! The queen’s presence was not sought given the abundant laying. A few days later, without having found the queen despite a careful search, the beekeeper takes workers from the 6-frame nucleus containing the swarm to populate the 20 Apidea mating nuclei she plans to take to a mating station. When introducing the queen cells (Day + 11) raised from the brood of a selected queen, it is noted that the sealed starts on the frames are under construction, but somewhat irregularly, with drone cells. At the check before transfer to the station (Day +13), the queen cells are empty and intact (they are not gnawed): the queens have therefore emerged correctly and the Apidea nuclei can be taken to the station.

After the 15 days spent at the station, the nuclei return to the lowland apiary. Open brood is present, which appears normal, and capped brood of the male type. The new F0 queen is located and marked. At the check 45 days after grafting, everything is back to normal: laying is homogeneous, the old drone brood has fully emerged, and the capped brood is only of the worker type.

What happened?

For an unclear reason, the initial swarm lost its queen before settling on the branch. As a reminder, a prime swarm leaves with a (old) queen. A secondary (and subsequent) swarm may leave with one or more queens. Thanks to trail pheromone marking, the cluster remained compact on the branch and the wax makers began to build (irregular) combs. One can think that the queen was old and no longer released many queen pheromones. Her disappearance lifted the weak residual inhibition and, as soon as the swarm felt queenless, workers took over, released replacement pheromones to stimulate the builders, became laying workers, and started laying unfertilized eggs. This epigenetic modulation probably explains the speed of construction and egg-laying on the six foundation sheets in the nucleus used to receive the swarm. Populating the Apidea nuclei introduced pseudo-royal workers among the sealed starts on the frames. It is known that a colony builds comb only if there are queen pheromones present. A queenless colony usually does not build. When the queen cells were introduced, the mini-colonies in the Apidea nuclei were impregnated with pheromones from the queens about to emerge from their protective cell. The queens emerged without problems and were accepted, because the population of an Apidea is often limited to <1'000 individuals. After their mating flight, the new queens greatly increased pheromone diffusion and the pseudo-queens progressively returned to the worker state through the well-known epigenetic modulation.

Conclusion:

A drone-laying colony contains an undetermined number of pseudo-queens. In the case above, one can estimate that pseudo-queens were numerous, since at least one was found in each of the 20 Apidea nuclei! Shocking, isn’t it?

Anecdote 2 :

As part of rearing an F1 queen in an Apidea nucleus at the apiary, the young laying queen is transferred to a 6-frame nucleus. The mating nucleus becomes drone-laying very shortly after becoming queenless. Workers begin queen rearing from a drone larva. At the expected time of emergence, they demolish the large cell and build another.

What happened:

One may presume that rearing an F2 queen did not succeed for an unclear reason (abortion of the larva in the queen cell leading to a drop in larval pheromones). A few workers take over the royal role and lay drone eggs. The bees draw a “queen cell” containing a drone larva whose diffusion of male pheromones disturbs the workers shortly before emergence and the cycle starts again…

Conclusion:

Pheromones are released by the three castes, but differ either in their molecular composition, or in their concentration, or both.

Anecdote 3 :

A swarm is recovered one week after leaving the parent hive. The bees had begun to build small combs on the tree branch; no eggs visible. The swarm is hived and quickly starts building out 6 sheets of foundation. The queen cannot be found! Comb construction is irregular with drone cells and drone-laying…

The beekeeper starts queen rearing and populates an Apidea nucleus with workers from the drone-laying colony. Construction of starts in drone cells and onset of drone-laying… yet the small colony accepts the queen cell introduced 3 days later, just before the emergence date; a queen emerges, mates, and after some time the drone brood is replaced by a completely normal laying of fertilized eggs.

What happened:

Although drone-laying, the small package of about 500 bees introduced into the Apidea nucleus accepts the queen cell and the queen that will emerge probably because of the diffusion of queen pheromones at high concentration relative to the pheromones emitted by the small number of laying (pseudo-queen) and non-laying workers. Once the young queen begins laying, the drone brood is progressively replaced as bees emerge.

Conclusion:

While it is difficult, even almost impossible, to introduce a queen into a drone-laying colony, it seems that a very small number of bees is gentler or more tolerant, probably due to weak impregnation by ambient pheromones. A well-known example: opening an Apidea nucleus is usually done without smoke or any protection, because this small population is not aggressive at all.

Anecdote 4 :

After spending the whole winter without any brood, a queenless colony accepts the introduction of a young laying queen in spring.

What happened :

The queenless colony formed a winter cluster to save the “fuel” used to maintain a minimum temperature for survival. Since the winter season is not conducive to rearing, there was no stimulation pushing workers to become laying workers. The colony remained queenless until the timely introduction of a laying queen.

Conclusion :

It is possible that a colony remains queenless for several weeks or months if climatic conditions are not very favorable to a rearing atmosphere.

Anecdote 5 :

A drone-laying colony is brushed off at a distance from the parent hive. When returning to the original location, the bees colonize a queenless colony in the apiary, which quickly becomes drone-laying in turn.

What happened?

The brushed-off bees were readily accepted by a queenless colony, probably because the laying workers were able to enter without being repelled by the guards. The brushed-off drone-laying colony was able to recreate a “social cohesion” at the expense of the queenless colony.

Conclusion :

In the absence of queen pheromones released by a functional queen, the balances between castes are unstable. One should think in terms of “pheromonal fragrances,” dear to perfumers, rather than a simple pure pheromone. Thus each colony has a particular “scent”…

Anecdote 6 :

A small drone-laying colony is brushed onto a white sheet at a distance from the parent hive, which remains in place. All the brushed-off bees return to the parent hive; not a single bee remains on the sheet.

Conclusion :

Laying workers or pseudo-queens are capable of flying.