1. Biological Development Cycle

Egg stage: from day 1 to day 3, the egg develops within the cell. At laying it weighs approximately 0.16 mg. It contains a pre-larva that eventually breaks through the egg membrane. Larval stage: from day 4 onwards, the egg hatches. The larva first receives royal jelly for three days, then brood food until capping, which occurs on day 10 and forms a convex capping. The larva continues developing until day 13, spins its cocoon using its silk glands, and can reach up to 350 mg, approximately 2,200 times its initial weight.

Pupal stage: from day 14 onwards, the larva becomes a pupa and continues developing until day 24. Eye colour changes progressively from very pale pink to dark violet; wings appear from day 16, reach their final shape around day 23, and body hair becomes visible at this stage.

Emergence: the drone emerges on day 24 by opening the capping. It then weighs between 200 and 230 mg. This development can be prolonged by 1 to 4 days if food quality is poor or temperature is too low. Eye colour at the pupal stage allows the age of the brood to be estimated precisely.

Food: during the first days after emergence, the drone is fed by workers with a mixture of brood food and honey. It then begins to feed itself directly from the honey stores. First flights: these take place between days 5 and 8. Drones may be accepted into any hive, which promotes genetic diversity and limits inbreeding. From days 12 to 15 onwards, they begin attending drone congregation areas.

Sexual development: it begins very early, as early as day 5 after egg laying. The testes develop until day 21, then sperm migrates to the seminal vesicles from day 23 onwards. The reproductive organs are considered fully developed a few days after emergence, and sexual maturity is reached between days 12 and 15 after emergence, approximately 40 days after egg laying. The drone remains fertile until its death.

Drone congregation area: virgin queens fly to drone congregation areas (DCAs), aerial zones of 30 to 200 m in diameter situated between 10 and 40 m in height. These areas persist from year to year and can gather thousands of drones, even in the absence of a queen. When a queen enters the zone, the drones pursue her in a swarm in an attempt to mate with her. Matings take place mainly in the afternoon, in fine weather, with little wind and a temperature above 18 °C. Drones may travel several kilometres to reach these areas and generally remain faithful to the same location.

Drone eviction: at the end of the season, as resources dwindle and the mating period is over, workers expel the drones from the hive and may kill them. Highly sensitive to cold, drones die rapidly. Queenless colonies sometimes retain them for longer.

2. Morphology

The drone is heavier than a worker and slightly lighter than a queen. Its considerable size, powerful thorax, and very large compound eyes give it strong flight and orientation capabilities. Its antennae have one more segment than those of female bees, which enhances its sensory capacity.

It has no sting, no wax glands, and no pollen-collecting organs. Its tongue and mouthparts are less developed than those of the worker. A large portion of its abdomen is occupied by the reproductive organs: testes, seminal vesicles, ejaculatory duct, bulb, and endophallus. During mating, the endophallus detaches, causing the drone's death a few minutes later.

3. Genetic Selection

This chapter presents the principles of genetic selection as applied to beekeeping. Its aims include preserving breed purity, improving productivity, reducing swarming impulse and aggressiveness, enhancing resistance to diseases or varroa, increasing precocity, and improving suitability for visiting specific flowers. Haploid – diploid: workers and queens develop from fertilised eggs and are diploid, with two sets of chromosomes. Drones develop from unfertilised eggs and are haploid, with a single set of sixteen chromosomes derived from the queen.

Genes and alleles: a given trait is determined by genes located on a chromosome pair. The different possible versions of a gene are called alleles.

Dominance and recessiveness: when two alleles are identical, the trait is homozygous. When they differ, they may be co-dominant or follow a dominant/recessive relationship, with the dominant allele masking the expression of the recessive one.

Homozygosity and heterozygosity: homozygosity facilitates the stable expression of a trait, but it is rare in nature. It is often sought through artificial insemination to fix a gene, at the risk of reducing genetic diversity.

Fixing a gene: artificial insemination and sometimes inbreeding over several generations make it possible to obtain the desired alleles, but these methods require care and patience.

Selection programme: the author recommends having ideally at least twenty colonies, preferably fifty. The selection plan comprises five steps: defining the desired traits, selecting the colonies that best meet the criteria, assessing these colonies over a given period, rearing queens and drones from the best lines, and then replacing unselected queens with daughters from the chosen lines, while regularly introducing new genetic stock.

4. Managing a Drone Comb Colony

Management of a drone colony depends on the intended purpose: populating a mating apiary, supplying a mating station, or producing drones for artificial insemination. In all cases, rearing must be planned, the required number of drones estimated, and colonies selected with care.

Number of drones required: it is always necessary to plan for considerably more than the theoretical minimum. A Dadant drone frame yields approximately 2,000 drones, theoretically sufficient to mate around a hundred queens, but a proportion will not reach sexual maturity, will drift too far, or will be predated.

Rearing conditions: strong, healthy colonies well supplied with honey and pollen must be used, reinforced with emerging brood to ensure an adequate number of nurse bees. Colonies must have a low varroa infestation level, hence the importance of appropriate treatments, whether mechanical or chemical.

The drone frame: it can be made by cutting a sheet of foundation to two thirds of its height and attaching it to a frame placed at the edge of the brood nest. The bees then build worker cells on the upper two thirds and drone comb on the lower third. Ready-made drone frames are also commercially available.

Method for a mating apiary: the objective is to saturate the local area with drones from selected colonies. Drone frames are introduced into the chosen colonies, ideally the previous year or in spring before the first nectar flow. The egg-laying pattern is then monitored, freshly laid or larval frames are moved to the centre of the brood nest, additional drone frames are added, the colony is strengthened with emerging brood, and a generous supply of honey, pollen, and protein fondant is maintained. The offspring obtained in this way are hybrids and correspond to F1 queens.

Method for a mating station: isolated mating stations allow controlled matings by drones from selected lines, provided exclusively sister colonies are used. Approximately fifty days before the drones are needed, drone frames are introduced into the source colonies. Once capped, they are used to establish queenless drone colonies, which are transported to the station along with food frames, emerging brood, open brood, and drone frames. Frames are renewed in stages every eight days, queen cells are removed, and protein feeding is maintained. Once production is complete, the colony can be requeened.

Method for artificial insemination: since drones readily drift from one hive to another, they must be reared under confinement to guarantee their origin. The principle is similar to the previous method, but the drone colony is kept away from other hives and fitted with a raised floor with a queen excluder. Drones are allowed out at controlled times, at least twice a week, and dead drones are removed from the grid. Feeding is maintained continuously until collection.

Drone collection: fifteen days after emergence, drones are ready for semen collection. They can be caught using a meshed entrance placed on the hive or collected early in the morning when they are calmer. They must be kept warm, transported quickly, and placed in the laboratory in a flight cage heated to approximately 30 °C. Cooling below 25 °C or excessive stress durably impairs semen quality and eversion capacity.

Semen collection: several techniques exist. Full eversion is achieved by pulling on the head, then applying gentle pressure and rotation to the abdomen. Only the cream-coloured semen should be collected, without the white mucus, using a capillary tube mounted on a syringe, under sterile conditions. A drone produces up to 1.25 microlitres of semen, but approximately 1 microlitre is generally recoverable. The capillary tube must be sealed with vaseline, and the semen can be stored for up to three weeks at around 18 °C.

Having drones early in the season: the author recommends using drone frames built up and stored over winter, placed in spring at the centre of the brood nest, accompanied by a pollen frame from the previous year and protein fondant, with continuous feeding. Another option is to use a drone-laying colony derived from a late unfertilised queen kept under confinement so that she lays only drones.

Maintaining drones late in the season: two strategies are proposed: simulating a nectar flow by daily feeding with 50/50 syrup, or making the colony queenless, since queenless colonies retain their drones for longer. In the latter case, open brood must be introduced regularly and any queen cells subsequently destroyed to prevent the appearance of laying workers.

5. The Effect of Varroa on Drones

The document reports studies comparing unparasitised drones, drones parasitised by one female varroa mite, and drones parasitised by two female varroa mites from the larval stage onwards. Unparasitised drones: approximately 7,450,000 spermatozoa on average; mean flight performance 6 min 48 s, maximum 27 min 27 s. Drones parasitised once: approximately 4,200,000 spermatozoa, a decrease of 44%; mean flight performance 6 min 55 s, maximum 22 min 15 s. Drones parasitised twice: approximately 3,550,000 spermatozoa, a decrease of 53%; mean flight performance 2 min 16 s, maximum 6 min 01 s. Varroa therefore substantially reduces drone sperm production. The impact on flight performance is most pronounced when two female varroa mites have parasitised the same individual, with an average reduction in flight performance of approximately 67%.

6. The Bumblebee (Bombus)

Description: the bumblebee is a large, stocky, very hairy foraging insect that can reach 32 mm in length. Its body consists of a small head with antennae, a very robust thorax, and a short abdomen whose first segment is fused with the thorax. Its flight is loud, and it has three castes: queen, workers, and males.

Biological cycle: unlike the honeybee, the bumblebee colony is annual and less organised. Only young mated queens overwinter. In spring they establish a nest, often in an old underground rodent burrow, which they line with moss, leaves, grass, or hair. The queen constructs two wax cells, one for the first eggs and one for storing nectar. The eggs hatch after approximately four days, the larvae develop together for a week, then each spins its own cocoon before becoming a pupa. After approximately a further thirteen days of incubation, the first workers emerge and gradually take over the colony's tasks. A colony reaches a maximum of nearly 500 individuals, but often comprises fewer than 200.

At the end of the warm season, the queen lays unfertilised eggs giving rise to males, then further eggs destined to produce future queens. After mating, these young queens accumulate reserves and seek a dry shelter in which to overwinter, while the old colony disappears with the death of the founding queen and her workers.

Defence behaviour: the bumblebee is not aggressive. It stings only in self-defence or to defend its nest. Only females possess a sting. Since this sting is not barbed, they can sting multiple times without dying. Most stings produce a local reaction, but allergic reactions are possible.

Mating behaviour: this varies between species. In some, males wait near the nest for a virgin queen to emerge. In others, they establish a route marked with pheromones and patrol it while waiting for a young queen. Mating takes place, in most species, on the ground.

Ecological importance: thanks to its body hair and its tolerance of difficult weather conditions, the bumblebee is an excellent pollinator. It can forage from 8 °C onwards, in low light, despite wind or rain. Temperatures above 35 °C, however, bring foraging activity to a complete halt. Its role in the conservation of natural habitats is essential.

Food: the bumblebee feeds primarily on nectar and pollen. It can produce small quantities of honey, with a more pronounced flavour than that of the honeybee. The larvae are fed with a diet rich in pollen, protein, minerals, and vitamins.

The most common species: the text mentions in particular the early bumblebee (Bombus pratorum), the garden bumblebee (Bombus hortorum), the common carder bee (Bombus agrorum), the red-tailed bumblebee (Bombus lapidarius), and the buff-tailed bumblebee (Bombus terrestris).

Economic role: the buff-tailed bumblebee is widely used for greenhouse pollination, particularly for tomatoes, a plant whose pollen must be released by vibration. Introduced into greenhouses from 1988 onwards, it is now also used for strawberries, blueberries, raspberries, melons, courgettes, peppers, aubergines, pears, apples, and seed production. Its use improves fruit quality and commercial yield.

► Everything about the drone – Read the article

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See also:

• Drone rearing
• Rearing drones
• Introduction to bee genetics
• Cryopreservation of drone semen
• Drone frame