Drone

Drones are male honeybees. Male honeybees develop when the queen bee lays unfertilized eggs.

Photograph by Waugsberg licensed under Creative Commons.

Drone genetics
It is not clearly understood what prompts a honeybee queen to lay an unfertilized egg versus a fertilized egg. Honeybee eggs hatch regardless of whether they are fertilized. Drones develop only from unfertilized eggs. Unfertilized eggs are haploid in origin, which means that they contain only 16 chromosomes from their mother. The drones that a queen lays, therefore share a very similar genetic makeup.

All chromosomes contain hereditary units called genes. The specific place on a chromosome where particular genes are found is called a locus. All the forms of a gene that might occur at a locus are called alleles. Drones can carry only one type of allele because they are haploid; thus, they are called hemizygous.

Variety in bees is increased when a queen produces an egg. During this time, pairs of chromosomes in cells that are destined to become eggs exchange segments. In this process (meiosis), the chromosome number of germinal eggs is halved. This process results in a haploid egg, with chromosomes having a new combination of alleles at the various loci.

There is much debate in the scientific literature about the dynamics and apparent benefit of the combined forms of reproduction in honeybees. The drones have two reproductive functions. They convert and extend the queen’s single unfertilized egg into about 10 million genetically identical male sperm cells. Secondly, they serve as a vehicle to mate with a new queen to fertilize her eggs. Female worker bees, develop from fertilized eggs and are diploid in origin, which means that the sperm from a father provides a second set of 16 chromosomes for a total of 32 – one set from each parent. Since all the sperm cells produced by a drone are genetically identical, sisters are more closely related than full sisters of other animals where the sperm is not genetically identical.

A laying worker bee will exclusively produce unfertilized eggs, which develop into drones. As an exception to this rule, laying worker bees in some sub-species of honeybees may also produce diploid (and therefore female) fertile offspring in a process called thelytoky.

In honeybees, the genetics of off-spring can best be controlled by artificially inseminating the queen.

Anatomy
Drones are characterized by eyes that are twice the size of those of worker bees and queens, and a body size greater than that of worker bees, though usually smaller than the queen bee. Their abdomen is stouter than the abdomen of workers or queen. Although heavy bodied, drones have to be able to fly fast enough to catch up with the queen in flight.

Drones are stingless.

Role
The drones’ main function is to be ready to fertilize a receptive queen. Drones in a hive do not usually mate with a virgin queen of the same hive because they drift from hive to hive. Mating generally takes place in or near drone congregation areas. It is poorly understood how these areas are selected, but they do exist. When a drone mates with its sister, the resultant queen will have a spotty brood pattern (numerous empty cells on a brood frame); again it is not clearly understood whether this is from higher mortality of the larvae, or by removal of these larvae by nurse bees.

Several drones mate with a virgin queen on her mating flights a good distance away from the hive. Mating occurs in flight, which accounts for the need of the drones for better vision, which is provided by their big eyes. Should a drone succeed in mating it will soon die because the reproductive organ and associated abdominal tissues are ripped from the drone’s body at copulation.

Honeybee queen breeders may breed drones to be used for artificial insemination or open mating. A queen mating yard must have many drones to be successful.

In areas with severe winters, all drones are driven out of the hive in the fall. A colony begins to rear drones in spring and drone population reaches its peak coinciding with swarm season. The life expectancy of a drone is about 90 days.

Behavior
Drones never exhibit typical worker bee behaviors such as nectar and pollen gathering, nursing, or hive construction. Since the worker bee’s stinger is a modified ovipositor (an egg laying organ), the drone is defenseless and can not defend the hive. This has led the drone to be considered as a canonical example of a worthless member of a society. Although the drone is highly specialized to one function, mating and continuing the propagation of the hive, it is not completely without side benefit to the hive. All bees, when they sense the hive’s temperature deviating from proper limits, either generate heat by shivering, or exhaust heat by moving air with their wings — behaviors which drones do share with worker bees.

Drones fly in abundance in the early afternoon and are known to congregate in drone congregation areas a good distance away from the hive.

The information on this page has been reproduced from www.wikipedia.com. Copyright acknowledged.