The Drone Honey Bee

The male honey bees, the reproductive caste of the colony, develop through haploid/diploid parthenogenesis. The drones develop from haploid/ diploid unfertilized eggs produced by parthenogenesis or from diploid fertilized eggs having identical sex alleles, formed after sexual reproduction, with more probability when the queen honey bee mates with the drones of the same hives. Therefore, two types of drone honey bees, based on ploidy, are common in colonies, e.g. haploid or/and diploid. The number of drone honey bees staying in the colony varies according to protein resources and the strength of the worker honey bees. Generally, the haploid drone eggs/larvae laid by workers are removed by the nurse bee due to cannibalism. The above-mentioned eggs/larvae are marked with certain specific hormones that act as markers for cannabalic removal of the same. Further, the development of drones is influenced by colony temperature; hence overall development can be completed within 24-25 days. The purpose of drone life is to produce sperm and mate with the queen. The queen attracts the drone's honey bees toward herself with pheromones 9-ODA, 9-HDA and 10 HDA. The drone number and fertility depend upon the colony's environmental conditions, genomic possession and available food in the colony. The specific chapter provides deep insight into the development of drones, the biology of drones, the reproductive system, and the mating behaviour of particular castes. Subsequent chapters highlight morphometric characteristics of drones, development, mating, reproduction and artificial drone production.

The Drone caste exhibits specific diagnostic morphometric characteristics that facilitate its differentiation from other colony castes. Drone formation gets completed in about 24-25 days, with the first ten days in an open cell and the final 14 days under capped conditions. Furthermore, the drone caps are convex in shape. The Drone egg is measured about 1.49±0.12 (range 1.12–1.85) mm, the width is 0.35±0.02 (range 0.30–0.40) mm, and the volume is 0.10±0.02 (range 0.06–0.15) cubic mm. After hatching for the first three days, the larval weight is 0.11 mg, the 7th-day-old larva is 120 mg, 11th-day-old larva reaches a weight of 350 mg. An adult has a mean body length of about 1.5 cm. Further, the drone character varies as per ecological conditions, species, genotype, and other environmental conditions.

The drone honey bee develops from unfertilized or fertilized eggs depending on the homozygosity of the sex alleles in inherited genomic content. In the honey bee colony, if the polyandrous queen honey bee mates with the drone honey bees of the neighbouring colonies, then the drones develop from the unfertilized eggs, confirming the haploid parthenogenesis. However, the mating of the queen with the drones of the same colony accelerates the feasibility of the development of drones, even from fertilized eggs. In the above-mentioned former case, the drones are known as the haploid drones, whereas in the latter case, the drones are referred to as the diploid drones. Generally, the diploid drones are removed by worker honey bees by recognizing the pheromones coated on the egg surface. The worker honey bees can remarkably distinguish the queen's drone eggs and the workers acting as pseudo-queens’ drone eggs. The pseudo-queen develops if the colony is queen-less or the queen is not carrying the required reproductive potential and pheromonal emission. Drone development takes 24-25 days in total, with four distinct phases: egg, larval, pupal, and adult, with durations of 3 days, six days, 15-16 days, and about 1-3 months, respectively. The present chapter is attributed to the drone honey bees' developmental synchronicity, haploid inheritance, parthenogenesis, and patrilineal genomic contribution to the colony that influences colonial behaviour, productivity, life span, immunity, and others.

The drone honey bee produces volatile chemicals during developmental and adult stages that facilitate chemical interaction between drone larvae and workers, drone to drone, and drone to the queen. For example, the drone larvae solicit larval food from nurse bees through chemical messengers; further, adult drones attract other drones to drone congregation areas (DCA) through pheromones; the drones attract queen honey bees to DCA through volatile chemicals. The mandibular drone gland secretes volatile chemicals, a mixture of saturated, unsaturated, and methyl-branched fatty acids. In the drone honey bee of Apis mellifera, about 18,600 olfactory poreplate sensilla per antenna are associated with receptor neurons. The current chapter highlights the role of chemical volatiles in Drone honey bee’s life and overall influence.

Mating in honey bees occurs in the drone congeration area, where the queen and drones gather for reproduction. Sexually mature drones from all colonies congregate there, and the queen mates with multiple drones, increasing patrilinear inheritance variation. The variation in genomic content results in specific colonial behaviour, productivity, and strength. The current chapter discusses mating in honey bee colonies.

A few protocols are available for artificial drone rearing under controlled conditions within or outside the honey bee colony. The initial development phase of the drone development can be completed on royal jelly exclusively. Still, on worker jelly, complete drop development can be carried out, as witnessed by a few researchers. Sugars accelerate the drone's growth and support the passage of the drone through certain embryonic and post-embryonic stages. The drones contribute patrilineal genomic content that influences the overall strength of the colony, colonial behaviour, productivity, and other characteristics. The current chapter is attributed to some available artificial haploid/diploid drone-rearing methods and the influence of multiple patrilineal genomic content contributions to other honey bees