Biology of the Honey Bee
Contributed by Gigi Davidson, BSPharm, DICVP
Since a single colony can contain 30,000 to 60,000 honey bees, knowing how to recognize the life stage, role, and responsibilities of each individual bee is of great value in evaluating the health and strength of a colony. Strong colonies must have healthy queens and adequate populations of adults and brood in various stages of growth. Veterinarians caring for bees should be able to inspect a colony and evaluate the vitality of the colony based on signs of organized and sustained reproduction. Learning to discern workers from drones from queens in all adult and pupal stages can be daunting. Veterinarians wishing to practice this skill before visiting actual colonies can benefit from online interactive games that test the ability to properly identify colony members and life stages.
Since a single colony can contain 30,000 to 60,000 honey bees, knowing how to recognize the life stage, role, and responsibilities of each individual bee is of great value in evaluating the health and strength of a colony. Strong colonies must have healthy queens and adequate populations of adults and brood in various stages of growth. Veterinarians caring for bees should be able to inspect a colony and evaluate the vitality of the colony based on signs of organized and sustained reproduction. Learning to discern workers from drones from queens in all adult and pupal stages can be daunting. Veterinarians wishing to practice this skill before visiting actual colonies can benefit from online interactive games that test the ability to properly identify colony members and life stages.
The table below describes brood development in days and cell appearance.
Worker BeesA large majority of the bees in a colony at any given time are worker bees. These infertile females are the life force of the colony and perform all necessary tasks, except reproduction. They are the smallest bees in the colony, have a 21-day development period from egg to emergence, and have the shortest life span: 4-5 weeks in the summer and as long as several months in the winter.
Worker bees start their jobs as soon as they emerge from their cocoons and are responsible for cleaning their birth cells thoroughly so that they are ready for the queen to lay another egg. Although full size at emergence, because the worker’s muscles and glands are not developed enough to perform certain tasks, she starts as a house bee. Tasks include cleaning brood cells and attending the queen (feeding and grooming her), progressing to feeding brood, packing cells with pollen, building comb, removing dead bees from the colony, receiving and processing nectar, and guarding the front entrance of the colony. Once she has learned how to orient herself to the sun, she becomes a field bee with a job of foraging for food and water. It is necessary to mention that each worker bee will perform any task that she is capable of at the time. For example, if she is bringing nectar into the colony and notices that the body of a dead bee or larva needs to be removed, she will do it on her way back out to forage. Eventually the long and difficult work of foraging takes a toll on the wings of field bees, causing them to no longer be able to fly while carrying a load. At this point the worker can no longer contribute to the success of the colony, so either her sisters will not let her back into the colony or she will die. Though worker bees are capable of laying eggs, these eggs are usually infertile. However, if the colony becomes queen-less and there are no pre-designated queen brood eggs , the ovaries of some workers will become active and they will begin laying eggs. The eggs laid by workers may be detected by their numbers (multiple eggs in one cell) and by their placement on the sides of the cell (their abdomens are shorter than the queen’s and they cannot reach the center bottom of the cell where the single egg should be deposited). This situation is called “laying workers” and it is a sign that the colony is on the verge of failing. Drone Bees
Although often maligned as lazy superfluous takers from the hive, the male drone bees are not only essential to the propagation of the hive, but they are also the sense organs of the colony. They are larger, plumper, stingless, with significantly larger eyes and antennae than workers or queens. The gestation of a drone is 24 days from egg to emergence and is often longer than his lifespan, which may only be a few weeks.
Drones are permitted by guard bees to freely enter any other colony since they are not aggressive and never rob honey stores from other hives. They are known best for their role in flying up to drone congregation zones to mate with virgin queens to ensure that all her eggs will be fertile. Although some references indicate that drones never leave the colony except to mate a queen, this author has observed drones freely flying back and forth between colonies throughout the spring, summer, and early fall. One can speculate that these drones communicate important information about neighboring hives. If successful in mating with a queen, he will die abruptly in the air. If he survives until winter, his sister workers will kick him out of the hive (because he cannot perform any hive chores) and he will die of exposure or starvation. Since the drone is the longest to pupate, varroa mites preferentially lay their eggs in drone cells. Many beekeepers take advantage of this and remove all drone brood as soon as the cells are capped. While this may temporarily reduce mite load, the long-term effects of significant reductions in drone populations may be more adverse than good in terms of colony vitality. |
Queen BeesAs much as the workers are the life force of the colony, the queen is the most important bee in the colony. Her ability to lay fertile eggs and to rally the entire colony around her individual pheromone (scent) is the difference between survival and collapse of an individual colony. The queen is the largest bee in a colony and her life span is typically in years instead of weeks; 2-3 years is average but with good husbandry and forage a queen can be productive for 4-5 years. Queen development is ironically the shortest of the bees with emergence from the cocoon at 16 days.
Once the beekeeper’s eye is trained, queens are easily spotted by their long slender abdomen that tapers to a more defined point than other bees and extends far past the end of her wings, and usually is of one color with no bands. The queen has no pollen baskets on her legs and lacks wax glands because she will never have to perform these tasks. Because it can be difficult to find the one queen in a colony of 60,000 bees, queens are often marked with a dot of colored paint on the back of the thorax to identify the age of the queen via an internationally-controlled coloring system (see the table below for the coloring system designations). Developing queens are easily recognizable from those of other bees as their cells are vertical in orientation with a mottled outside appearance that resembles a peanut shell, located on the bottom of the frames of comb. Queens are fed solely royal jelly for their entire development, which provides a distinct nutritional advantage over the other bees. When queens emerge from their cell, they often must fight other emerged queens to the death in order to remain the sole queen. Within a few days of establishing their sovereignty, they fly off to be mated with multiple drones then return to the colony to begin a lifetime of egg laying. Semen collected on the mating flights (typically 1-3 flights mating with 10-20 drones per flight) is stored in the spermatheca and is used to fertilize eggs. Fertilized eggs will develop into worker bees, while non-fertilized eggs will develop into drones. It is actually the workers that determine how many drones are needed and indicate this to the queen by building larger cells on the periphery of the comb. Similarly, the workers will create multiple queen cells (known as swarm cells) on an annual basis, within which the queen will lay future queen eggs, one who will become her successor. Just before the young queens emerge, the old queen flies off with half of the workers (known as swarming) to seek a new nest site and leaving all the drawn comb, honey, and nectar stores and developing brood behind for the new queen. The new queens emerge, fight until only one remains, and the cycle continues as she begins her reign over the colony. Despite this being the natural reproduction cycle for a honey bee colony, beekeepers often try to thwart swarming because they do not wish to lose half of their bees in the peak of the nectar flow. However, swarming is the healthiest and most natural form of honey bee reproduction. Occasionally, a reigning queen will die before swarming or the workers will decide that she is not performing in a fashion that will ensure colony survival and that they must replace her. In this situation, workers will select an egg (three days old or less) in the center of the frame of come and build a vertical queen cell around it, then fill the cell (known as a supercedure cell or emergency queen) with royal jelly to allow this egg to become a queen. |
Honey Bee AnatomyIt is important for veterinarians to understand honey bee anatomy and physiology, particularly as they relate to signs of disease and may impact drug and pesticide disposition.
Honey bees are about 0.5 inches in length, and each part of their bodies is highly evolved in purpose. The brain is only about a cubic millimeter in size but contains the one of the densest collection of neurons and synapses for invertebrate species. The honey bee has 5 eyes: 2 larger compound eyes covered with thousands of lenses called ommatidia that allow 360° vision, and 3 smaller eyes called ocelli that perceive light into the UV spectrum helping them see and locate pollen. Just behind the eyes lies the hypopharyngeal gland, which is responsible for producing royal jelly. Bees have 2 antennae with as many as 170 scent receptors. The antennae are used to determine air speed and orientation to the sun during flights, and the right antennae alone is used to communicate. Honey bees have a proboscis used to collect nectar into their honey stomachs, and strong mandibles used to chew, build wax comb, and open flowers to access nectar. The thorax (middle section of a honey bee) holds 2 pairs of wings and 3 pairs of legs. The wings can be connected by hooks called hamuli during flight, then unhooked and folded back at rest or when used to generate heat through shivering in the winter. Deformed wings are a sign of the deformed wing virus which is carried by varroa mites. All legs have taste receptors on the tips. The front pair of legs is used for cleaning antennae; on workers, the middle pair of legs is used for pushing pollen and propolis into the pollen baskets that are located on the rear pair of legs. Drones and queens do not have pollen baskets. The abdomen of workers contains digestive organs, wax glands, the venom pouch, and the honey crop. In addition to digestive organs, the abdomen of queens and drones contain reproductive organs. The queen’s abdomen contains ovaries that will start producing eggs when she is about 1-2 weeks old, as well as the spermatheca which holds semen from mating with drones on her mating flight. Once the drone has successfully mated with a queen, his phallus is torn from his abdomen and he dies. Underneath the abdomen of workers are wax glands. Young workers can secrete 8 scales of wax in 12 hours (for reference, it takes approximately 1000 scales to build one gram of comb). At the end of the abdomen in workers and queens is the stinger. The worker’s stinger is barbed and will be stuck in the tissue of stinging victims, thus eviscerating and killing the worker when she pulls away after stinging. In contrast, the queen’s stinger is not barbed, thus she may sting multiple times, although queen stings are rare. |
Basic Honey Bee Physiology Related to Drug Disposition
Honey bees lack a liver or kidneys—instead they utilize Malpighian tubules to drain the midgut of nitrogenous waste as uric acid. The Malpighian tubules also help maintain osmotic equilibrium of the hemolymph.
The principal drug metabolizing enzymes for honey bees reside in the Malpighian tubules, fat body, midgut, mitochondria, and the cuticle (exoskeleton). The primary xenobiotic (drug) metabolizing enzymes are glutathione transferases, carboxylesterases, and cytochrome P450 monooxygenases. Interestingly, the honey bee genome encodes for only 46 CYP isoenzymes which is approximately 33-50% less than other insects.
The principal drug metabolizing enzymes for honey bees reside in the Malpighian tubules, fat body, midgut, mitochondria, and the cuticle (exoskeleton). The primary xenobiotic (drug) metabolizing enzymes are glutathione transferases, carboxylesterases, and cytochrome P450 monooxygenases. Interestingly, the honey bee genome encodes for only 46 CYP isoenzymes which is approximately 33-50% less than other insects.