Authors: Philip A. Moore, Michael E. Wilson, John A. Skinner
Department of Entomology and Plant Pathology, The University of Tennessee, Knoxville TN
Department of Entomology and Plant Pathology, The University of Tennessee, Knoxville TN
Honey bees (Apis mellifera) are highly social insects and the colony organization is divided into separate castes that allow for division of labor and specialization in particular tasks. The honey bee queen is the sole reproductive female in the colony and she specializes in egg laying, while the remaining female “workers” perform all other colony duties and the male “drones'” only function is to mate with a virgin queen. The quality of the queen, often associated with her reproductive ability, can have profound impact on a colony’s honey production, disease prevalence, and overwintering ability. Queen failure is consistently listed as a cause of colony mortality in recent winter loss surveys (vanEnglesdorp et al 2010). Therefore maintaining high quality queens is essential for every beekeeping operation.
The biology of honey bee queens is a well researched field and many interesting facets of the honey bee life cycle are determined by the queen and the pheromones she produces. In the life cycle of honey bees, a worker and a queen are identical when in the egg and young larva stages. The difference between the two comes about through the feeding of the larva. Food is provisioned in to the cells of developing larvae by adult worker bees that secrete brood jelly from their mandibular glands after ingesting pollen, nectar, and bee bread. Queens are raised entirely on royal jelly, while workers are fed various combinations of larval jelly, pollen, and nectar. This diet influences the level of juvenile hormone produced by larvae and by the third day of larval development, the resulting caste of the adult is established based on the hormone level. The especially rich diet of larval queens allow them to develop very quickly, from egg to adult in about 16 days, while workers develop in about 21 days. The queen also develops into a larger adult form and the cell she pupates in must accommodate this size. Therefore an enlarged (conical shaped) queen cell is formed for the egg to be laid in, or developed around an existing egg in a worker cell. To learn more about queen cell development and worker differentiation.
After a new queen emerges, her development is not yet complete; she must mate with multiple drones, store their sperm, and initiate egg laying to become fully developed. Queens typically mate in the 5 or 6 days after emergence (Tarpy et al 2004). Until this point, workers pay her little attention, but once she is ready to mate, the workers form a court around her (Figure 1). Once she departs, the workers will help her find the colony by producing a Nasonov pheromone at the hive entrance. The queen will take 1-2 orientation and 1-5 mating flights in mid-afternoon on calm, sunny days over the course of 2-4 days.
Figure 1: Queen and her court. Credit: The Food and Environment Research Agency (Fera), Crown Copyright
Mating occurs at drone congregation areas, of which there are usually many within flying distance (2-3 km) from the apiary. Once the queen flies through a congregation area, drones quickly orient to her using visual and chemical cues (Gary 1962). The drones form a “drone comet” behind the queen, which is a swarm like formation. The drones approach until one is able to mount and explode its semen into the genital orifice of the queen in a rapid fashion lasting only a few seconds. The drone becomes paralyzed, flips backwards, and propels the semen through the queen’s sting chamber into the oviduct. The drone dies within minutes or hours of mating. She will mate with 7-17 drones during the mating period (Adams et al 1977) typically in quick succession before returning to the colony and storing the millions of sperm in her spermatheca. After mating, many physiological and behavior changes occur as her ovaries complete maturation and eggs become vitellogenic (Tanaka and Hartfelder 2004).
The genetic diversity of the colony resulting from mating with multiple drones results in higher colony productivity, reduced brood diseases, and ultimately greater colony survival (Tarpy and Pettis 2013; Tarpy and Seeley 2006; Seeley and Tarpy 2007; Palmer and Oldroyd 2003). The majority (83%) of benefits realized from mating with multiple drones is achieved with 7 mates (Tarpy and Pettis 2013). Most commercially produced queens exhibit high (> 7 mates) mating frequency (Delaney et al 2010; Tarpy et al 2012). Drone production increases in the spring prior to queen production, ensuring adequate drone numbers for most apiaries. Queen producers must ensure adequate and healthy drone populations in their own or neighboring colonies. Weather is also an important consideration for queen mating and may greatly impact a virgin’s ability to optimally mate and return to her colony. Virgin queens typically mate within 2 weeks (Oetrel 1940) and if weather conditions do not allow for mating, they may start laying unfertilized eggs after 3 weeks (Conner 2008).
Queen Function in a Colony
Once the queen has mated her two ovaries swell with 150-180 egg producing ovarioles (Winston 1991). These ovarioles produce an unlimited number of eggs, up to or exceeding one million eggs, while the spermatheca holds up to seven million stored sperm that the queen will use to fertilize her eggs over a lifetime. It generally takes 2-4 years for all the sperm to be used at which point, the queen ceases to produced fertilized eggs and the colony will supersede her (Winston 1991). A queen will commonly lay 1,500 eggs in a single day, while the actual number will vary based on seasonality, number of adult workers, availability of open cells, disease or pest prevalence, and abundance of pollen or nectar. The queen rarely, if ever, feeds herself. The amount the queen is fed by adult workers in her court (Figure 1) is related to the queen’s egg laying rate. As the colony grows, the egg laying rate increases, and the queen is fed more often and for a longer duration (Chauvin 1956, Allen 1960).
Figure 2: Healthy brood with a good laying pattern. Credit: The Food and Environment Research Agency (Fera), Crown Copyright
The queen produces numerous pheromones that inhibit or stimulate specific actions in the worker caste. The full extent of pheromone use is yet to be understood, but we know queen produced mandibular pheromones inhibit queen rearing and swarming (Melathopoulos et al 1996), attract drones for mating (Gary 1962), induce workers’ pollen foraging and brood rearing (Higo et al 1992), increase nectar foraging (Gary 1962), and prevent worker ovary development (Butler and Fairey 1963). The amount of these pheromones produced and released by queens is dependent on queen age, mating status, time of day, and season (Plettner et al 1997; Richard et al 2007).
Assessing Brood Patterns
One primary way of determining the quality of a laying queen is to examine the pattern of eggs and developing brood in the frames of a colony. Inspecting brood frames should be done on a regular basis during routine colony inspections. A high quality queen will exhibit a consistent and abundant pattern of brood. Concentric circles of like aged brood should be observed in a tight pattern with few skipped cells with the oldest brood in the interior and younger brood in similar stages radiating outward (Figure 2). On the periphery of the brood, pollen or bee bread is typically stored with honey or nectar often found on the outside edge of the frame. Finding a frame with capped brood from edge to edge is common during most of the season (Figure 3).
Figure 3: An excellent capped brood frame. Credit: The Food and Environment Research Agency (Fera), Crown Copyright
The number of brood frames present in a colony will vary, but associating how much brood should be expected during specific seasons will help the beekeeper understand if too little brood is being produced, which is limiting colony expansion. Figure 4 illustrates a generalized rate of adult bees and brood produced by month for colonies in the US, although this will vary greatly with different geographical locations and management practices. During the spring build up period, producing large numbers of adult bees is essential in order to take advantage of the nectar flow and honey production period.
Figure 4: Pattern of adult population and brood production by season. Credit: Mid-Atlantic Apiculture Research & Extension Consortium
Little brood is produced in the winter months, but when the first forage becomes available and weather allows exiting of the colony to collect pollen, brood production will rapidly expand. As new brood is produced, overwintering bees will be replaced and it is essential for these replacement bees to be healthy and abundant. Inspect colonies early in the season when the temperature is about 55° F or higher, while bees are entering and exiting. Check for brood production and ensure the queen has plenty of space to lay and workers have sufficient food reserves left over to raise new brood. Supplemental sugar water (Figure 5) or pollen patties may be provided if stored food is limited, or natural forage is scarce. Any deviation from abundant, healthy looking brood (pearly white larvae, non-punctured or removed capping of pupae) may indicate a serious problem that will ultimately affect the ability of the colony to build up, produce honey, and survive through the summer.
Figure 5: Feeding sugar water in a hive top feeder. Credit: The Food and Environment Research Agency (Fera), Crown Copyright
Queens can die suddenly for a variety of reasons, most commonly disease, predator attack, or beekeeper error. When a colony loses its queen, even the best case can result in a severe setback in colony growth and productivity. In a worse situation, workers will not succeed in rearing a replacement. A colony without a queen for a protracted period will not survive. Detecting when a colony has lost its queen is important since a beekeeper can remedy the situation when steps are taken in a timely and appropriate manner.
Worker behavior changes dramatically after becoming aware that the queen is no longer present, which they detect through mandibular pheromones (Melathopoulos et al 1996). Workers become agitated or aggressive and a “roaring” sound can be heard when first opening the queenless colony (Fell and Morse 1984). If brood is present, workers will begin queen cell construction, called “emergency queen cells”, over eggs or larvae and initiate feeding for this brood to be reared as queens (Fell and Morse 1984). Workers may also move brood into existing empty queen cells cups (Butler 1957, Punnett and Winston 1983). Most queen cells are produced within the first 2 days after queen loss, and a colony will attempt to produce an average of 20 queens (Fell and Morse 1984). Priority is given to producing these queens and about 12-15 will survive to adulthood, while mortality of non-queen brood jumps to 40-50% (Winston 1992).
Emerged queens will mate, swarm, or attempt to kill other virgin queens. Swarming behavior after queen loss can be common and the causes are not well understood. One theory is that if the reason for queen loss is expected to recur, it may benefit the swarm to colonize a new location. Eventually, one queen will kill the remaining queens, mate, and begin egg laying. The process from queen loss to egg laying takes about 29 days (Winston 1991). During this period, new brood production stops and the adult colony population declines. The colony may become stressed and susceptible to pests or diseases. Colonies that are successful in rearing a virgin queen may still not rebound if the queen fails to mate or initiate egg laying. Introducing a mated purchased queen immediately after queen loss is detected may prevent negative symptoms from occurring. A colony in the process of rearing new queens that have a mating queen introduced may destroy the queen cells and accept the introduced queen, or they may reject the mated queen in favor of the queens they are raising.
Protracted Queen Loss
A colony which loses its queen without brood or is unsuccessful in producing a new queen will lead to laying workers (Figure 6). Many workers in a queenright colony have the potential to lay eggs, but the presence of queen pheromones inhibit ovary and mandibular gland development (Costa-Leonardo 1985). Workers will generally start laying 23-30 days after queen loss and unlike normal queens, will lay multiple eggs per cell (Figure 6a). Laying worker colonies generally do not accept new queens and aggressiveness between laying workers is common (Sakagami 1954). Since workers do not mate, these colonies only produce drone brood (Figure 6b) and will eventually collapse. Beware, laying worker colonies may form queen cells around drone larvae that will not produce a new queen. Once laying workers are established, no fertilized eggs are laid and therefore no queens are produced.
Figure 6: (a) multiple eggs per cell; (b) bullet shaped drone pupa, each may indicate laying workers. Credit: Zach Huang
Beekeepers should routinely inspect brood area for presence of eggs, especially if the colony exhibits symptoms of queenlessness. Observing eggs is an acquired skill and requires the beekeeper to orient himself with his/her back towards the sun. The frame is held at an angle allowing the light of the sun to illuminate into the cell, while the beekeeper looks downward into the cells. Eggs are similar in appearance to small grains of rice and only one per cell should be present if laid by a queen. Occasionally young queens or abnormal queens will lay multiple eggs per cell, but not as many or as haphazard as seen in laying worker colonies. Laying workers may also lay eggs in pollen cells and on the side wall of cells.
Generally, queenright colonies should contain eggs at all times of year. Exceptions are at times of nectar or pollen dearth which often occurs in summer and winter. If eggs are not found, and queenlessness is suspected, the youngest stage of developing bees that are present indicate how long the colony has been queenless. Check for queen cells and be especially careful to avoid damaging queen cells when inspecting frames. A colony without eggs or queen cells may be induced into producing a new queen by adding a frame of eggs or young larvae into the brood area from another colony. Alternatively, a purchased queen can be introduced.
If the colony has progressed into a laying worker stage, practically speaking, little can be done to save the colony. Combs from colonies with laying workers can be salvaged and utilized in other colonies. The adults are often shaken off first. These workers may fly into an adjacent colony, which if queenright and healthy, will not turn into another laying worker colony because of the introduced workers. However, movement of combs and bees into other colonies can spread diseases, if present. Due to difficulty in dealing with laying worker hives, early diagnosis of queenlessness is essential.
Swarming is a form of colony reproduction where new virgin queens are produced and the old queen departs from the colony with a large portion of adult bees to find and establish a new colony. Factors involved in swarming include colony size, brood nest congestion, worker age distribution, and a reduced transmission of queen pheromones throughout the colony. Once a colony becomes crowded, distribution of queen pheromones, which prevent workers from producing new queens, diminishes and swarm behavior initiates. Swarming behavior may result in a single large swarm or subsequent afterswarms that contain virgin queens and a relatively small number of adult workers.
Figure 7: (a) a large swarm of bees on a tree branch; (b) immature queen cell cups. Credit: Zach Huang
The first sign of pre-swarm behavior is the appearance of new queen cell cups (Figure 7b). Queen cell cups can be found throughout the season, but the number of cups increases in spring, prior to queen rearing. Swarming will not commence until queen rearing is initiated. These queen cells are also called “swarm cells”. Workers will destroy some of the swarm cells that they initiate, typically those reared from older larvae (Hatch et al 1999). An average of 15-25 queen cells will be sealed prior to and after swarming. Colonies usually swarm the first day of queen cell capping or the following day, 8-10 days after queen rearing is initiated.
About a week after the initial swarm, virgin queens begin to emerge. Virgin queens will either produce an afterswarm or fight each other until one remains, mates, and initiates egg laying (Visscher 1993). The presence of a virgin queen in a colony may suppress the emergence of other queens. A virgin queen announces her presence through “piping”, a high pitched sound produced by pressing the thorax against the comb and operating her wing muscles, without spreading the wings (Simpson and Cherry 1969). The entire swarming process from queen rearing initiation to a new laying queen takes about 4 weeks. It will be another three weeks until the first offspring of the new queen emerges. During this time, new brood production slows and colony population declines (Tarpy et al 2000).
Since swarming typically occurs at the height of nectar production, an untimely swarm will dramatically cut honey production. Beekeepers intent on swarm prevention may remove uncapped queen cells to delay swarming, but the presence of capped queen cells indicate swarming is imminent or has already occurred. Therefore retaining capped queen cells is recommended to replace the swarmed queen.
Splitting a colony prior to swarming, termed an “artificial swarm”, may reduce the urge of bees to perform swarming behavior. Swarm queen cells are often produced near the bottom bars of brood frames. A quick check for swarm cells can be accomplished by lifting the front end of the top brood box, propped against the rear end of the bottom brood box (forming a 90 degree angle), allowing inspection of all the bottom bars in the top brood box. Queen cells with royal jelly present, indicate they have developing queens and swarming is approaching. Beekeepers should check at least every two weeks in the spring for swarm cells to know when to make divides and prevent swarming. Ensuring adequate space for egg laying and food storage, especially during the nectar flow period, by adding supers with empty frames of comb, is essential to preventing swarming. Depending on the productivity and amount of adult bees in a colony, honey supers may need to be added every 1-2 weeks in some areas, during nectar flow.
Another form of queen reproduction is supersedure, when the old queen is replaced. Colonies led by old queens with low fecundity show significantly reduced honey production (Nelson and Smirl 1977). High quality queens produce colonies that grow larger, build more comb, and store more honey and pollen comparatively (Rangel et al 2013). The causes of supersedure are not well understood but a few factors likely contribute, such as: reduced presence of queen pheromones, an injured or diseased queen, laying unfertilized eggs or insufficient quantities of fertilized eggs, and age differences in pheromone production.
Some beekeepers will “requeen” colonies annually to take advantage of young queen qualities, especially if swarming is prevented. Requeening is simply an “artificial supersedure”, a process where the beekeeper locates and removes the existing queen and replaces her with a new queen, typically a purchased, mated queen. If problems associated with the existing queen are detected, it may be beneficial to requeen.
Recommendations should be followed when introducing new queens to prevent the new queen from being killed by the workers in the colony. Before introducing a new queen, a colony should be left queenless for 24 hours to allow the former queen’s pheromones to dissipate and help ensure acceptance of the new queen. New queens are introduced in cages with a candy at one end (Figure 8). The bees consume the candy over time and allow the pheromones of the new queen and colony members to integrate before the workers can fully access the queen. Once the candy is consumed, the queen is released from the cage and is typically accepted. However, queens should remain in their cage for 3 days before release, by adding a cork or other blockage over the candy end. A strong colony can consume all the candy in a few hours which will release the queen too quickly. The cork protecting the candy is removed later on strong colonies, and sooner or not used at all in small colonies. A queen introduced without a slow release process may be killed by the colony.
A queen introduced in a cage that is not released after 72 hours should be freed by the beekeeper, unless it is clear they have not accepted the new queen. Once accepted, the beekeeper may need to inspect the colony every 7 days to remove supersedure cells until the colony stops building them, if the beekeeper wants to ensure the new queen is not replaced. If a supersedure is acceptable, this step can be skipped. Smaller colonies are more likely to accept a replacement queen than larger colonies.
Figure 8: Inserting a queen into a mailing cage, also used for queen introduction. Credit: The Food and Environment Research Agency (Fera), Crown Copyright
Queen Rearing and Bee Breeding
Introduced queens are either acquired from commercial queen producers or can be reared by the beekeeper within the same apiary. The US beekeeping industry is based upon large-scale queen and package bee production concentrated in California, Hawaii, and the southeastern US. Although the terms queen rearing (the propagation of queens) and bee breeding (evaluation and selection of breeding stock) have traditionally been used interchangeable in the beekeeping community, these represent two different enterprises. Queen producers are typically family businesses, with high overhead, high demand, and lack expensive breeding programs. These operations range in size from between 5,000 to 150,000 queens produced annually and in total provide about one million queens to the 2.4 million colonies nationwide (Cobey et al 2012).
Commercial breeding stock in the US is selected from among the thousands of colonies in commercial apiaries that exhibit desirable characteristics such as: large population, quick spring buildup, egg laying pattern, temperament, color, weight gain rate, overwintering ability, and limited disease and pest prevalence. Queen producers may augment their programs with specialty breeding stock (like resistant or hygienic strains) from the USDA and increased interest in “survivor stock” or “locally adapted stock” continues to shape consumer preferences.
For the experienced beekeeper, queen rearing is an exciting and worthwhile endeavor. Various methods are used to produce queens and all rely on the natural swarming impulse and queen replacement cycle of honey bees. Many books, kits, and training classes are available on the subject. Queen rearing is most easily accomplished in the spring when nectar and pollen is abundant and colony populations are at a peak.
Diseases and Pests of Queens
Because of the rapid development time and infrequent availability, many honey bee parasites and pathogens either do not or cannot infect queens. A recent survey of 124 commercially produced queens from 12 US producers showed that the overall disease and pest prevalence in queens is low and mating quality high (Delaney et al 2010). Nosema apis infection in honey bee queens may affect the development of eggs and even stop reproduction (Liu, 1992), but the pathogen is not transmitted through the eggs to the offspring (Webster et al. 2008). No appreciable Nosema spores were found in US queen producers (Delaney et al 2010). For more on Nosema disease.
Unlike Nosema, many honey bee viruses are transmittable from queen to egg, although this usually causes a less severe infection without detectable symptoms. The Delaney et al (2010) survey detected all seven viruses analyzed in US produced queens, with Deformed Wing Virus (DWV), a virus that is transmittable from queen to egg (Chen et al. 2004) being very common, while other viruses were much less common. For more on honey bee viruses, In the same survey, Tracheal mites (Acarapis woodi) were only found in queens from one source, indicating control of this pest is successful in commercial operations.
The quality of a queen has historically been determined by morphological measurements like weight and width of her thorax or head. These factors are still considered important today because they represent some of the factors influencing fecundity, although they are relatively less reliable indicators. Because the queen is responsible for laying fertilized eggs, an important factor influencing queen quality is how well she is mated. The number of stored sperm and number of drone donors strongly influences the reproductive output of a queen over her lifetime. Disease and pest prevalence are also important factors because these can limit reproductive output or be transmitted through sperm or egg to the offspring.
Assessment of mating quality, morphometry, and disease presence in queens is now offered with a fee for service model from the NC State Queen & Disease Clinic through the Bee Informed Partnership (BIP). This clinic will grade queens using a simple letter designation (A-F) and describe the factors affecting the sample queen and what may influence those factors. For more information on queen quality screening
The health and productivity of a honey bee colony is directly influenced by its queen. Honey bee workers can sense when a queen is failing and will act to replace her, but this process is slow, precarious, and may ultimately be unsuccessful. Therefore it is important for the beekeeper to recognize when a queen is performing optimally and when factors like disease and pest pressure are limiting brood production. Requeening may be effective in alleviating some of these problems. Experienced beekeepers can produce their own queens, while most beekeepers will choose to purchase queens. An informed beekeeper will inquire as to the health and productivity of queens prior to purchase and as queen evaluation tools become more practical and inexpensive, queen producers should independently evaluate their products.
Adams, J., Rothman, E. D., Kerr, W. E., & Paulino, Z. L. 1977. Estimation of the number of sex alleles and queen matings from diploid male frequencies in a population of Apis mellifera. Genetics, 86(3), 583-596.
Allen, M. D. 1955. Observations of honey bees attending their queen. Brit. J. of Anim. Behav. 3: 66-69.
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