Selection and reproduction

by Giacomo Acerbi

The other half of the sky. Sperm with wings… Underestimated… unknown…

Drones play a crucial role for well-being, performance, survival, reproduction of the hive super organism: well-bred males, in full reproductive health, of robust and vital offspring, are an essential component of the future of the colony.
A summary of the aspects that may or may not determine the health and quality of the drones, on the new important knowledge and on the recent pitfalls for this indispensable harmonious link of the complex life cycle of the hive

Humanity has been in mutual interaction with bees since the dawn of time, it has greatly and variously conditioned their life cycle and has spread their presence territorially, but in thousands and thousands of years of bees and their life cycle man has understood little or nothing! On the other hand, the understanding of the “wonders and mysteries” of nature is in our history progressed more easily on perceptible phenomena, better if with the naked eye. Very little man for millennia has been able to understand the invisible, the multiple, indispensable vital forms that are too minute to be observable.
The bees then, in addition to being small and with a life cycle hidden in their constituent nest, are, among all the living species bred, one of the most distant, different and “other” from us humans. When the invention of the removable and observable honeycomb allowed us to start – finally! – to understand something we have (with the usual presumption!) considered to have understood everything! But those simplistic initials and primitive “explanations” of basic phenomena have far from opened the casket of the mysteries of the hive. How many of us have been trained on manuals that propagated the “scientific truth” that the colony would be governed by the queen’s pheromone alone?
Strangely enough, then, despite the fact that almost all human civilizations have hinged on the rigid subordination of woman to man, with bees on the contrary: the male bee has been assigned value only in relation to the queen and the reproductive act. An image of substantial uselessness has even been built and transmitted of the kelp, with even the development of practices, procedures and tools of “modern beekeeping technique” to contrast various deposition, breeding, if not even survival in the hive.

Instead, I propose that the drone be considered well-otherwise: an indispensable and determining link in the life cycle of the colony.

Pagine di

Pages from “Bee-Master to Charles II”. Book printed in 1679 by Moses Rusden, which includes extensive descriptions of the bee colony, proposed as an example of perfect monarchy in harmony with its “King”, and related homage to Charles II. Only since the nineteenth century has the notion spread that the colony would be governed by a female, and this both for the Enlightenment impulse to observation, and thanks to the new ability to make larger glass sheets, essential to be able to make observation hives

Illustration Ukraine of the early nineteenth century

Ukrainian illustration of the early nineteenth century. Since the dawn of time humanity has greatly and variously conditioned the life cycle of bees, but in thousands and thousands of years man on the hidden and secret life of the hive has understood little or nothing!

The kelp has, in fact, equal if not greater importance than the female component both as an element of fundamental quality (as a reproducer) for the well-being and performance of the hive, and from a genetic point of view, and finally selective: a super organism with complex genetic characteristics, particular, and clearly “in itself” compared to most of the many living species, in which, for example, the relationships of kinship between the different subfamilies of workers of the colony are determined by the male sperm sample with which the queen has fertilized her eggs. Not a single male (bull, stallion or boar) but a number ranging from 6 to 25 drones (15 on average) determine the genetic inheritance of a colony. Inrecent years a serious trend of loss of longevity and fertility of queens has intensified, increasingly “habitual” and repeated substitutions, reduction of fertility, which often result in lack of fitness (1) and performance of the entire colony, resulting in heavy additional costs for the breeder. And what have we beekeepers done? Much has been said and tried to improve about this problematic, but attention has been focused on the queen alone, starting from her biology and reproductive behavior, up to the manipulation by the beekeeper. We are there focused on: quality or not of fertilization as a function of the spermatheca, adequate temperature and nutrition to promote the migration of spermatozoa through the oviducts, size of the fertilization nuclei, timing for the correct homeostasis (2), possible damage from manipulation, caging and transport.

And the drones, how much and how do they count in this recent and dramatic deterioration of the vitality and fecundity of bees?

Recent studies, confirmed by a wealth of experience in the field, show that the health of drones and their reproductive value (3), the quality and viability of their sperm, they are decisive for the physiology, efficiency and longevity of queen bees, with important consequences for the set of performance of the entire colony.
There are many factors that can affect the reproductive quality of drones: causes of an environmental nature (nutrition,
temperature, seasonal trend), exposure to contamination, pathologies, genetics of origin, age, conduction beekeeping. In this regard, the new scientific acquisitions are remarkable and varied. Excellently highlighted, systematized and framed in an overview by the review study of scientific research on these issues by Rangel and Fisher, published by Apidologie in 2019. Study from which below I draw, synthesize and comment various and very interesting new knowledge and solicitations to deepen.

Beehive

In recent years, a serious trend of loss of longevity and fertility of queens has intensified, increasingly “habitual” and repeated replacements, reduction of fecundity, which frequently translate into the lack of fitness and performance of the entire colony, with consequent and heavy additional costs for the breeder | Photo by Giacomo Acerbi

The hive is a super organism with complex, particular genetic characteristics, and clearly “in itself” compared to most of the many living species. In which the kelp has equal if not greater importance than the female component both as an element of fundamental quality (as a reproducer) for the well-being and performance of the hive, and from a genetic point of view, and finally selective | Photo by Giacomo Acerbi

Queen Bees

They matter more than the act… the preliminaries!

The kelp has a development from egg laying to birth of about 24 days, this process can vary depending on the haplotype (4) ( DeGrandi, Hoffman 1998), temperature (Bienkowsha 2011) and general conditions of the colony (Winston 1987, Collison 2004) such as size, availability of food resources, etc …
Spermatogenesis, i.e. the process of sperm formation, begins during the larval phase (Bishop 1920) and ends in the pupal stage; sexual maturation is completed within the first week of birth, thanks to the migration of sperm into the seminal vesicles (Snodgrass 1956), with also the formation of two mucous glands that protect against pathogens and nourish sperm (Woyke 1983, Rhodes 2008). The viability and longevity of sperm are determined by the quality and composition of the proteins contained in the seminal fluid (Baer 2009, King 2011). Interestingly, the composition of these proteins is even related to the immuno-reaction to spores by Nosema apis del fuco ancora impupato (Grassi 2017).
The majority of defects of a morphological nature (size, weight, length of the wings) and of reproductive quality (number, motility (5) and viability of spermatozoa), are determined precisely in its prenatal phase.

In other words: the quality of the kelp is determined and plays mainly “under the operculum”

The kelp reaches sexual maturity around 6/8 days (Bishop 1920), but can reach 10/12 days (Woyke and Ruttner 1958) up to a maximum of 16 days from birth (Rhodes 2008). The first days of life the young males interact with the bees and are fed, warmed and cared for. It feeds only on honey or nectar both for trofallaxis, and by suggendolo directly, but only if the cells where the supply is stored are uncovered and within its reach. It participates from birth in the thermal control and ventilation of the colony thanks to an exceptional muscular apparatus.
The orientation flights of the young drone to identify the reference points and the exact location of the nest begin around the fifth / eighth day from birth (Galindo – Cardona 2015).

Ape nutrice all'opera

Nurse bee at work. The optimal breeding conditions are important because the quality of the kelp is determined and plays mainly under the operculum. For example, the process of sperm formation begins during the larval phase and ends in the pupal phase | Photo by Monica Rusconi

Having made the point of the position, its life cycle culminates with flights to the drone congregation area (DCA),, in which an average of 11,000 drones crowd in search of young virgins. It is not easy to identify a gathering area: the males make numerous flights of variable duration and frequency, and then dissolve the gathering after only a few minutes (Holm 2010). Strategic measure to prevent predators, such as bee-eaters, from discovering where to eat; especially since the high number of males reduces the risk of predation of virgin queens (Holm 2010). The kelp can ejaculate a volume of seminal fluid ranging from 0.91 to 1.7 microliters (Rousseau 2015) which contains 3.6 to 12 million sperm, all genetically identical (Collins, Pettis 2001).
Contrary to widespread beliefs and prejudices it is important to know that, although drones can fly at an average of 30 km/h (1 km in two minutes) and cover large distances (Holm 2010), they prefer to look for and establish the gathering areas (DCA) a few hundred meters from their hive / apiary of origin, to maximize the time of stay and the chances of fertilization (Koeniger 2005) and to maintain adequate vigor and viability of sperm.
The drone migrates, in fact, away from its hive of origin only for emergency situations (search for food and a family to welcome it) often determined by the stress of their colony, but almost all drones that cover long distances, are exposed to thermal stress, malnutrition, resulting in inadequacy to compete in a gathering area (DCA), where physical vigor and size are crucial to prevail in the fray (Berg 1997, Tarpy 2019).

 

Some factors that can compromise the reproductive health of the kelp

Hive cells

The availability of nutrition in non-operculated cells may be relevant for the well-being and survival of drones. That they feed only on honey or nectar both for trofallassi, and by suggendolo directly, but only if the cells where the supply is stored are unearned and within its reach | Photo by Giacomo Acerbi

Good continuity, quality and availability of the pollen supply of the hive, can affect the performance of the drones. The viability and longevity of sperm are determined by the quality and composition of the proteins contained in the seminal fluid | Photo by Giacomo Acerbi

 

Fuchi

It is complex to try to list and indicate in order of importance and priority the possible causes that can determine loss of male fecundity of bees. At the global level, I assume that hecatombs and fragility of hives caused by the almost ubiquitous spread of varroa and related diseases can be a determining and priority factor. But I have some reason to suppose that the specific context of environmental evolution of our country may have brought – even more than the varroa sickles – to the fore the set of environmental impacts. This hypothesis is based on the observation of the combination and contemporaneity of multiple factors, such as: progressive and incessant loss of availability of food resources (for example: drastic decrease in nectariferous exudations from rapeseed or sunflower; decrease in resources that can be spoiled by the impact of parasites – eucalyptus and chestnut etc …); constant increase in monocultures, combined with the highest spreading in Europe of biocides for “phytosanitary defense”, with relative and subtle consequences (for example on: corn, vine, hazel, fruiting etc …) and finally – precisely in order not to deprive us of anything – all seasoned with the particular exposure of our country to the increasingly frequent phenomena of climatic extremization, with the relative serious repercussions both on supply possibilities and on thermoregulation and health of bee colonies. Moreover, even the Italian people themselves are experiencing a serious and growing criticality for reproductive sterility, particularly male, with a worrying and peculiar increase, scientifically attributed above all to the overall interaction of the various environmental factors.

Temperature

Under optimal conditions, the drones are cared for and thermoregulated inside the hive at a constant temperature ranging from 33 to 35 degrees. The reproductive quality of males can be seriously compromised even by modest temperature variations, both in development and after birth.
For example, Jaycox (1961) observed how the sexual maturation of drones is compromised when bred at 31.1 degrees, while at 28.33 degrees their total sterility is determined.
Same drastic consequences for excess temperature: drones exposed even for a few minutes to a temperature of 40 degrees have a percentage of sperm mortality of more than 40% (Czekonska 2013).
In pupation, in which the complete formation of sperm takes place, the drones are extremely sensitive to small temperature changes: at 32 degrees they have larger testicles, more developed seminal vesicles and more expanded mucous glands than caring at a temperature of 35 degrees (Czekonska 2013). We can therefore if not glimpse, at least try to imagine the possible effect of sudden deaths and depopulation of hives, especially in spring, but also with extreme rise in summer temperatures. In fact, a sudden change and peak temperature outside the hive can totally compromise the quality of the drones, still pupated: they will be born, will be cared for by the bees and will mate with the queens but with very little fecundity and very poor results (little motility (5) and high sperm mortality), which will have an impact on reproductive value (3) and longevity of the queen and therefore on the performance of the colony.

Nutrition

Several scientific studies have confirmed the phenomenon we have been witnessing for years as a production sector: the incidence of the quality and quantity of food availability in the morphology, fecundity and quality of the drones. Czekonka (2015) tested how a forced deprivation of pollen with traps placed outside the hive during the larval period, determines a decrease in the size and weight of the kelp, a low volume of sperm and a difficulty in ejaculation in the adult male. On the other hand, Rousseau and Giovenazzo (2015) have ascertained how a supplementary nutrition with pollen substitutes and syrup in the spring period greatly affects the reproductive quality of the drones: larger male size, better sperm viability, increase in sperm count.

Biocyte contamination

The bibliography on the lethal and sub-lethal effects of exposure of bees to the various agroiocides is now remarkable for its size and results, but the scientific studies on the effects with respect to the reproductive quality of the male are very limited if not scarce. The little research available, which distinguishes between artificial conditions in which the drones are administered incremental doses of pesticide and situations of contamination in the field, highlight serious effects on: morphology, vitality and fertility rate of males. The family of neonicotinoids is the most studied – in particular: imidacloprid, thiamethoxam, clothianidin – and has demonstrated lethal effects on the reproductive capacity of drones, both if the molecules are administered, and if they are present in infinitesimal concentrations in the matrices (wax, honey, pollen) of the hive (Di Prisco 2013, Williams 2015, Straub 2016). It is also very interesting a study of exposure of males to the insecticide Fipronil (Straub 2016) which shows a clear correlation between the molecule and a strong increase in spores and aggressiveness in Nosema ceranae infection. This is the key to reflect on more: very often we find ourselves confronted with the pervasive influence of a multitude of residual molecules that, acting in a subtle and synergistic way with each other and with other co-causes (pathologies, scarcity of food resources, etc.), they can determine both mortality and the least recognizable, but perhaps even more serious, total senescence (6) of the drones.

Worldwide, hecatombi of hives and their relative fragility also from a reproductive point of view, are consequent to the almost ubiquitous spread of varroa and diseases related | Photo by Carlo Gatti

Fuco su alveare
Danni del glifosato

One of the many exemplary concretizations of glyphosate / agriculture, with a great tough face also defined and praised: “sustainable”. Serious repercussions on the health of bee colonies may result from reduced availability for supply. For the combination and contemporaneity of multiple factors, such as: progressive and incessant loss of plant biodiversity; Europe’s highest spreading of biocidal products; reduction of the possibility of grazing both spontaneously and above all from the cultivation of cultivars that no longer emit exudations indispensable to pollinators | Photo by Francesco Panella

Several scientific publications have shown how even the simple contamination of the nest wax with different acaricides (often in combination with each other) causes the drastic decrease in the egg laying of the queen and greatly reduces its attractiveness for bees (Rangel and Tarpy 2016).
Effects on the reproductive physiology of drones, the quantity of their sperm and their viability have been highlighted by the presence, both single and in combination, of acaricides. It is, in fact, more than worrying to note that also the bio accumulation of different acaricides in very low concentrations in the wax of the male honeycomb – amitraz, fluvalinate and coumaphos, as well as pesticides such as chlorpyrifos and chlorothalonil – determines very low viability of sperm, almost absence of motility (5) of spermatozoa, as well as their drastic numerical decline (Fisher and Rangel 2018). Moreover, a high amount of amitraz and its metabolites was also found in the wax of almost all the families examined, and numerous impairments of bee health were observed due to this bio-accumulation (Boncristiani 2012), namely: reduced fertility of the queen and low viability of spermatozoa in the spermatheca (Rangel and Tarpy 2016). On the other hand, organic acids are no exception: in addition to affecting the spermatogenesis of drones quantitatively and qualitatively, they also have an effect on the physiology of the adult male. Direct exposure to oxalic acid and formic acid (as well as thymol and eucalyptol) results in smaller drones, with reduced wing length and decreased sperm count (Shoukry 2013).

Breeding drones

Effects on the reproductive physiology of drones, the quantity of their sperm and their viability have been highlighted by the presence, both single and in combination, of acaricides. Even the bio accumulation of several acaricides in very low concentrations in the wax of the male honeycomb – of amitraz, fluvalinate and coumaphos, as well as pesticides such as chlorpyrifos and chlorothalonil – can determine very low sperm viability, as well as drastic decline in the number of sperm | Photo by Giacomo Acerbi

Breeding young drones

Breeding with young males. The age of the drones can affect: viscosity, volume, motility and viability of sperm. The seed becomes darker and more viscous the more advanced the age of the kelp: males who exceed 21 days of age have too high viscosity of the sperm with the consequent difficulty for the queens to expel the excess from the oviducts | Photo by Paola Bidin

Young drones

Drones in | breeding Photo by Paola Bidin

Battery of drones

Beautiful battery of males close to birth | Photo by Giacomo Acerbi

Diseases

A strong infestation of varroa under the operculum determines the birth of drones of reduced quality and less physical vigor: size lower than the norm (Hrassningg and Moritz 2010), reduced wing strength (Metz and Tarpy 2019) and consequent poor flight capacity (Slone 2012). The few males who manage to develop and be born from a cell infested with 20 mites, can manifest half of their normal body weight (Duay 2003). But also an infestation from one to six female varroes under the operculum, determines both in the development phase and at the emergence a considerable reduction in the weight and size of the male (Engels 2001). On the effects of viral load on the reproductive health of the male and on the vertical transmission of infections to the queen and offspring, there is a very limited bibliography. But recent studies have shown the presence of the viral genome of five different viruses (DWV, ABPV, BQCV, SBV, AmFV) in sperm ejaculated by apparently healthy drones (Titera 2019), with evidence of consequent venereal infection of queens inseminated with that sperm. But even more important and dangerous is the demonstration of transovarial transmission (7) of a strong viral load from infected sperm from drones to eggs laid by queens (Titera 2019). The trend of the colonies originating from these inseminated queens with infected sperm samples of viral load was also monitored and the symptomatic onset of pathogens such as sacco brood, the mortality of new queens in the real replacement cells (black cell) and, in general, loss of fitness were observed. (1) and apparently asymptomatic colony performance (Titera 2019).

Age

Many studies have shown that the age of drones can affect: viscosity (Cobey 2007), volume (Locke, Peng 1993), motility (5) and sperm viability (Locke, Peng 1993). The seed becomes darker and more viscous the more advanced the age of the kelp: males who exceed 21 days of age have too high viscosity of the sperm with the consequent difficulty for the queens to expel the excess from the oviducts (Czekonska 2013). Locke and Peng (1993) also showed how sperm motility (5) decreases by about 80% in drones over 20 days old.
Therefore mating with excessively “mature” males can result in a loss of longevity and poor performance of the queens. I hope with these first hints to have stimulated and solicited new: curiosity, attention and interest in “the other half of the sky” of the bee colony. I will return, I hope soon, to the same theme in terms of what the beekeeper, the breeder and the breeding queen bees can try to achieve for the improvement of the bee park. If we want to have healthy and productive bee colonies, long-lived and performing queens, we cannot continue to neglect the strengths and fragility of the drones, and therefore not invest a part of ours: commitment, effort and work for their health, breeding and selection. Thanks to adequate techniques of preparation of the colonies used as male lines, to the maintenance of the vitality and fecundity of the drones, to the genealogical selection it is possible to obtain more than interesting results in terms of fitness (1) of hives and try to implement a widespread, fast and ubiquitous genetic improvement in the bee park.

LEGEND

(1) Fitness: in biology it defines the reproductive success of an individual, in genetics the suitability of an organism for the environment, its adaptive value

(2) Homeostasis: attitude proper to all living beings to maintain around a predetermined and constant level the value of some peculiar parameters for survival, continuously related to internal and external factors

(3) Reproductive value: is the value of an individual calculated on the average value of his offspring

(4) Haplotype: combinations of allelic variants within a chromosomal segment

(5) Motility: complex of the motor functions of an organism and its ability to change its position

(6) Senescence: aging process of an individual accompanied by involutional phenomena of physiological and functional type

(7) Transovarial transmission: the transmission from progenitors to offspring of pathologies through one’s own reproductive organs