Ascosferiosis is an invasive mycosis that affects exclusively the larvae at three, four days of life. Also known as “create chalk”, due to its characteristic appearance and consistency that resemble the plaster fragments.
It is the most frequent mycosis of the bee producing honey and is produced by the fungus Ascosphaera apis, which causes serious problems to the colonies by the contagion and pathogenesis that it presents.
The breeding with ascospheriosis has become, in recent years, a serious problem for the world. At the moment, it is very expanded by Europe, North America, some countries of South America, Central America, Africa and Oceania.
The Ascosphaera apis fungus belongs to the Ascospherales Order, Family Ascosphaeraceae. This mycosis is also caused by the action of Ascosphaera major and A. proliperda.
The fungus has optimal growth temperatures of 15 to 37 ° C. It grows well in vitro in sugars and peptone rich media, with ph7, and supports better the acidity conditions than those of alkalinity. It grows well in aerobiose and concentrations of 5% to 10% of CO2 favor its development.
It is endowed with an ample equipment destined to the degradation of the sugars, very abundant in the environment in which they develop. It also has an enzyme of vital importance to its pathogenic mechanism.
The spores are hyaline and ellipsoidal with 2 x 3 mm, elements of conservation and dissemination of the disease, and have a surface that allows them to adhere to different substrates. They can be found in honey, stored pollen, wax and on the body and intestine of adult bees, in healthy and diseased hives.
They have a high resistance, due in part to the thick wall (30% of spore diameter), can remain viable for more than 15 years in the environment, 1 year in pollen and 2 years in honey. They support temperatures of 16 ° C for 6 days and 40 ° C for more than one month, easily surviving at the melting temperature of the wax, formaldehyde and high concentrations of sulfuric acid. They germinate in an atmosphere rich in carbon dioxide (12%) and resist ultraviolet radiation.
The offspring presents some characteristics of great importance. One of these is the variation in levels of infection; a beekeeper can put in his apiary little affected hives and others with great mortality in their offspring. The reasons for this lie in the intrinsic resistance of each colony to diseases.
The emergence and evolution of the disease are related to the stress generated by different causes: it is not only due to the ingestion of spores by the larvae (reinfection), but also to the performance of environmental factors and the handling of the young.
A large number of contingencies are capable of causing stress on hives; the quantity and diversity of these may vary according to the geographical area in which the beekeeping activity takes place. Among the best known, they may refer to:
– Cooling of the baby: this is the most important factor. No major exposure to low temperatures is necessary to trigger the disease.
– Nursery / breeding imbalances: when the nesting bees population is not adequate, the temperature of the nest can not be maintained in normal form.
– High humidity and poor ventilation.
– Deficiencies with food: caused by a poor supply of pollen.
– Improper and excessive handling.
– Suffering from other diseases and infections caused by Varroa jacobsoni.
Ascosphaera apis is a heterotálico fungus and produces elements of resistance and dispersion (spores) that are ingested by the larvae with the food, causing, in this way, the infection.
The reproductive phenomenon involves the intervention of two types of mycelium that are commonly called male and female (+) and (y). When both grow together, the female mycelium develops two reproductive structures that have the name of nutriocyst and tricogino.
The spores germinate in the posterior part of the midgut and the formed mycelium begins to grow, invades the tissues, crosses the cuticle, emerges to the surface of the larva and recovers almost entirely the larval body.
Although larvae may ingest spores throughout the feeding stage, it was determined that the period of greatest susceptibility corresponds to the time that goes from the operation. In principle, the dead larvae present a cottony appearance and then dry and mummify.
The final appearance of the mummies will be white if the mycelium involved is of a single sexual sign, and black if the mycelium presents hyphens of different sexes, which when copulating produce the fruiting bodies responsible for their coloring.
The mummies may be on the ground or at the entrance or on the floor of the hive, removed by the wipers. They can also be found in combs, both in unselected and operculated cells.
Ascosphaera apis appears in principle on the breeding of the drone, to extend later to the creation of workers, although it is not a strict rule.
In the apiary the presence of “mummies” extracted by the cleaning bees on the flight board or in front of the hives is observed, observing a depopulation and a low activity in the affected hives.
The infected larvae present initially a cotton consistency, due to the extension of the mycelium. The water in the tissues evaporates and mummification begins to harden the baby.
The larvae inside the crafted cells are not adhered to the walls and this causes a noise when the frame is moved.
The irregular arrangement of the posture that is obtained by the cleaning of mummies, not being infected all the larvae and the new posture of the queen, causes that it is presented in mosaic.
The “mummies” remain a dirty white color, if they did not produce spores; otherwise, their coloration is bluish gray or almost black.
The spread of disease through spores occurs in different ways:
Among healthy and sick hives:
– By producing looting on the colony much affected by the fungus, the bees return to the same hives with a load of spores adhering to their body.
– The bees of diseased colonies that lose their way and return to hives that are not theirs.
– Parasites of Varroa jacobsoni are vectors of the importance of the disease.
– Through the course of healthy bees to floral sources already visited by bees from sick hives.
– The beekeeper himself, through improper handling, interferes with the spread of spores of Ascosphaera apis.
Inside the same hive:
– By trofalaxia (transfer of food from one adult bee to another)
– Feces and remains of diseased larvae inside the cell.
Clinical: In the field, this ringworm is easily diagnosed. The affected hives present mummies in different places of the hive (floor and frames), as well as in the vicinity of the hole.
Laboratory: A microscopic analysis of the fungus is performed to determine the species involved in the onset of the disease.
It is necessary not to confuse Ascosphaera apis with another type of fungus, Aspergillus flavus, an etiological agent of the mycosis called “putrid”, which has a much lower incidence than A. apis and affects both larvae and adult bees. It produces aspergillosis in the male (mucosal and conjunctive irritation). Another fungus present inside the hive is Bettsia alvei, which fundamentally affects stored pollen, which is not consumed by bees. The aspect it presents makes it known as “pollen mold”.
Nowadays, the work done to achieve the control of Ascosferosis goes in three directions:
– Search for chemical agents
– Handling practices
– Genetics of bees.
The ventilation of the hive should be monitored because the excessive opening can cause the temperature of the nest of the young to approach the good temperature for development of the fungus (30ºC) and a poor ventilation favors the sporulation of the infectious agent due to the excess of anhydride carbon dioxide produced by the respiration of the baby and the bees.
Where the hive is located should be located in a sunny location, be prepared to prevent soil moisture from being transmitted to hives and water courses not too close to hives.
The systematic exchange of the breeding chamber is important because, on the contrary, the increase of spores inside the hive is favored.
Protein feed is important for the development of the young and excessive use of pollen has a negative effect on the ascosferiosis process.
The presence of the infectious agent is not sufficient reason to present the disease, other factors are necessary to trigger the onset of mycosis on the farm.
Preventive measures are the most effective.
An ideal antifungal should be innocuous for adult bees and creates, does not leave residues in bee products, be persistent and easy to study. These characteristics, in general, are not fulfilled as a whole.
It is necessary to emphasize the importance of not using chemical agents indiscriminately and without knowledge, not only in the perspective of being toxic to bees or leaving residues in honey, but also because of the appearance of resistant cells of Ascosphaera apis.
Recommended handling practices are aimed at reducing stress (preventing predisposing factors) and infecting mass (reducing spore load).
It is important to avoid the opening of hives on cold days, the displacement of broodstock to places in the colony where care and temperature are not sufficient, feeding with syrup at inappropriate times; keep hives with the right population. The use of pollen traps should be limited and ventilation should be provided for hives.
The onset of an outbreak results in the accumulation of spores within the hive, so it is necessary, along with the prevention of predisposing factors, to eliminate the largest number of infecting forms, removing the old ones, and avoiding to exchange material between healthy and diseased hives .
It should be borne in mind the possibility of the queen’s exchange in those colonies where the disease reappears. Hives badly affected should be isolated or killed, if necessary, by burning pictures and burning bins.