Bacteria such as American and European foulbrood, fungi such as Chalkbrood and Stonebrood and others are well researched and some has controlled methods. In recent years, the Nosema has become a major factor in the colony health and the understanding of this single cell gut parasite is maturing.
Nosema (apis, cerana)
Nosema disease is one of the most prevalent adult honey bee diseases and
is caused by two described species of microsporidia, Nosema apis and Nosema
ceranae. Transmission of Nosema in honey bee colonies is mainly via the
fecal-oral route in which pathogens are spread by transferring feces of
diseased hosts to uninfected hosts via ingestion. Adult bees ingest Nosema
spores when they are eating contaminated food and when they are cleaning
up fecal material from infected bees. The spores geminate within the midgut
and release polar tubes that transfer their sporoplasm into midgut epithelial
cells where they generate more spores. Millions of new spores can be found
inside of a bee's midgut a few weeks after initial infection, and the
spores excreted with feces become new sources of the infection in the
colonies. Although infected bees do not exhibit obvious external disease
symptoms, infection of Nosema causes digestive disorders, shortened life
spans, decrease of population size, and reduction of honey production
and crop products that rely on bees for pollination.
Nosema is widespread across the world in both its apis
and cerana morphs. An article published in Science magazine in September
2007 by a team led by Professor Diana Cox-Foster
found that there was extensive coverage of Nosema in almost all samples
taken in both collapsed and apparently healthy control hives.
Nosema ceranae may have recently jumped from its primary
host, the Asian honey bee Apis cerana, to the worldwide honey producer,
A. mellifera. However, the fact that Nosema cerana has been detected in
American Apis mellifea honey bees since at least 1996 points to the conclusion
that Nosema apis spores have been incorrectly and/or mistakenly diagnosed
(at least) since then. Indeed, this indicates that N. ceranae may not
be a new emerging pathogen for European honey bees after all, and in fact
had transferred from its original host to Apis mellifera earlier than
previously recognized.
In recent years, Nosema cerana has been implicated in more pronounced virulence than that which was previously ascribed to Nosema apis. In Europe, disappearing colony syndrome has been directly attributed to Nosema ceranae. Nosema ceranae is very pathogenic when experimentally inoculated into A. mellifera and natural infection has been associated with a syndrome of gradual depopulation, copious colony death in autumn or winter, and poor honey production. In fact, the risk of colony depopulation is six times higher in colonies infected with N. ceranae than in uninfected ones.
Recently, Spanish researchers showed that natural N. ceranae infection can cause the sudden collapse of bee colonies, establishing a direct correlation between N. ceranae infection and the death of honey bee colonies under field conditions. Signs of colony weakness were not evident until the queen could no longer replace the loss of the infected bees. Furthermore, their results demonstrate that healthy colonies near to an infected hive can also become infected.
Fumagillin is an antibiotic which has proven effective
against both N. ceranae and N.apis infections. It is used extensively
in the United States where beekeepers drench their hives in sucrose solution
containing Fumagillin. Despite this, since new bees emerge constantly,
re-application is required several times a year. In Europe, Fumagillin's
use is prohibited. Of further concern is the possibility that Nosema,
multiplying in the millions in each bee gut, will eventually develop resistance
to Fumagillin. Experience has shown that this inevitably occurs sooner
rather than later which makes many beekeepers in the United States understandably
nervous about this possibility.
