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In the last few years successful queen selection and breeding has reduced the incidence of nosema in Denmark from around 70-80% to 10% or less. This is a significant achievement in a country with 4,700 beekeepers and about 170,000 colonies. Nosema levels have been the focus of their breeding effort for 25 years as the long, mild, humid, winters made this a major concern for Danish beekeepers. Nosema ceranae was detected in Denmark in 2003.

 

Queen breeding, as in much of the EU, is well organised, with 20 islands, peninsulas, and spits set aside by legislation for mating areas. Performance tests of the breeder queen's offspring are conducted, with blind trails and full publication of the annual results in the local beekeeping magazine. A crucial development in the early 1980s enabled digital camera analysis of nosema spore counts. The was provided by a school looking for a way to engage troublesome teenagers at E3.5 (NZD6.00) per sample, and now every April a 60 bee sample (of the over-wintered adults) is taken from all potential breeder queens (@400 colonies). Prior to breeding any with nosema are excluded.

 

With both resistant and non-resistant strains available researchers are much more able to investigate the genetic basis of the phenomenon. An early study in 2012 found, six days post infection, several immune mechanisms were (to use the jargon) 'up-regulated' in response to the infection. The heightened immunity was keeping the infection at bay. Last week another ( Open Access) paper described how the work is continuing, using a colony from Denmark and one from France. Mostly over my head, it explained the evidence for their proposal that N.ceranae interferes with the expression of a gene regulating programmed cell death (apoptosis). Infected cells should be 'killed off' and shed into the gut where they can be excreted, but by interfering with this process the parasite is able to delay or halt the mechanism so that it can continue to reproduce and infect more of its host. There is already evidence of programmed cell death in mammals as a response to similar infections by protozoans, and it is a well-known immunity 'tool' in wide-spread use across the animal kingdom.

 

Huang Q, Kryger P, Le Conte Y, Moritz RFA. (2012) Survival and immune response of drones of a Nosemosis tolerant honey bee strain towards N. ceranae infections. J Invertebr Pathol.; 109(3):297–302. doi:10.1016/j.jip.2012.01.004

 

Kurze C, Le Conte Y, Dussaubat C, Erler S, Kryger P, Lewkowski O, et al. (2015) Nosema Tolerant Honeybees (Apis mellifera) Escape Parasitic Manipulation of Apoptosis. PLoS ONE 10(10):e0140174. doi:10.1371/journal.pone.0140174

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