High-resolution maps of Swiss apiaries and their applicability to study spatial distribution of bacterial honey bee brood diseases

Abstract

Honey bees directly affect and are influenced by their local environment, in terms of food sources, pollinator densities, pathogen and toxin exposure and climate. Currently, there is a lack of studies analyzing these data with Geographic Information Systems (GIS) to investigate spatial relationships with the environment. Particularly for inter-colonial pathogen transmission, it is known that the likelihood of a healthy colony to become infested (e.g., Varroosis) or infected (e.g., American foulbrood—AFB, European foulbrood—EFB) increases with higher colony density. Whether these transmission paths can actually be asserted at apiary level is largely unknown. Here, we unraveled spatial distribution and high-resolution density of apiaries and bacterial honey bee brood diseases in Switzerland based on available GIS data. Switzerland as ‘model country’ offers the unique opportunity to get apiary data since 2010 owing to compulsory registration for every beekeeper. Further, both destructive bee brood diseases (AFB and EFB) are legally notifiable in Switzerland, and EFB has an epizootic character for the last decades. As governmental data sets have to be ameliorated, raw data from the cantonal agricultural or veterinary offices have been included. We found a mean density of 0.56 apiaries per km2, and high resolution spatial analyzes showed strong correlation between density of apiaries and human population density as well as agricultural landscape type. Concerning two bacterial bee brood diseases (AFB, EFB), no significant correlation was detectable with density of apiaries on cantonal level, though a high correlation of EFB cases and apiary density became obvious on higher resolution (district level). Hence, Swiss EFB epizootics seem to have benefited from high apiary densities, promoting the transmission of pathogens by adult bees. The GIS-based method presented here, might also be useful for other bee diseases, anthropogenic or environmental factors affecting bee colonies.

Putative determinants of virulence inMelissococcus plutonius, the bacterial agent causing European foulbrood in honey bees

“…Virulence trade-off models predict that the virulence of a pathogen is inversely correlated to its transmission, because excessive virulence causes early host death, hindering the spread of the pathogen amongst the population [ 70 – 73 ]. However, human-induced changes in the rate of horizontal transmission may have altered the adaptive compromise between virulence and transmission in M. plutonius [ 17 , 74 , 75 ]. Increased contact between honey bee colonies due to human management may allow for the spread of highly virulent strains unable to spread to new hosts under more natural settings.…”

“…One of the most detrimental bacterial diseases affecting honey bees is European foulbrood (EFB). EFB is reported worldwide [ 15 ] and has emerged as an infectious disease since the mid-eighties in the United Kingdom, since the year 2000 in Switzerland and since 2010 in Norway [ 13 , 14 , 16 , 17 ]. High numbers of clinical cases have also been reported from Finland, France, Greece, Holland, Czechia and Italy [ 18 – 20 ], making EFB an economically important veterinary disease [ 18 , 21 ].…”

Estimates of genetic parameters for production, behaviour, and health traits in two Swiss honey bee populations

“…Apiaries with hives kept in groups and entries facing in the same direction are known to increase mite transfers between colonies (Dynes et al 2019; Seeley and Smith 2015). In addition, many regions in Switzerland have a high colony and apiary density per square kilometre (Fluri et al 2004;von Büren et al 2019), and colony density has been linked with mite re-invasion flows in neighbouring Germany (Frey and Rosenkranz 2014). These mite flows between colonies likely mask colony effects.…”

“…This could be because other resistance traits (for instance grooming, Varroa sensitive hygiene, suppressed mite reproduction, swarming) or more likely, a combination of such traits, may be more efficient defence mechanisms under Swiss conditions, as this is the case in certain naturally resistant populations (Locke 2016). It is unclear how hygienic behaviour could help to decrease the number of cases of the widespread European foulbrood, as the prevalence of this endemic disease is also highly influenced by colony density (von Büren et al 2019). For these reasons, the ability of hygienic behaviour to limit chalkbrood or European or American foulbrood prevalence should be assessed in the Swiss context.…”

Pathogenesis, Epidemiology and Variants of Melissococcus plutonius (Ex White), the Causal Agent of European Foulbrood

“…More than a third of healthy colonies in an apiary can maintain adult bees carrying the bacteria due to the proximity to other diseased apiaries (Belloy et al, 2007). In Switzerland, a high density of colonies and hives have been shown to promote the transmission of EFB (von Büren et al, 2019). Additionally, Abrol (2013) and Forsgren (2010) suggested that the robbing of honey and drifting bees contributed to the spread of the bacteria between colonies and apiaries, but in contrast Goodwin, Perry, & Houten (1994) suggested that the drift of bees is not an important to the spread of AFB.…”