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

Melissococcus plutonius is a bacterial pathogen that causes epidemic outbreaks of European foulbrood (EFB) in honey bee populations. The pathogenicity of a bacterium depends on its virulence, and understanding the mechanisms influencing virulence may allow for improved disease control and containment. Using a standardized in vitro assay, we demonstrate that virulence varies greatly among sixteen M. plutonius isolates from five European countries. Additionally, we explore the causes of this variation. In this study, virulence was independent of the multilocus sequence type of the tested pathogen, and was not affected by experimental coinfection with Paenibacillus alvei, a bacterium often associated with EFB outbreaks. Virulence in vitro was correlated with the growth dynamics of M. plutonius isolates in artificial medium, and with the presence of a plasmid carrying a gene coding for the putative toxin melissotoxin A. Our results suggest that some M. plutonius strains showed an increased virulence due to the acquisition of a toxin-carrying mobile genetic element. We discuss whether strains with increased virulence play a role in recent EFB outbreaks

Authentication of the botanical origin of honey using profiles of classical measurands and discriminant analysis

The potential of physical and chemical measurands for the determination of the botanical origin of honey by using both the classical profiling approach and chemometrics was evaluated for the authentication of ten unifloral (acacia, rhododendron, chestnut, dandelion, heather, lime, rape, fir honeydew, metcalfa honeydew) and polyfloral honey types (in total n = 693 samples). The classical approach using a profile for the determination of the botanical origin of honey revealed that the physical and chemical measurands alone do not allow a reliable determination. Pollen analysis is therefore essential for discrimination between unifloral and polyfloral honeys. However, chemometric evaluation of the physical and chemical data by linear discriminant analysis allowed reliable authentication with neither specialized expertise nor pollen or sensory analysis. The error rates calculated by Bayes' theorem ranged from 1.1% (rape and lime honeys) up to 9.9 % (acacia honey

Honey bee brood ring-test: method for testing pesticide toxicity on honeybee brood in laboratory conditions

contribution to session IV Test methodology The Experimental unit of entomology (INRA, France) developed a new in vitro method to assess effects of pesticides on honey bee larvae. The method consists in rearing bee larvae in plastic cells. The larvae are fed with diet containing 50% of fresh royal jelly and 50% of an aqueous sugar and yeast extract solution, and reared in an incubator at 35 °C and 96% relative humidity. According to that method, 9 tests (7 in 2008 and 2 in 2005) were carried out in 7 laboratories and different countries. The objective of these trials was to assess the LD50 for dimethoate 48 hours after an acute exposure. The LD50 values ranged from 1.5 μg a.i./larva to 8.8 μg a.i./larva, with 2 tests with particularly high values (5.0 and 8.8 μg a.i./larva). In 7 tests, these values ranged from 1.5 μg a.i./larva to 3.1 μg a.i./larva. Such variability may be due to the colony origin, the season and larva heterogeneity at grafting. Solutions are proposed to improve the method through the continuation of the ring test. Keywords: Apis mellifera, brood, in vitro test, dimethoat

Residues in wax and honey after Apilife VAR® treatment

Apilife VAR®, with thymol as its main active ingredient, is registered for use against Varroa jacobsoni Oudemans in Switzerland. After Apilife VAR® treatment in autumn of 1992, the residues in honey and comb were examined the following spring. Only thymol residues were found in honey, whereas in comb the residues consisted of 99 % thymol and 1 % menthol. The thymol residues in honey did not increase with an increasing number of treatments and varied between 0.02 to 0.48 mg·kg-1 with an average of 0.15 mg·kg-1 (n = 29). The taste threshold of thymol in acacia and rape honey was between 1.1 and 1.6 mg·kg-1. The brood comb in two apiaries, where Apilife VAR® was used for, on average, 4 consecutive years, had a mean content of 574 mg·kg-1 and this did not increase with an increasing number of treatments. The thymol residues in honey comb were on average 21.6 mg·kg-1. Thymol did not evaporate during comb melting, but decreased rapidly when comb and foundation were exposed to the air during storage. © Inra/DIB/AGIB/Elsevier, Pari

ÜBERPRÜFUNG DER SCHÄTZMETHODE ZUR ERMITTLUNG DER BRUTFLÄCHE UND DER ANZAHL ARBEITERINNEN IN FREIFLIEGENDEN BIENENVÖLKERN

International audienc

Nitrogen and mineral constituents of honey bee worker brood during pollen shortage

Bee colonies were prevented from collecting pollen, and the effect on brood rearing and on the N, P, K, Ca, Na and Mg contents of pupae was studied. Under these conditions brood rearing was reduced and fully stopped, which lead to a decrease in population size, whereas control colonies with access to pollen developed normally. Only a few significant differences were found in chemical analyses in pupae and worker bees of colonies with and without access to pollen. We conclude that the major feature of honey bee response to pollen shortage is a termination of brood rearing, and that those pupae still reared contain similar quantities of nitrogen and of most minerals as pupae reared during good foraging conditions. © Inra/DIB/AGIB/Elsevier, Pari

Determination of residues in honey after treatments with formic and oxalic acid under field conditions

Formic acid and oxalic acid field trials for control of Varroa destructor were carried out in autumn according to the Swiss prescriptions during three successive years in different apiaries in Switzerland. The following parameters were determined in honey that was harvested the year after treatment: formic acid, oxalic acid and free acidity. The following range of values were found in honeys of untreated colonies: formic acid, from 17 to 284 mg/kg, n = 34; oxalic acid, from 11 to 119 mg/kg, n = 33. There was a small, but unproblematic increase in formic acid levels in comparison to the levels in the controls; average: 46 mg/kg, maximum: 139 mg/kg. No increase in formic acid was found with increasing number of treatment years. If emergency formic acid treatments were carried out in spring, the residue levels were much higher: average increase of 193 mg/kg, maximum 417 mg/kg. The oxalic acid content remained unchanged, even after two successive treatments during the same autumn. No rise of free acidity was encountered after a combined treatment with formic and oxalic acid during the three trial years

Impact of the Asian Chestnut Gall Wasp, Dryocosmus kuriphilus (Hymenoptera, Cynipidae), on the Chestnut Component of Honey in the Southern Swiss Alps

The Asian chestnut gall wasp (ACGW; Dryocosmus kuriphilus Yasumatsu, Hymenoptera, Cynipidae) is considered as one of the most dangerous pests of the genus Castanea. In southern Switzerland, repeated heavy ACGW attacks prevented chestnut trees from vegetating normally for years before the arrival and spread of the biological control agent Torymus sinensis (Kamijo, Hymenoptera, Torymidae). This resulted in a greatly reduced green biomass and flower production. In this paper, we analyze the impact of such an ecosystem alteration of the environment on the composition of produced honey. Six beekeepers were chosen from sites with different densities of chestnut trees, each of which providing series of honey samples from 2010 to 2016. We determined the chestnut component in the honeys via a combined chemical and sensory approach, and correlated the obtained results with the degree of yearly ACGW-induced crown damage and weather conditions during the period in question in the surrounding chestnut stands. The chestnut component in the analyzed honey sample series showed a strong correlation with the degree of ACGW-induced crown damage, whereas meteorological conditions of the corresponding year had a very marginal effect. Decreases in the chestnut component of the honey were statistically significant starting from a ACGW infestation level of 30%