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Lithium chloride leads to concentration dependent brood damages in honey bee hives (Apis mellifera) during control of the mite Varroa destructor
(2022) Rein, Carolin; Makosch, Marisa; Renz, Julia; Rosenkranz, Peter
Lithium chloride (LiCl) has a high efficacy against Varroa destructor and a good tolerability for adult bees but the effect of LiCl on the honey bee brood has not been taken into consideration yet. We quantified the mortality of larvae fed with different concentrations of LiCl. For artificially reared larvae already, a concentration of 1 mM had significant toxic effects while under colony conditions, 10 mM was well tolerated. However, a chronic application of the effective concentration of 25 mM elicited brood mortalities between 60 and 90%. Shorter feeding periods of 2 or 4 days reduced the brood damages significantly. Measurements of the lithium concentrations in larvae and pupae during a chronic exposure with 10, 17.5 and 25 mM LiCl revealed respective lithium levels in 5th instar larvae of 7, 13 and 15 mg/kg. No lithium was detectable in 2-day old larvae indicating that pure worker jelly from the hypopharyngeal gland is not contaminated with LiCl. Based on these results, applications of LiCl in colonies with brood should be avoided.
Rapid transformation of traditional beekeeping and colony marketing erode genetic differentiation in Apis mellifera simensis, Ethiopia
(2022) Hailu, Teweldemedhn Gebretinsae; Rosenkranz, Peter; Hasselmann, Martin
Subsistent beekeeping has been an established tradition in Tigray, northern Ethiopia. In the last two decades, extension efforts tried to transform it into improved apiculture, which led to development of colony marketing. Here, we assessed the progress in beekeeping, colony marketing, and population differentiation with a hypothesis that the extension might have supported both production and genetic conservation in accordance with the national apiculture proclamation. Progress in beekeeping was analyzed based on official annual reports from 2004 to 2020. In addition, colony market survey was conducted in one of the central markets to analyze spatial and agro-ecological zone (AEZ) distributions of the honey bees, driving factors, and implications by interviewing 120 sellers and buyers. Moreover, highland and lowland honey bee population differentiation was compared in two areas (not-) involved in marketing using a nuclear marker known for elevational adaptation. The regional beekeeping progressed substantially: frame hives grew from 1 to 23%, annual honey production tripled, managed colonies increased by 90%. Frame hives provided significantly (F = 88.8, P < 0.001) higher honey yield than local hives. Colonies were exchanged between actors with significant differences in spatial (X2 = 104.56, P < 0.01) and AEZ (X2 = 6.27, P = 0.044) distributions. Colonies originate mainly from highland areas of two districts and were re-distributed to broader areas. Most buyers showed preferences for colony color (73.3%) and AEZ of origin (88.3%), which led to a one-way flow. Consequently, no genetic differentiation was detected between two contrasting elevations in the involving district compared to a not involving area (FST = 0.22). Overall, the regional apiculture progressed significantly, but there is no evidence that the extension contributed to conservation.
Reproduction of Varroa destructor does not elicit varroa sensitive hygiene (VSH) or recapping behaviour in honey bee colonies (Apis mellifera)
(2021) Sprau, Lina; Hasselmann, Martin; Rosenkranz, Peter
Suppressed mite reproduction (SMR) is an important trait for the selection of Varroa resistant honey bee colonies. It has repeatedly been assumed that SMR is an effect of varroa sensitive hygiene (VSH) when hygienic bees preferably remove those brood cells where the mite has reproduced. We here compare the VSH behaviour of honey bees toward brood cells artificial infested with a varroa mite. By infesting half of the brood cells directly after the cell capping and the other half only 24 h later, we established two groups with high (> 75%) and low (< 2%) mite reproduction. After 8 days, about 40% of the infested brood cells were removed, however without any difference between both groups. Likewise, no group differences were recorded in the percentage of recapped brood cells. This strongly indicates that the presence of mite offspring is not a crucial trigger for the VSH behaviour. SMR data like the percentage of non-reproducing mites are therefore not the optimal measure for the selection of colonies with high VSH.

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