A defining feature of social insects is the reproductive division of labour, in which workers usually forego all reproduction to help their mother queen to reproduce. However, little is known about the molecular basis of this spectacular form of altruism. Here, we compared gene expression patterns between nonreproductive, altruistic workers and reproductive, non-altruistic workers in queenless honeybee colonies using a whole-genome microarray analysis. Our results demonstrate massive differences in gene expression patterns between these two sets of workers, with a total of 1292 genes being differentially expressed. In nonreproductive workers, genes associated with energy metabolism and respiration, flight and foraging behaviour, detection of visible light, flight and heart muscle contraction and synaptic transmission were overexpressed relative to reproductive workers. This implies they probably had a higher whole-body energy metabolism and activity rate and were most likely actively foraging, whereas same-aged reproductive workers were not. This pattern is predicted from evolutionary theory, given that reproductive workers should be less willing to compromise their reproductive futures by carrying out high-risk tasks such as foraging or other energetically expensive tasks. By contrast, reproductive workers mainly overexpressed oogenesis-related genes compared to nonreproductive ones. With respect to key switches for ovary activation, several genes involved in steroid biosynthesis were upregulated in reproductive workers, as well as genes known to respond to queen and brood pheromones, genes involved in TOR and insulin signalling pathways and genes located within quantitative trait loci associated with reproductive capacity in honeybees. Overall, our results provide unique insight into the molecular mechanisms underlying alternative reproductive phenotypes in honeybee workers.

Honey bees are under pressure due to abnormal high colony death rates, especially during the winter. the infestation by the Varroa destructor mite and the viruses that this ectoparasite transmits are generally considered as the bees' most important biological threats. Almost all efforts to remedy this dual infection have so far focused on the control of the Varroa mite alone and not on the viruses it transmits. In the present study, the sanitary control of breeding queens was conducted on eggs taken from drone brood for 4 consecutive years (2015-2018). The screening was performed on the sideline of an ongoing breeding program, which allowed us to estimate the heritabilities of the virus status of the eggs. We used the term 'suppressed in ovo virus infection' (SOV) for this novel trait and found moderate heritabilities for the presence of several viruses simultaneously and for the presence of single viral species. Colonies that expressed the SOV trait seemed to be more resilient to virus infections as a whole with fewer and less severe Deformed wing virus infections in most developmental stages, especially in the male caste. The implementation of this novel trait into breeding programs is recommended. The economic value of the honey bee can be almost entirely attributed to its pollination services for agricultural crops 1. However, honey bees are under pressure due to abnormal high colony death rates, especially during the winter 2. There are several possible explanations for the increased mortality, but the infestation by the Varroa destructor mite and the viruses that this ectoparasite transmits are generally considered the most important biotic threats 3,4. The mite was found to be an efficient vector of viruses even to the extent that initially the clinical symptoms caused by the Deformed wing virus (DWV) were wrongly attributed to the mite 5. The Varroa mite and DWV interact in many different ways, resulting in an increase in DWV virulence 6,7 and colony mortality 8-12. These effects are partially due to the mutualistic symbiotic relationship between both, in which the mite provides transmission of the virus when it feeds on the bee, whereas the virus undermines the immunity of the honey bee by interfering with NF-κB signaling, possibly facilitating the mite's trophic activity 13. Almost all efforts to remedy this dual infection have so far focused on the control of the Varroa mite alone. Indeed, several mitecontrol strategies have been set up in beekeeping practice that rely on acaricide medication or other treatments, biotechnical apicultural methods and selection for Varroa resistance 14. The control of the viruses transmitted by the mite is therefore achieved almost exclusively indirectly, by limiting the severity of the mite infestation. One exception to this is the treatment with double-stranded RNA to provoke a targeted antiviral immune response based on RNA interference, but this is rarely used in beekeeping practice 15,16. The transmission of viruses between bees by the vectoring Varroa mite is descr...

The honey bee ectoparasite Varroa destructor is considered the major threat to apiculture, as untreated colonies of Apis mellifera usually collapse within a few years. In order to control this mite, many beekeepers rely on a limited number of approved synthetic acaricides, including the pyrethroids tau-fluvalinate and flumethrin. Due to the intensive use of these products, resistance is now commonplace in many beekeeping regions across the world. In the present study, the occurrence of amino acid substitutions at residue L925 of the voltage-gate sodium channel-the pyrethroid target site-was studied in Varroa populations collected throughout Flanders, Belgium. Dose-response bioassays supported the involvement of the frequently observed L925V substitution in flumethrin resistance, resulting in a 12.64-fold increase of the LC 50 in a Varroa population mostly consisting of homozygous 925 V/V mites. With the presence of L925 substitutions in about four out of 10 screened apiaries, the use of pyrethroid-based varroacides in Flanders, including the recently released PolyVar® Yellow, should be carefully considered.

No abstract

VarroMed® is a soft acaricide registered for honey bees on the European Union market since 2017 for Varroa control. Researchers involved were partners of different countries of the Varroa control task force of the COLOSS Association. Our goal was to evaluate performances (acaricide efficacy and toxic effects on honey bees) of VarroMed® in different climatic conditions. Our results in the tested apiaries showed an efficacy ranging from 71.2 to 89.3% in summer/autumn, and from 71.8 to 95.6% in winter. No toxic effects on bees were observed, except in one apiary, where severe cold climatic conditions played a crucial role. The treatment could be efficiently applied in broodright as well as in broodless colonies. Integrated pest management (IPM) recommendations for beekeepers are provided in order to apply the best Varroa control protocol.