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The western honey bee, Apis mellifera, is recognised as the most important pollinator for more than a thousand wild and cultivated plants¹. However, it was in the mid-20th century that an infestation by the Varroa mite, Varroa destructor, was first detected². Varroasis, as the mite infestation of a bee colony is known, has a wide range of adverse pathological effects on a honeybee population and represents the greatest threat to date to Apis colonies. arguably the biggest problem is the transmission of viruses, such as the wing deformation virus³. Without treatment with an acaricide, a mite infestation leads to the collapse of the entire bee colony within one to four years. However, this treatment method does not provide a permanent solution, as there is a risk that mites will develop resistance to the chemicals used. Consequently, increasingly higher concentrations would be required for effective Varroa treatment, which, in the worst-case scenario, could also harm the bees². For this reason, an alternative is urgently being sought.
One possible approach is the targeted breeding of honey bees for natural, heritable traits of resistance or tolerance to Varroa infestation⁴. The focus is on the so-called SMR (Suppressed Mite Reproduction) traits of Varroa-resistant bee colonies, which enable the bees to independently keep the number of mites in the colony below a certain damage threshold, thereby preventing any negative effects from the Varroa infestation⁵. There are already several honeybee populations around the world, such as colonies in Sweden or France, which, due to their SMR traits, are infested with Varroa mites to a significantly lesser extent. These colonies and their genetic, evolutionary and epidemiological mechanisms form the basis for research into Varroa tolerance traits⁶.
In collaboration with the Saxony Regional Association for Varroa-Resistant Breeding (Landesverband Sachsen für Varroaresistenzzucht e.V.), a method in the form of a rapid genetic test is to be developed to genetically evaluate the resistance traits of a queen bee, which is essential for successful breeding.
By isolating DNA from the nymphal cuticle of a newly emerged queen of the genus Apis mellifera and subsequently performing nanopore sequencing, each queen bee is tested for her SMR behaviour. To this end, beekeepers from the LSV have provided queen cells for genetic analysis, from which the nymphal casings can be isolated. Nymphal casings are a chitinous skin (cocoon) which the queen bee leaves behind in the wax-lined queen cell after hatching. DNA has already been successfully isolated from the provided nymphal casings using an isopropanol precipitation method. Following the initial sequencing runs, DNA sequences belonging to the genus Apis, as well as DNA from various microorganisms, were detected. The Apis sequences identified were subsequently examined for genes and gene regions associated with Varroa resistance, as described in the literature. The focus here is on genetic markers and single nucleotide polymorphisms (SNPs) associated with resistance to Varroa destructor⁴. Some of these marker genes were already detectable among the Apis sequences identified.
Cindy Moeller has been studying at Mittweida University of Applied Sciences since 2018, initially on the Bachelor’s degree programme in Biotechnology and, since 2021, on the Master’s degree programme in Genomic Biotechnology. In her Master’s thesis, she is working with Professor Röbbe Wünschiers and Lisa Prudnikow on the genetics of varroa-resistant bees.
Endnotes
1 Papa, Giulia; Maier, Roberto; Durazzo, Alessandra; Lucarini, Massimo; Karabagias, Ioannis K.; Plutino, Manuela et al. (2022): The Honey Bee Apis mellifera: An Insect at the Interface between Human and Ecosystem Health. In: Biology 11 (2). DOI: 10.3390/biology11020233.
2 Kaskinova, M. D.; Gaifullina, L. R.; Saltykova, E. S.; Poskryakov, A. V.; Nikolenko, A. G. (2020): Genetic markers for honey bee resistance to Varroa destructor. In: Vavilov Journal of Genetics and Breeding (24), Article 8, pp. 853–860.
3 Rosenkranz, P.; Aumeier, P.; Ziegelmann, B. (2010): Biology and control of Varroa destructor. In: Journal of Invertebrate Pathology (103), pp. 96–119.
4 Mondet, F.; Beaurepaire, A.; McAfee, A.; Locke, B.; Alaux, C.; Blanchard, S. et al. (2020): Honey bee survival mechanisms against the parasite Varroa destructor: a systematic review of phenotypic and genomic research efforts. In: International Journal for Parasitology (50), pp. 433–447.
5 Boecking, O., Spivak, M. (1999) Behavioural defences of honey bees against Varroa jacobsoni Oud., Apidologie 30, 141–158.
6 Zakar, E.; Javor, A.; Kusza, Sz. (2014): Genetic bases of tolerance to Varroa destructor in honey bees (Apis mellifera L.). In: Insectes Sociaux (61), pp. 207–215