Under the Microscope: Mitigating Varroa
UNDER THE MICROSCOPE BROUGHT TO YOU BY dnature
By John Mackay
Varroa continues to be the biggest issue for NZ beekeepers. While we wait for the results of the latest Colony Loss Survey, we can look over the 2020 results in the infographic here.
Varroa losses were a leading cause of colony losses in 2020, nearly equal with queen issues. Anecdotal reports this year of major hive losses, with deformed wing virus symptoms in many, suggest the 2021 reading of varroa-related colony losses will not be pretty. A worse situation would be if these losses have not been reported, therefore the issues not highlighted, then beekeepers have few avenues for any investigation or research into potential causes.
This month, we look at some new pieces of work on ways of potentially mitigating some of the effects of varroa. The first looks at repairing the physical puncture wound made by varroa.
Researchers in Turkey (Özkırım & Küçüközmen 2022) looked at the wounds in the outer hard layer of the bees – a potential source of otherwise harmless bacteria entering and causing disease. Of course viruses may also be entering – but more via injection by varroa. The researchers looked at using chitosan (think prawn and crab shell in a gel) to heal the varroa wounds and mitigate the physical puncture wounds.
Compared to a group with untreated puncture wounds, punctured bees treated with chitosan in different doses healed within three to six days (depending on the amount of chitosan applied) while the untreated bees healed in nine days. Also, the treated bees did not suffer the hair loss that the untreated bees had, suggesting that infection at the puncture sites may be responsible for the hair loss observed.
As an application, chitosan is soluble in varroa-treatment acids such as oxalic acid and thus may be an interesting additive to study in future. However there are limitations to this work. While we now know that varroa get under the abdominal plates to feed on the fat body of bees, this work focussed on thorax-based punctures. Therefore any benefits will need investigation in real-world varroa infestations.
Propolis to Cure the Ails?
Another recent paper (Pusceddu, Annoscia et al, 2021) looked at whether propolis was being used as a self-medication against varroa. The benefits of propolis on decreasing nosema and viruses in a colony have been studied to a limited extent but typically by applying propolis to the walls of a hive.
This new work determined that bees were actually applying propolis to the brood cells prior to eggs being laid by the queen. Then, using artificial cells with and without a propolis layer, the researchers demonstrated that the propolis lowered varroa levels and mortality rates of bees being raised in these cells. Interestingly, the bees actively sought to medicate – when comparing the levels of propolis taken by varroa-infected and non-affected bees, those with varroa took up more of the propolis food.
The anti-microbial affects of manuka honey are well-known. However the anti-microbial affects of the plants themselves are being increasingly studied for their ability to decrease bacterial and pathogen runoff levels when used in riparian planting.
Do bees collect propolis from manuka and kanuka…?
John Mackay is a molecular biologist and the technical director of Gisborne-based lab dnature Diagnostics and Logistics, as well as a hobby beekeeper.
Aslı Özkırım & Billur Küçüközmen (2022) Chitosan-based gel application on model bees (Apis mellifera L.) for healing bite wounds caused by Varroa destructor, Journal of Apicultural Research, 61:1, 45-51, DOI: 10.1080/00218839.2021.1935129
Pusceddu M, Annoscia D, Floris I, Frizzera D, Zanni V, Angioni A, Satta A. Nazzi F. (2021) Honeybees use propolis as a natural pesticide against their major ectoparasite. Proc. R. Soc. B 288: 20212101. https://doi.org/10.1098/rspb.2021.2101