Development and testing of novel varroa mite controls is an ongoing process in the beekeeping industry. In the past, varroa mites have developed resistance to certain chemical treatment products. This emphasizes the need for better management of this honey bee pest, including the integration of various control measures beyond synthetic miticides. Reducing reliance on these synthetic chemicals reduces the risk of mites developing resistance to them, thereby prolonging the effective lifespan of these products in beekeeping. One novel varroa mite control product that is upcoming in development and testing is a fungus called Metarhizium. Keep reading below to learn more about how this fungus may be an effective biocontrol in the battle against varroa mites.
Directed Evolution of Metarhizium Fungus Improves its Biocontrol Efficacy Against Varroa Mites in Honey Bee Colonies *
A specific type of fungus (Metarhizium brunneum) that
causes disease in varroa mites has been the focus of a study working on
developing a biological control that is able to function effectively as a
control for varroa mites under typical honey bee hive conditions. This fungus
is likely to control varroa mites by adhering spores to the exoskeleton of the
mite which then germinate and grow a long branching filament called a ‘hypha’ (collectively
referred to as mycelium). The hypha penetrates the mite exoskeleton and
proliferates in the mite’s internal tissues, effectively killing the mite. Initially,
this fungus showed promise as a biocontrol for varroa mites but was unable to
function effectively due to the high temperatures within honey bee hives. In
response to this result, researchers created new strains of the Metarhizium
brunneum fungus using techniques of traditional selection and
directed evolution. This process involved collecting mites that were killed by
the fungus and then growing and reproducing the fungus under conditions
designed to increase its heat tolerance and overall effectiveness as a
biocontrol of varroa mites in functioning hives. The resulting strains were
able to survive, germinate, and grow in honey bee hive temperature conditions
(35⁰C)
with efficacy of mite control greater than the original fungus strain and similar
to currently used treatments.
There is an ongoing shift away from the use of synthetic
chemical treatments in honey bee hives for reasons beyond the risk of pest and
disease resistance development. Concerns over the use of these synthetic
chemicals have been raised in the beekeeping industry in terms of their
long-term impacts on honey bees and their potential to contaminate hive
products intended for human use. Biological controls are an attractive option
for pest control due to their typically high specificity in affecting only the
intended target and low toxicity towards non-targets. This fungal biocontrol
also exhibits minimal residual effects both in agricultural settings and in the
natural environment. There are currently no biological controls available for
use in Canadian beekeeping.
As a final note on the topic of upcoming honey bee pest control
products, only treatment products that are registered for use in beekeeping in
Canada are to be used in Canadian beekeeping practices.
* Han J. O. et al. (2021) Directed evolution of Metarhizium
fungus improves its biocontrol efficacy against Varroa mites in honey
bee colonies. Sci. Rep. 11, 10582. Full text available ONLINE.
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