As beekeepers we often see the damage inflected by Varroa mites (Varroa destructor) at the colony level. When colonies are not managed vigilantly for Varroa mites, and populations of mites reach a critical level, they colony is significantly weakened and is at high risk of dying before or during the winter months. To better understand why Varroa mites cause colony loss it is important to explore the biology of Varroa mites including their host-parasite interaction. This week’s blog will specifically focus of Varroa mite feeding and the direct impacts feeding has on their honey bee host.
The Host-Parasite Interactions of Varroa Mites and Honey Bees: Varroa Mite Feeding
Varroa mites
remain the most widespread and economically damaging pest of honey bees1.
It is important to continue researching how Varroa mites target and parasitize
honey bees to develop new chemical treatments and improve management practices.
An aspect of Varroa mite biology that is worthwhile to discuss is how their
feeding practices directly impact honey bees.
Varroa
parasitizes both the adult bee and developing brood by feeding on both
hemolymph and fat bodies. However, more recent studies have identified that the
fat body is the primary feeding source for Varroa mites as this tissue plays a
critical role for honey bee immune function, pesticide detoxification, energy metabolism,
and overall health of the honey bee2. This means that damage inflicted
by Varroa mites to the fat body impacts the bee’s ability to protect itself
from pathogens such as viruses and bacteria, and to detoxify pesticides, which
overall weakens the bee and shortens their lifespan2.
Beekeepers
should consider the fact that the preferred feeding location of Varroa mites
(underneath the metasoma) is in an area not visible to them when inspecting
colonies. Therefore, when a beekeeper does identify a mite dorsally (on top) of
a bee, this often indicates the ventral (underneath) feeding locations are
already occupied by additional mites, and mite levels may be critically high
within the colony.
The feeding
process involves puncturing the bee’s cuticle using toothed chelicerae, and
then using their pharyngeal pump to extract nutrients1. Continuous
feeding weakens the host, reduces longevity, and facilitates viral infections1.
Exploring
other impacts of Varroa mite feeding, brood infested with mites leads to a
reduction in the body weight of newly emerged bees and malformed adult bees,
which indicates developmental stress and compromised health3. Reduced
body weight and malformation is caused by a combination of loss of nutrients, viral
transmission and suppressed immune function during development3. Bees
with compromised development have a reduced lifespan, which contributes to
weakened colonies and overall colony decline.
One of the
primary ways Varroa mite feeding directly impacts honey bees is their saliva
composition. The saliva of Varroa mites contains a complex mixture of bioactive
proteins and enzymes that disrupt host immunity and wound healing4.
Typically, when an insect’s cuticle is punctured the wound will naturally heal
to prevent hemolymph loss. However, when Varroa punctures the cuticle of a
honey bee the wound inflicted does not close properly suggesting that the
saliva interferes with normal healing4. Approximately 356 proteins
have been identified in the saliva of Varroa mites that can either interfere
with the immune response to heal wounds, or function as virulence factors,
enhancing the mite’s ability to infect the honey bee host5.
Furthermore, the saliva of mites contains various enzymes which protect the
mite against harmful compounds produced by the honey bee during feeding2,6.
These enzymes break down toxic compounds that are produced during feeding, and
other harmful compounds existing within the honey bee host, which provides the Varroa
mites an adaptive advantage to parasitism2,6.
The direct
damage inflicted by the Varroa mite through feeding is severe, and contributes
to weakened colonies and colony loss. However, there are other aspects of the
host-parasite interaction between Varroa mites and honey bees that contribute
to the overall colony decline associated with high Varroa mite levels. Next
week’s blog will further explore Varroa mite biology and how this parasite
transmits viruses to their host.
- Jeyapriya, G., Sumathi, E., Saminathan, V.R., Renukadevi, P., Sasikala, R., Priya, S.S., Kowsika, S. and Pradeep, S., 2025. Parasitic Mites of Honey Bees (Apis Spp.): A Detailed Review of Varroa destructor in Parasitism, Pathogen Transmission and its Management. Acta Parasitologica, 70(5), pp.1-25.
- Ramsey, S.D., Ochoa, R., Bauchan, G., Gulbronson, C., Mowery, J.D., Cohen, A., Lim, D., Joklik, J., Cicero, J.M., Ellis, J.D. and Hawthorne, D., 2019. Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph. Proceedings of the National Academy of Sciences, 116(5), pp.1792-1801.
- Martin, S.J., 2001. The role of Varroa and viral pathogens in the collapse of honeybee colonies: a modelling approach. Journal of Applied Ecology, 38(5), pp.1082-1093.
- Kanbar, G. and Engels, W.J.P.R., 2003. Ultrastructure and bacterial infection of wounds in honey bee (Apis mellifera) pupae punctured by Varroa mites. Parasitology research, 90(5), pp.349-354.
- Zhang, Y. and Han, R., 2019. Insight into the salivary secretome of Varroa destructor and salivary toxicity to Apis cerana. Journal of Economic Entomology, 112(2), pp.505-514.
- Morfin, N., Goodwin, P.H. and Guzman-Novoa, E., 2023. Varroa destructor and its impacts on honey bee biology. Frontiers in Bee Science, 1, p.1272937.
Connecting with ATTTA Specialists
If you’d like to connect with ATTTA specialists or learn more about our program, you can:
visit our website at https://www.perennia.ca/portfolio-items/honey-bees/
Email attta@perennia.ca