Varroa mites (Varroa destructor) are a severe pest of
honey bees (Apis mellifera), feeding on their bodily fluids and
transmitting various pathogens. The management of Varroa mites relies heavily
on chemical treatments despite an increasing concern for miticide efficacy.
Therefore, there is a need to develop more treatment options so that an
integrated pest management approach can be continued. An improved understanding
of the chemical ecology between Varroa mites and honey bees may be the first
step in reducing the reliance on miticides. In this week’s blog, we will
discuss a study done by a team at Acadia University in the labs of Dr. Kirk
Hillier, Dr. Dave Shutler, and Dr. Nicoletta Faraone, which investigated how
volatiles of honey bees elicit various behavioural responses.
A Review of “Locomotion behavioural responses of Varroa
destructor exposed to western honey bee (Apis mellifera) semiochemicals”
It is important to study the chemical ecology between honey bees and their pests, especially that of Varroa mites which pose a severe threat to the honey bee industry. Unlike honey bees, Varroa mites do not have eyes, and depend on touch and smell to seek out a host. Their ability to detect honey bee colony volatiles is very important in their success at completing their life cycle. Michael Light, first author and part of the research team for this recent study, describes “With increasing reports of mite resistance to current chemical treatments used in apiculture, beekeepers need to find additional tools to manage mite infestations. Varroa mites are highly tuned to volatile chemicals that are released by adult and larval honey bees in colonies. With a better understanding of the chemical ecology of Varroa mites, we can work towards new methods to interrupt mite life cycles.”
The study (Light et al., 2023) required mature Varroa
mites collected from honey bees. They used honey bee colonies with high Varroa
mite infestations and used the queen-trapping technique to remove mites from a
colony for testing. The queen-trapping technique involves using a drone brood
frame and frame cages to trap a queen for 2-weeks, so she exclusively lays drone
brood, and creates a gap in the honey bee brood cycle. This ensures that Varroa
mites infest these drone brood in sufficient numbers. Once drone brood had been
mostly capped, the drone brood frame was removed and kept in an environmental
chamber to rear to adulthood. Then adult drones were transferred to cages and
Varroa mites were collected using a paintbrush and an aspirator.
This study aimed to test volatile compounds and mixtures
that were previously detected in honey bee colonies and their effects on
behaviour of Varroa mites in a controlled arena. As described by Michael Light,
“Honey bee colonies can contain an enormous variety of volatiles that vary from
one colony to the next. There are several approaches to collecting volatiles
from honey bee colonies. One approach to collect volatiles involves trapping
these compounds using a closed-loop system which involves enclosing a part of a
honey bee colony (e.g., a brood frame) so that air can be pumped over it and
then trapped using a special type of polymer adsorbent cartridge. Trapped
volatiles can then be released from these adsorbent cartridges for analysis.”
The researchers observed and described the movement of Varroa mites in response to honey bee colony volatiles. “These behavioural tests were done in an environmentally controlled chamber under low light conditions so as to mimic a honey bee colony environment. We placed single live Varroa mites each in their own enclosure, which contained filter paper treated with a known amount of a honey bee-related volatile and filmed their behaviour with a camcorder.”
The results of the study suggest that Varroa mites have different levels of behavioural responses to different volatiles at different concentrations. Michael Light states that “Varroa mites responded significantly to some of these compounds at the lowest concentration, suggesting that they may be important to the mite life cycle.” Additionally, “the synthetic Varroa sex pheromone mixture may be important to adult Varroa mites when presented in this particular assay design, and this is important as it was never previously tested against adult mites to our knowledge.” Finally, “mite behaviour towards synthetic brood pheromone and Varroa sex pheromone mixtures suggests that single volatile compounds are equally important as their respective synthetic mixture.”
This team of researchers has benefited the honey bee
industry by improving our understanding of the chemical ecology between Varroa
mites and honey bees. Additionally, they have created a
baseline for future research, including the potential to identify repellent
compounds of Varroa mites using this assay, and, overall, working towards
improving mite management.
Light, M.,
Shutler, D., Faraone, N., Cutler, G.C. and Hillier, N.K., 2023. Locomotion
behavioural responses of Varroa destructor exposed to western honey bee
(Apis mellifera) semiochemicals. Journal of Pest Science, pp.1-10.
Light, M.
2023. Interview by Kayla Gaudet.
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 abyers@perennia.ca