Asian Giant Hornet (Vespa mandarinia)

Thursday 19 November 2020

Last week we looked at the host parasite relationship between the European honey bee and the Varroa mite.  One of the reasons the Varroa mite is so damaging to our honey bees is that these two organisms did not evolve together and therefore our bees, as a naïve host, have not developed sufficient mechanisms of defense.  There are other examples of honey bee pests which threaten our bees for the very same reason.  Let us investigate a couple of high profile honey bee pests which we need to keep an eye on….

Asian Giant Hornet (Vespa mandarinia)

Murder hornets make a great news headline and the media has certainly reported on this new invasive species to Canada.  A quick Google News search returned almost 100 000 hits on the search words “Canada Murder Hornets.”  We have discussed this previously and  “WHAT’S THE BUZZ ABOUT THE ASIAN GIANT HORNET?”  contains all the facts needed for our regions beekeepers.

Asian Giant Hornet. Photo: B.C. Ministry of Agriculture

If we look at their behavior, the Asian giant hornet is a very impressive predator.  The strategies used by the Asian giant hornet are fascinating to learn about but devastating to honey bees.  A large colony of Asian giant hornets sends out scouts to locate the beehive.  These individual scouts will place a marker pheromone, or chemical scent, which allows its hive-mates to also find this rich food source.  Now attracted to this location, the growing number of hornets may be able to overwhelm the honey bees to the point at which they will abscond.  This leaves young bees, larva and honey which the hornets will feast on for the following few days.

Asian honey bees (Apis cerana) can detect and react to the marker pheromones.  They set up defenses to protect themselves from these hornet attacks and become more vigilant in guarding the hive entrance.  The Asian honey bees guarding the entrance prepare to ‘heat ball’ and kill hornets attempting to enter the hive.  So the Asian honey bee has developed strategies to defend against these pheromonal attack strategies.  The European honey bee (Apis mellifera) has no such defenses and very little reaction to the marker pheromones leaving it more vulnerable to Asian giant hornet attacks.


Tropilaelaps mite

Another threat from Asia, the Tropilaelaps mite may be following the same route of spread as did the Varroa mite.  Its life cycle is similar but it will outcompete the Varroa mite in the same hive.  For this and other reasons the Tropilaelaps mite may be an even bigger threat!   They have a faster reproductive cycle than the Varroa mite.  Their greater genetic diversity, as mating doesn’t result from inbreeding, may enable quicker adaptation.  For this reason, plus a relatively short phoretic phase, they may more quickly develop acaricide resistance.  Their feeding behavior is also more damaging to larva resulting in malformation of adult bees.  If not bad enough, like the Varroa mite, the Tropilaelaps mite, is a vector for honey bee viruses.

Distribution Tropilaelaps ssp. Source: World Honey Bee Health

Our honey bees (Apis mellifera) lacks the behavioral defense strategies, such as the ability to remove mites through mutual grooming, to manage a Tropilaelaps infestation.  The emerging threat of Tropilaelaps mite to our honey bees is worth informing ourselves about now!


So, here we have additional examples of threats to our honey bees from a pest for which they have no innate defenses.  A pattern seems to be emerging.  We are moving bees to areas where they lack sufficient defenses against indigenous pests and diseases.  Ongoing migration of our honey bees for pollination, queen sales or other inadvertent transportation spreads these novel pathogens to naïve colonies.  This has occurred in the case of Varroa mite, spreading this parasite around the globe.  It has been stated that the greatest threat to honey bees is additional stress from diseases and pests as a result of the movement of bees (See blog # 23!).  For these pests, parasites and diseases, a novel host may be relatively defenseless.  But the difficulties for these disease organisms to living in and adapting to a new geographic region often limit their spread.  One of these difficulties is a different climate and we hope that emerging pests will not survive our cold winters.  This suggestion has been put forward for the Small Hive Beatle, Tropilaelaps mite and the Asian Giant hornet.  We also see that these organisms are showing adaptability and, as will all animals, have a strong need to survive which drives adaptation.  Their ability to successfully survive in our region is yet to be determined.

We need to be vigilant and do the work, research and preparations for these emerging threats.  Let’s follow the old axiom first said by Benjamin Disraeli, “I am prepared for the worst, but hope for the best”.  Or perhaps even better stated by Maya Angelou, “Hoping for the best, prepared for the worst, and unsurprised by anything in between.”


Additional reading

Beverly McClenaghan, Marcel Schlaf, Megan Geddes, Joshua Mazza, Grace Pitman, Kaileigh McCallum, Samuel Rawluk, Karen Hand & Gard W. Otis (2019) Behavioral responses of honey bees, Apiscerana and Apismellifera, to Vespamandarinia marking and alarm pheromones, Journal of Apicultural Research, 58:1, 141-148, DOI: 10.1080/00218839.2018.1494917

Gengping Zhu, Javier Gutierrez Illan, Chris Looney, David W. Crowder (2020) Assessing the ecological niche and invasion potential of the Asian giant hornet, Proceedings of the National Academy of Sciences Oct 2020, 117 (40) 24646-24648; DOI: 10.1073/pnas.2011441117

Panuwan Chantawannakul, Samuel Ramsey, Dennis vanEngelsdorp, Kitiphong Khongphinitbunjong, Patcharin Phokasem (2018) Tropilaelaps mite: an emerging threat to European honey bee, Current Opinion in Insect Science, Volume 26,Pages 69-75, ISSN 2214-5745. 

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