The Parasitic Threat to the Humble Honey Bee

Parasites, those devilish creatures which leech nutrients at their host’s expense, may be posing yet another threat to honey bees. The proposed perpetrator is the phorid fly Apocephalus borealis, a small parasite of the Phoridae family. As a member of the Apocephalus genus, they are best known for parasitizing ants, though there are less well-studied examples of A.borealis, in particular, parasitizing bees, wasps and beetles. In a paper by Core et al (2012) the first potential signs of honey bees as a new host source for the phorid fly and the unfortunate harm this may cause was identified.

               Honey bees are renowned for their monumental service to the ecosystem by pollination. A multitude of fruits and vegetables consumed by humans are pollinated by honey bees, and whilst they are not alone in their role, they are most definitely considered one of the best. Their loss risking large disturbances to humanities agricultural industry. This damage to honey bee populations has been termed colony collapse disorder (CCD), which is when a mass of worker bees abandon the hive leaving only a small minority which cannot sustain themselves and therefore die. The possible reasons for CCD are many, including causes such as malnutrition or pesticides, but the exact reason(s) remain unknown.

               It is, therefore, with mixed feelings that we come to find out that A.borealis has as of late been parasitizing honey bees. Mixed because on the one hand whilst we may celebrate that we have discovered this parasitism early in its emergence, and thus stand a better chance of getting ahead of the issue, we have also encountered a new obstacle for the helpful honey bee of which we know little about. The most curious discovery which came about was the behaviour of infected honey bees. From a nearby observation hive it was seen that stranded worker bees would be attracted to light fixtures and fly around them in disoriented patterns, regardless of weather conditions. It was further noticed that honey bees would abandon their colonies at night, a behaviour which greatly increased the chance of infection by A.borealis, where as many as 91% of honey bees in September/October that left the hive at night were parasitized. Upon leaving the hive, stranded bee’s would then show little activity for 24 hours before they finally passed away. Further corroboration of these observations can be observed by the increase in CCD losses around the same time that the risk of parasitism by A.borealis peaks in September/October.

               In trying to understand the cause of these odd behaviours which lead to CCD, a number of questions and problems are to be expected. For one, it is unknown when the shift in hosts from bumble bees to honey bees occurred so we do not know how much further the parasite will develop with its new host. A problem of concern due to the far larger density in which honey bees live compared to bumble bees, present a far greater opportunity for aggressive virulence. It is also unknown what the driving force is behind the detrimental honey bee behaviours. One possibility is that the A.borealis is directly causing a change to the bee’s sensitivity to light. Alternatively, hive abandonment may be caused by the hive itself. If the hive is aware of an infected worker bee the healthy individuals may show increased aggression, causing the infected to leave so they cannot infect more of the colony. All these questions call out for a resolution if we are ever to attain a sense of stability around the honey bee population we rely on so much.

Journal reference: Core, A., Runckel, C., Ivers, J., Quock, C., Siapno, T., DeNault, S., Brown, B., DeRisi, J., Smith, C.D. and Hafernik, J., 2012. A new threat to honey bees, the parasitic phorid fly Apocephalus borealis. PLoS One, 7(1), p.e29639.

If you’re interested in learning more about bee’s and colony collapse, take a look at this video on ‘The Death Of Bees’ by Kurzgesagt:

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