What You Need to Know About Australia’s Latest Unwanted Arrival: Braula Fly
Australian beekeepers are currently grappling with a Varroa destructor incursion and making headway in elimination of the honey bee parasite. However, surveillance as part of the incursion response has unveiled another unwelcome visitor – braula fly. It’s not yet been detected in New Zealand, but Dave Black has some experience with the wingless fly that lives on honey bees and just got that bit closer to our shores. He explains how Aussies aren’t best pleased about their most recent biosecurity incursion not for the danger it might be responsible for inside a hive, but because it represents a failure of process.
There’s much more in a hive than ’bees. When I was a learner beekeeper in England, braula fly was a rare but not unexpected visitor to the local apiaries. At the time (1994-ish) the job was to learn the difference between braula, the bee ‘louse’, which we had seen, and the new nuisance, the eight-legged varroa mite. News has now reached us that in August, the state of Victoria’s routine mite surveillance detected braula in local hives destined for almond pollination. They had obviously learnt the difference.
This wasn’t the first time for Victoria; braula has inhabited Tasmanian colonies for almost a century and has been found and eliminated in Victoria several times. This time, unfortunately, infected hives, perhaps illegally, ended up in NSW in September where a beekeeper picked it up. NSW is currently wondering if it’s even worthwhile continuing to regulate braula at all. I wouldn’t mind being a fly on the wall there…
Braula coeca Nitsch, to give its full and fancy name, has been found in beehives almost everywhere in the world where there are honey bees. We should call it Braula sp (species) or refer to them as Braulidae really, because there is a lot of debate about what particular species is where. Appropriately there are even two species of Megabraula (!) for the largest honey bee, Apis laboriosa. Not long after my first encounter with braula in the UK John Dobson (with some help from my local Bee Inspector, James Morton) published an article noting that there were in fact two different UK species, B coeca and B. schmitzi, but it didn’t make a difference in the apiary. There are seven species identified so far.
The bee louse was first reported to science by Reaumur in 1740. Yes, that Reaumur… René-Antoine Ferchault de Réaumur was a Parisian physicist and entomologist who also invented a temperature scale about the same time as Mr Fahrenheit (in 1724), and Mr Celsius (1742). Braula was formally named by a German zoologist Christian Nitzsch in 1818. It isn’t a louse, zoologically speaking, but a six-legged, wingless fly from the insect order Diptera, perhaps one of the most diverse and ecologically successful groups on earth. Its closest relatives are the Drosophila flies cherished by geneticists.
Studying a single type of fly is a pretty niche occupation, particularly when it’s very small, doesn’t seem to have any economic consequences, and lives in a nest full of stinging insects. Understandably it rarely has much written about it, and what there is mostly dates from the 1920s-1940s. The experts describe it as an inquiline (Latin in the sense of a lodger or tenant) and sometimes a ‘kleptoparasite’, to mean that its ‘parasitism’ is facilitated by theft. If beekeepers around the world note its existence at all, it is with that collective shrug, meh!
How Do You Spot It?
That it turns up when varroa sampling is not surprising, it’s just that most of the time people don’t look too closely at the brown dots they are counting. Braula are ‘lumpy’ on a sticky board, rather than a flat scale. Old treatments for braula include repeated smoking (hives or caged queens) with tobacco, or thymol, or camphor, so they would fall off, an exercise only marginally more effective than picking them off your queen one-by-one with a sticky stick (sticky with honey obviously).
The new treatments (pyrethroids) used for mite drop tests have a similar, but less lethal, effect on braula, dropping them onto the sticky boards, although vapours might be more effective. I have a vague memory of Folbex (strips containing 370mg weight-for-weight bromopropylate we burned to control acarine) coincidentally ‘doing’ the braula, but Folbex has been banned for many years thank goodness. There is evidence that several of the current varroa treatments have reduced the frequency of braula finds over time.
The adult flies ride around on bees stealing food directly from the mouth as the host bee feeds or feeds others. They have a distinct preference for laying queens, rarely virgins, but occasionally using drones and workers. Usually there may be one or perhaps two on a bee, but queens can sometimes be found that are plagued with lots of them, reports counting around 30 on a single queen are not unusual. Early accounts from the turn of the 20th century of several hundred per queen have been questioned, pointing to confusion between braula and pollen mites.
They’re also pretty good at not falling off. A study last year looked closely at the specially adapted claws that knit into the bee body hairs, yet when released allow them to move quite quickly and securely across waxed surfaces. It includes several action videos, scanning electron microscopic images, coloured confocal laser scanning images and drawings. The attachment is strong enough to allow lifting a bee by holding onto the braula! They will die if removed from the host after about six hours.
It is surprising they aren’t groomed off by the retinue of bees attending the queen; astonishingly the bees hardly notice them. Stephen Martin and Joe Bayfield have shown that’s because braula manage to use a chemical camouflage that either mimics the colony-specific ‘hive odour’, or (I think more likely) is acquired from the colony itself.
Life and Death
Braula have the same life-cycle stages as other insects and tend to follow the rhythm of the nectar flow. There appear to be twice as many males as females (the sexes are identical without a microscope). Reproduction starts in the spring and stops in the autumn; development to adult stage takes 10-20 days and is temperature-dependant. Adults over-winter in the hive, but their lifespan is unknown. Curiously, eggs can be found anywhere in the hive, but only the ones laid inside the closing cap of a honey cell will develop. Tiny translucent larvae hatch and tunnel along the wax under-surface, sealing themselves in tunnels formed from wax fragments. The tunnel grows with the larvae and cuts through adjacent cells and the visible ‘mesh’ or network of tiny burrows is characteristic of a braula infestation. The larva will pupate inside the tunnel for 1-3 days and must find an adult to feed from as soon as it emerges.
Having a small insect tunnelling through your comb isn’t ideal if you produce honeycomb for sale (with wax moth in mind it’s often frozen then thawed prior to sale), and some report infestations significant enough so that it may interfere with a queen’s ability to lay the brood nest. Nevertheless, braula has not proved to be a significant pest of honey bees for beekeepers, and is not likely to given current varroa management and normal commercial practice. New Zealand’s biosecurity advice was updated at the beginning of the year.
Dave Black is a commercial-beekeeper-turned-hobbyist, now working in the kiwifruit industry. He is a regular science writer providing commentary on “what the books don't tell you” via his Substack Beyond Bee Books, to which you can subscribe here.
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