Drifting in honeybees

During previous research on deformed wing virus (DWV) biology and its transmission by Varroa I’ve moved known Varroa-free colonies (sourced from a region of the UK which the mite has yet to reach and maintained totally mite-free) into apiaries in the countryside. Within 2-3 weeks Varroa was detectable in sealed brood, showing that mite infestation occurs very readily. I know other researchers who have made very similar observations. Where do these mites come from?

They’re not all ‘your’ bees

The obvious source would be the phoretic mites transported on workers ‘drifting’ from nearby infested colonies, or on drones which are known to travel quite long distances and may be accepted by almost any colony. If you want to see how frequent this is try marking a few dozen drones with a dab of paint. To avoid confusion use the colour used to mark queens next year. There are unlikely to be 4+ year old queens in the apiary and the drones will all perish before the end of the current season. Over the next few days and weeks the drones will appear in adjacent colonies, and some will likely leave the apiary and be accepted in your neighbours colonies.

How to encourage drifting ...

How to encourage drifting …

Beekeepers are usually aware that colonies at the ends of rows often ‘accumulate’ bees that have drifted when returning to the hive. In shared association apiaries some crafty beekeepers will site their colonies at the ends of rows to take advantage of the ‘generosity’ of other colonies. However, many beekeepers probably do not appreciate the extent to which drifting occurs. Pfeiffer and Crailsheim (1998) report that 13-42% of the population of a colony are ‘alien’ i.e. have drifted from adjacent hives, depending upon the time of season. Remember that drifting occurs in both directions simultaneously, so the overall numbers of bees in a colony may not be adversely affected (or boosted). In other studies Sekulja and colleagues (2014) showed that ~1% of marked bees drifted between colonies over a three day observation window. Interestingly, American foulbrood (AFB) infected bees drifted slightly more than uninfected bees. Spread of foulbroods during drifting is one reason the bee inspectors check nearby apiaries when there is an outbreak. These studies were all on workers where drifting primarily occurs during orientation flights before the bees become foragers. Drones drift two to three times more than workers (Free, 1958).

The likelihood of drifting must be closely related to the separation of hives and apiaries. Although workers will forage up to 2-3 miles from the hive I suspect the proportion of bees that drift this distance is extremely small. However, unless you’re very isolated I expect there are other apiaries within a mile or so of your own. Drones are known to fly up to about five miles to reach drone congregation areas for queen mating and are accepted by all colonies. I’ve regularly found drones appearing in (relatively) isolated mini-nucs. I’m not aware of studies that have formally tested drifting between apiaries (though it is reported in passing in the Sekulja et al., 2014 paper cited above).

Consequences of drifting

So, your hives probably contain workers and drones from other nearby colonies, and you can only really be sure that they’re all “your” bees if you live – as the sole beekeeper – on an isolated island. Not only does your neighbour generously exchange bees with you, he or she also kindly shares the phoretic mites those bees are carrying, the viral payload the bees and mites are infected with and – if you’re really unlucky – the Paenibacillus larvae spores responsible for causing AFB infection (and vice versa of course).

There are lessons here that should inform the way we conduct our integrated pest management to maintain healthy colonies. 

This post provides background information for an article (“Viruses and Varroa: Using our current controls more effectively” by David Evans, Fiona Highet and Alan Bowman) in the December 2015 issue of Scottish Beekeeper, the monthly magazine for members of the Scottish Beekeepers Association.

More later …

 

8 thoughts on “Drifting in honeybees

  1. Emily

    Interesting, and worrying that American foulbrood (AFB) infected bees drifted slightly more than uninfected bees.

    In this interview with Prof Tom Seeley: https://drive.google.com/file/d/0B-Jxfu3q18ocelBwRmJxeWdvZUU/view – he talks about his current research into wild populations of honey bees in an isolated New York state forest. The wild bees are surviving despite receiving no varroa treatments and Professor Seeley believes reasons for this may include wide spacing between colonies (as well as small nest sizes & frequent swarming). I have to admit for reasons of convenience and space restrictions my colonies are kept close together, but unfortunately this is not great from a disease point of view.

    Reply
    1. David Post author

      I seem to remember that the foulbrood-infected bees drifted more but that the statistical significance of the difference was, at best, weak. In small apiaries colonies are often situated so close together that they could be considered a multi-queened super-colony as far as disease and drifting are concerned.
      In a large, shared, association apiary I would sometimes find marked drones from colonies some distance away (perhaps where they’d been practising marking for queens). Under these circumstances what always worried me was the beekeeper who forgot (or chose not) to use any autumn mite treatments, those that brought colonies back from the heather (these always arrive back late in the season and, by definition, haven’t been treated as they’ve been busy collecting nectar from the heather … or slowly starving in the wind and rain on the moor) and the few swarms that got hived on site, but were perhaps collected elsewhere. Fortunately we never had any major problems, but I thought then that there may be better ways to tackle mites … I’ll post more on this in the near future.

      Reply
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  6. ralph

    “Drones are known to fly up to about five miles to reach drone congregation areas for queen mating and are accepted by all colonies.” What are your references for this statement of 5 miles?

    Reply
    1. David Post author

      Ruttner and Ruttner did much of the early work on this – most of the papers are in Apidologie and are in German. Try here for starters. In addition, you could look at ‘Drone Congregation Areas’ by C. Collison in Bee Culture, Sep 2008. Finally, though this covers the distances the queen flies to DCA’s, you could have a look at work on using microsatellite analysis (Jensen et al., 2005 Conservation Genetics 6:527-537) which showed that the maximal mating distance was 15 km, that 90% occurs within 7.5 km and that 50% occurred with 2.5 km. Both virgin queens and drones may fly considerable distances for mating … presumably a means of overcoming inbreeding when colonies are at a low density.

      Reply

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