Wednesday, April 8, 2015

What stimulates swarming, and what does it mean for keeping your bees? Another Talk by Dr. David Gilley

I apologize that I've put off sharing my notes on Dr. David Gilley's second lecture at my last beekeeping club meeting. (You can check out my notes on his first lecture, which was about pheromones and waggle-dancing, if you like.) The truth is that I started this post ages ago, but then Blogger glitched, and I lost everything I'd written. Then I got so distracted by getting my tax stuff together and whatnot. Things are back on track, though, so I figured I'd give this one more try, especially since Dr. Gilley, who is a behavioral scientist at William Paterson University gave such an interesting talk on a subject that concerns us all this time of year -- SWARMING!

Without further ado, here are my notes.

Review of Swarming as Part of Reproduction

Four Stages of Reproductive Fission in the Honey Bee Colony

Stage 1: Preparation for Fission
  • Queen rearing. Queens are reared so that the remaining colony (and/or any after-swarms) will have a queen.
  • Worker population increases. The worker population increases. There need to be enough workers for both the swarm and the remaining colony.
  • Nectar hoarding commences to ensure a ready supply of resources for the new queen and her colony.
  • Physiological changes in mother queen. The mother queen undergoes physiological changes such as slimming down so that she can fly with the swarm and vision changes so that her eyes get a workout
Stage 2: Swarming
  • Nest departure. Just before the new queens are capped, the mother queen and a large portion of the colony depart from the nest and fly off. They become the daughter colony.
  • Bivouac clustering. The swarm has no home, so they cluster somewhere until scouts can find an acceptable new home for the swarm.
Stage 3. Daughter Colony Established
  • Scouting. Scouts are dispatched from the swarm to find a home for the new swarm. 
  • Decision-making. Scouts report their findings to the swarm. Collectively, the bees decide which home they want.
  • Bivouac departure. Once the swarm has made a decision, they depart en masse to their new home, and set up shop their.
Stage 4. Parent Colony Reconstituted
  • Queen Elimination. The first virgin queen to emerge kills the other queens in their queen cells to eliminate competition.
  • (Secondary Swarming). If the colony is very large, secondary swarming may occur. In this step, additional swarms may be cast. Virgin queens will fly with them. Secondary swarms help speed up queen elimination.
  •  Queen mating. Once she has eliminated her rivals, the virgin queen will take a series of mating flights and begin laying eggs.

Proximate Causes of Swarming

  • In order to better understand why bees swarm, we need to identify proximate and ultimate causes of swarming.
  • Proximate causation is a mechanistic kind of causation. It is the event that is immediately responsible for causing something to happen. Ultimate causation is an evolutionary question that addresses fitness adaptive arguments.
  • Example: Male stickleback fish have very red bellies. The male stickleback is also highly territorial and will attack all other males entering his territory. Why does the male attack? There are both proximal and ultimate causes for this aggression.

    Proximal cause:
     A male sees the red belly of an intruding male and attacks. The red belly of the intruding male is a sign stimulus that causes releases aggression in the male defending its territory.

    Ultimate cause:
     By chasing away intruding males, a male decreases the chances that eggs laid in his nesting territory will be fertilized by another male.
  • With regard to bees and swarming, beekeepers need to be able to identify Stage 1, the preparation for reproductive fission if they want to prevent swarming. The ultimate causes associated with the events of this stage are pretty obvious. If beekeepers want to get ahead of the game, they need to understand the proximal causes associated with the events of preparing for reproductive fission.
Ultimate causes for Stage 1 of Reproductive Fission

Seasonal Physiological Changes

  • During the spring, many animals experience seasonal physiological changes as a result of changes in day length and temperature. These environmental cues (in the form of longer dyas and warmer temperatures) cause gene expression changes in neurosecretory cells of the brain. These changes cause hormonal changes in the production of various hormones, which leads to physiologic changes. For example, as days grow longer in spring, the physiognomy of male birds changes as their testes begin to grown and produce more sperm. These physiologic changes lead to behavioral changes. Again taking the example of birds, in spring, they start defending their territory, attracting mates, and building nests. Nest building and egg laying are the end result in a chain reaction of events that began with a change in day length. If you wanted to prevent birds from reproducing, you could simply manipulate the amount of light they receive.
  • The advent of spring also causes seasonal physiological changes in bee colonies. The image below shows this sequence cues and events. 

In the chart above, 7 hypotheses have been identified as proximal causes for swarming. Note that these causes are not exclusive (i.e., rather than being stand-alone causes, they likely work in tandem to cause swarming). These proximal causes are: 
  1. Photoperiod (longer days)
  2. Warmer temperatures
  3. Nectar availability
  4. Increased worker density as a result of more eggs having been laid over time
  5. Increased comb congestion due to increased worker density
  6. A younger population as a result of increased egg laying
  7. Decreased queen pheromone distribution. As the population gets larger, the queen is not able to disperse her pheromone as effectively.

Review of Literature

The evidence for causal links between colony-level cues and swarm preparation has been summarized by Grozinger et al. (2014) in a review of literature. The review indicated that a number of cues can be correlated with swarming events. However, no one single cue causes swarming. Highlights of this review are as follows:

Increased Worker Density

  • Colonies began constructing queen cells when the population density exceeded 2.3 workers/ml
  • The number of queen cell that were constructed correlated with worker density. So the greater worker density resulted in greater numbers of queen cells.

Increased Comb Congestion
  • When more than 90% of the brood comb was occupied, workers began queen rearing.
  • Colonies with congested brood comb swarmed earlier than colonies with less congested brood comb.
  • Even though colonies with congested brood comb swarmed earlier, colonies with uncongested brood comb will sometimes swarm. So congestion is not necessary for swarming. 
Younger Population
  • Colonies that swarm have younger bees overall.
  • However, simply shaking a lot of younger bees into a hive will not trigger swarming.
Decreased Queen Pheromone
  • When the colony is congested, the queen does not spend as much time in the outer edges of the brood nest.
  • It's possible to reduce queen cell construction by applying QMP (queen mandibular pheromone) on the edges of combs.
  • In large colonies, fewer workers have detectable levels of QMP.
  • In congested colonies, swarming can be delayed by applying QMP.
Swarm Control through Nectar Management

Note, at this point, I'm going to stop sharing notes and simply share what happened along with my own musings.

Dr. Seeley passed out copies of an article written by Walt Wright on the subject of nectar management (i.e., checkerboarding), which we all read and discussed. You can read a number of articles by Mr. Wright online. These articles include a description of checkerboarding, including what it is and how it is done.

Checkerboarding is a technique that prevents swarming in Langstroth hives by providing empty space above the brood nest. This is done by alternating empty frames with full frames of honey in boxes above the brood nest. The timing of checkerboarding is also critical since it needs to be done before the first hardwood blooms. Here is an easy-to-read synopsis of it.

Since checkerboarding is a practice that's really designed for Langs, I won't go into it in much detail here. However, I do think it's interesting to think about how it might be applied in a TBH. I've seen TBH management diagrams that recommend alternating full and empty bars in the honey area of a TBH during a strong flow. However, don't think that this encourages the kind of massive comb-building that checkerboarding does.

What do you think about it? Have any thoughts about how it could be applied in a TBH setting?

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