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Bees, undercrowding & the Allee effect

IMG_2665Back when I was a young and carefree student, I was occasionally to be found (only after the library had closed, obviously) in one of the local nightclubs. Even in sleepy Exeter, there was always a ‘hot’ place to be, which changed on a regular basis as clubs came in and out of favour.

Recently, I’ve been reminiscing about those heady pre-fatherhood days, as I’ve been reading about the Allee effect and its significance for honeybee colonies.

A nightclub can only thrive when busy – we go to clubs to dance (more fun in a full, noisy room) and ‘make new friends’ (much easier in a crowd, so I’m told) – if the club’s too empty even regulars stop going and it quickly closes down.

In the same vein, Warder Allee, an ecologist, proposed that “undercrowding” can limit population growth in the natural world by, for example, making it too hard for an individual to find a partner for cooperative hunting or even a mate.

So how does this relate to bees?

First reported in 2006, there is a now large body of research into so-called ‘Colony Collapse Disorder’ and its possible causes. A strong consensus has built that the phenomenon is the result of a combination of stresses on honeybee colonies. These are typically thought to include Nosema, Varroa and virus infestations, exposure to agricultural pesticides and unnatural experiences such as high hive densities, poor nutrition and regular long-distance movement.

New research, published in the scientific journal PLOS One, sheds further light on the issue and, in my opinion, strengthens the existing hypothesis.

Brian Dennis, professor at the University of Idaho, and William Kemp of the US Department of Agriculture, mathematically modelled colony growth and collapse and showed that population size could be the most important factor.

Dennis and Kemp appear to have confirmed a theory first proposed by Lee Dai, then a physics graduate student at MIT, who discovered in 2012 that when yeast colonies reach a small enough size (which they termed the tipping point), complete collapse is inevitable. Field trials in 2013 confirmed that this effect also occurred in honeybee colonies.

Dennis and Kemp link this with the Allee effect by noting that a honeybee colony functions almost as a single cooperative organism. Sufficient adult workers are required to tend the developing brood, so have a positive feedback loop whereby more adult bees in the hive allows recruitment of more adult workers and an increase in hive population (limited by the rate at which the queen can lay eggs).

Conversely, there is a minimum number of adult bees required, below which mortality is greater than recruitment and the colony quickly collapses. In ordinary conditions, this so-called ‘critical hive size’ is small – a population with as few as 1,000 bees (far less than the 10,000 bees in a typical commercial bee package) can thrive.

Importantly, Dennis and Kemp found that external stressors (including reduced communications or foraging abilities, reduced egg laying, increased stage specific developmental times, increased mortality or decreased cooperative hive protection) can massively raise the critical hive size to above that of a typical colony, resulting in the rapid collapse of previously strong colonies.

Bees, just like students, like a crowd and an “undercrowded” hive will collapse just as quickly as an out of favour nightclub.

VitaFeed Gold is a great way to nourish and strengthen colonies suffering from all kinds of stresses and – unlike the tipple in nightclubs – your bees will still feel great the next day!

Sebastian Owen

Commercial Development Manager at Vita

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