Allee effects and colony collapse disorder in honey bees

Authors: DENNIS, BRIAN - University Of Idaho; Kemp, William - Bill

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/11/2014
Publication Date: 1/10/2015
Citation: Dennis, B., Kemp, W.P. 2015. Allee effects and colony collapse disorder in honey bees [abstract]. 2015 Joint Mathematics Meetings. Paper No. 1106-92-1258.

Interpretive Summary: Honey bees, in addition to generating a wide range of hive products for human consumption, provide irreplaceable pollination services to agricultural and natural ecosystems. Although the domestication of the honey bee is closely connected to the evolution of food-based socio-economic systems in many cultures throughout the world, in current economic terms, and in the U.S. alone, the estimated wholesale value of honey, more than $317 million dollars in 2013, pales in comparison to aggregate estimated annual value of pollination services, variously valued at $11-15 billion. Yet, it is generally agreed that domestic and feral honey bees in North America are in crisis due to a variety of stressors including pathogens, parasites, the rigors of migratory beekeeping associated with pollination of crops like California almonds, as well as environmental factors such an forage availability and xenobiotics. Additionally, one third to one half of the 30% average annual wintering losses experienced by self-reporting U.S. beekeepers has been associated with Colony Collapse Disorder. Characterized by the mysterious loss of hive-level viability, CCD is spatially widespread, and although numerous inimical factors have been implicated, no single cause has gained consensus. Herein, we propose a mathematical model to quantify the hypothesis that a major ultimate cause of Colony Collapse Disorder (CCD) in honey bees is the presence of an Allee effect – a phenomenon associated with conservation biology, and small populations - in the growth dynamics of honey bee colonies. In the model, both recruitment of adult bees as well as mortality of adult bees have substantial social components, with recruitment enhanced and mortality reduced by additional adult bee numbers. The result is an Allee effect, a net per-individual rate of hive increase that increases as a function of adult bee numbers. The Allee effect creates a lower critical size in adult bee numbers below which mortality is greater than recruitment, with ensuing loss of viability of the hive. Under ordinary and favorable environmental circumstances, the critical size is low, and hives remain large, sending off viably-sized swarms (naturally or through beekeeping management) when hive numbers approach an upper stable equilibrium size. However, both the critical size and the upper stable size depend on several many parameters related to demographic rates their and enhancement by bee sociality. The model suggests that multiple proximal causes, among them pesticides, mites, pathogens, and climate change, working singly or in combinations, could trigger CCD by exacerbating the Allee effect.

Technical Abstract: We propose a mathematical model to quantify the hypothesis that a major ultimate cause of Colony Collapse Disorder (CCD) in honey bees is the presence of an Allee effect in the growth dynamics of honey bee colonies. In the model, both recruitment of adult bees as well as mortality of adult bees have substantial social components, with recruitment enhanced and mortality reduced by additional adult bee numbers. The result is an Allee effect, a net per-individual rate of hive increase that increases as a function of adult bee numbers. The Allee effect creates a lower critical size in adult bee numbers below which mortality is greater than recruitment, with ensuing loss of viability of the hive. Under ordinary and favorable environmental circumstances, the critical size is low, and hives remain large, sending off viably-sized swarms (naturally or through beekeeping management) when hive numbers approach an upper stable equilibrium size. However, both the critical size and the upper stable size depend on many parameters related to demographic rates their and enhancement by bee sociality. The model suggests that multiple proximal causes, among them pesticides, mites, pathogens, and climate change, working singly or in combinations, could trigger CCD by exacerbating the Allee effect.