Chronic sublethal stress causes bee colony failure
Current bee population declines and colony failures are well documented yet poorly understood and no single
factor has been identified as a leading cause. The evidence is equivocal and puzzling: for instance, many
pathogens and parasites can be found in both failing and surviving colonies and field pesticide exposure is
typically sublethal. Here, we investigate how these results can be due to sublethal stress impairing colony
function. We mathematically modelled stress on individual bees which impairs colony function and found
how positive density dependence can cause multiple dynamic outcomes: some colonies fail while others
thrive. We then exposed bumblebee colonies to sublethal levels of a neonicotinoid pesticide. The dynamics
of colony failure, which we observed, were most accurately described by our model. We argue that our
model can explain the enigmatic aspects of bee colony failures, highlighting an important role for sublethal
stress in colony declines.