A Causal Analysis of Observed Declines in Managed Honey Bees (Apis mellifera)

Abstract

The European honey bee (Apis mellifera) is a highly valuable, semi-free-ranging managed agricultural species. While the number of managed hives has been increasing, declines in overwinter survival, and the onset of colony collapse disorder in 2006, precipitated a large amount of research on bees' health in an effort to isolate the causative factors. A workshop was convened during which bee experts were introduced to a formal causal analysis approach to compare 39 candidate causes against specified criteria to evaluate their relationship to the reduced overwinter survivability observed since 2006 of commercial bees used in the California almond industry. Candidate causes were categorized as probable, possible, or unlikely; several candidate causes were categorized as indeterminate due to lack of information. Due to time limitations, a full causal analysis was not completed at the workshop. In this article, examples are provided to illustrate the process and provide preliminary findings, using three candidate causes. Varroa mites plus viruses were judged to be a “probable cause” of the reduced survival, while nutrient deficiency was judged to be a “possible cause.” Neonicotinoid pesticides were judged to be “unlikely” as the sole cause of this reduced survival, although they could possibly be a contributing factor.

The dose makes the poison: have “field realistic” rates of exposure of bees to neonicotinoid insecticides been overestimated in laboratory studies?

“…Similarly, using a formal causal analysis approach, Stavely et al (2014) concluded that "neonicotinoid pesticides were judged to be 'unlikely' as the sole cause of reduced overwinter survival of honey bee colonies, although they could possibly be a contributing factor".…”

Protocol for the in vitro rearing of honey bee (Apis mellifera L.) workers

“…Pesticides, nutrition, parasites, and/or diseases are thought to be major contributors to recent honey bee declines (Fairbrother, Purdy, Anderson, & Fell, 2014;National Agricultural Statistics Service, 2015;Neumann & Carreck, 2010;Staveley, Law, Fairbrother, & Menzie, 2014;Vanbergen et al, 2013). However, it is difficult to isolate the adverse impact of most of these stressors on honey bee health, particularly on immature honey bee health, because of the complexity associated with investigating multiple stressors simultaneously and the lack of quality, repeatable bioassays with which to do the work.…”

Risk factors associated with honey bee colony loss in apiaries in Galicia, NW Spain

“…One of the earliest and most studied hypotheses is related to the action of neonicotinoids and pheylpyrazole pesticides on bees (Smirle et al, 1984;Halm et al, 2006;Johnson et al, 2010;Staveley et al, 2014). As bees encounter these pesticides while foraging for pollen or nectar, comb-stored pollen could represent a chronic source of toxicity to bees (Thompson & Maus, 2007).…”