> 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. 

>Colony loss monitoring does not show a correlation with the use pattern of pesticides. In Canada, where most honey production is from bees foraging on canola, hive numbers and productivity have increased steadily since neonicotinoid-treated canola seed were introduced (Canadian Honey Council 2009; Statistics Canada 2012). In contrast, high colony losses have occurred on Vancouver Island, where agrochemical use is virtually non-existent. Neonicotinoids are used in Australia, where honey bee losses have not occurred. 

> The bee experts who attended the workshop: Troy Anderson, Tjeerd Blacqui`ere, Jerry Bromenshenk, Diana Cox-Foster, James Cresswell, Chris Cutler, Galen Dively, Frank Drummond, David Epstein, Richard Fell, Gerald Hayes, Josephine Johnson, Christian Maus, Richard Rogers, Melinda Rostal, Cynthia Scott- Dupree, Thomas Steeger, Helen Thompson, and Geoffrey Williams. Special thanks to Glenn Suter, Susan Cormier, and Erica Fleishman for their expertise in causal analysis. 

Staveley, J. P., Law, S. A., Fairbrother, A., & Menzie, C. A. (2014). A Causal Analysis of Observed Declines in Managed Honey Bees (Apis mellifera). Human and Ecological Risk Assessment: An International Journal, 20(2), 566-591.

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