Colony Collapse Disorder: Why is it so difficult to study?

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1 Colony Collapse Disorder: Why is it so difficult to study? Dr. Gard Otis School of Environmental Sciences University of Guelph Guelph, ON, Canada Teacher & Researcher - apiculture, insect behaviour, field entomology) - bees, butterflies, birds) International development (Beekeeping in Vietnam)

2 Colony Collapse Disorder Sudden disappearance of adult bees from bee hives. First observed in winter of 2006/07 in USA; 1/3 of colonies died + many deaths in Canada & Europe. Problem has continued every winter since then. Search for the smoking gun BUT.. What if CCD is complex no simple cause?

3 Colony Collapse Disorder What are the possible causes?

4 Colony Collapse Disorder Scientists ask questions: What are the possible causes of CCD? - parasitic mites (2 species + genetic variants) - many viruses, some transmitted by mites - Nosema, a microscopic gut parasite (2 species) - sublethal effects of pesticides (dozens) - poor nutrition - stress (migrating colonies) - weakened immune system (combo of mites, pesticides, Nosema, nutrition, stress) - environmental conditions

5 Colony Collapse Disorder How do scientists answer questions? 1. Try to find associations between possible problems and dead colonies. Example: Collect bees from dead colonies, then analyze them for mites, viruses, pesticides, etc. 2. Set up a controlled experiment in which factors of interest ard set by the researcher Well designed, controlled experiments provide stronger evidence of cause of problem.

6 Colony Collapse Disorder How does one study this problem? Need to study whole colonies (not single bees) Honey bees always live in a society with thousands of sisters. Studying bees in lab may not be appropriate (social stimuli absent)

7 Colony Collapse Disorder Need replicates = multiple hives/treatment Max. apiary size = ~24 hives (for adequate resources) Need multiple apiaries increased variation; Limits # of variables that can be studied in one expt

8 Experimental set-up: 24 hives, 3 treatments Nosema absent N. ceranae N. ceranae Nosema absent Varroa No Varroa = high dose imidacloprid = low dose imidacloprid = control

9 Varroa mites Large problem worldwide; miticide resistance reduces ability to control mites. Varroa mites transmit viruses; Viruses are very difficult to control experimentally

10 Nosema intestinal parasite, similar to protozoan Nosema apis disease organism well known for more than 50 years. Nosema ceranae recently discovered disease organism in Apis mellifera Major cause of colony deaths in Spain; linked to colony deaths in USA Consequences of Nosema infection in a bee hive at end of winter Nosema spores as seen through microscope Cells in gut of honey bee infected with Nosema

11 Pesticides a never-ending problem Recent USA study of pesticides collected by bees while foraging (Mullin, CA et al., PLoS-ONE 5 (3), 19 March 2010 In pollen: 98 different insecticides herbicides, fungicides, and miticides(used to control Varroa mites Two chemicals at high conc. - miticide and fungicide - had no effect individually, but were deadly to bees when bees were treated with both at the same time.

12 Pesticides new evidence Neonicotinoid pesticides- block transmission of signals between nerves of insects. French study: sublethal doses of imidacloprid caused bees to be unable to orient back to their hives. Study in 2009: repeated low doses of neonicotinoid insecticides are much more lethal to insects than single higher doses times less insecticide was required to kill honey bees when it was applied continuously over several days.

13 Interesting new research 1. Bees fed a diet of many different types of pollen have more active immune systems than those fed only one type of pollen. * What are the consequences of large scale agriculture a single crop, few weeds? 2. Parasitic mites reduce immune system function * Colonies with large number of mites tend to have more diseases

14 Conclusions 1. So many variables can affect honey bees. 2. Some variables are difficult or impossible to control, so establishing properly controlled experiments that are relevant to beekeepers is almost impossible. 2. Easier for researchers to look for correlations between presence of causative factors and colony mortality. Correlation is NOT causation. Recent report of Nosema ceranae and virus was interesting, but because it did not consider pesticides if is being attacked. 3. An answer found in one location may not be the answer in another.

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16 Statistics! How do you tell if two averages differ? Low variation good estimate of the mean; Small study with only a few bee hives can yield significant results. High variation- difficult to estimate the mean; Need much larger sample of bee hives to be certain of difference

17 Example of use of statistics Mortality of two groups of honey bee colonies: 40% of mite-infested hives die vs. 20% of control colonies (no mites) die: Is mortality in these two groups different or simply due to chance? Sample size is important: - If only 5 hives in each group, unlikely they differ: 2/5 vs 1/5 difference of only one colony - If 50 hives in each group were studied: 20/50 vs 10/50 we would agree these differ.