We have some fairly recent pathogen test results here in Newfoundland and Labrador that I would like to discuss with participants in this LIST-SERV. You will remember that we remain Varroa-naïve, at least for the time-being.
The first survey research to establish some kind of comprehensive baseline of our honey bee pathogens, pests and diseases was conducted in 2010 by a team of researchers, presumably lead by the senior reporting author, Dave Shutler, Acadia University, Nova Scotia (Shutler, et al., 2014). Testing was conducted by Abby Levitt at the Department of Entomology, Pennsylvania State University. In this research, 55 (47.8%) of 115 colonies across five apiaries on the Island of Newfoundland were inspected and sampled in June 2010. Visual assessments were conducted to assess colony strength and determine the presence/absence of K-wing, Chalkbrood, AFB, EFB, SHB, and Tropilaelaps spp. ectoparasitic mites (ibid.:2). Qualitative assessments were conducted of 23 randomly chosen colony samples at Penn State using molecular screening methods (e.g, RT-PCR) for several viruses including BQCV, DWV, IAPV, KBV, and SBV. The Entomology Department at Penn also conducted quantitative and qualitative assessments for Nosema apis, Nosema ceranae, Acarapis woodi, and Varroa destructor mites. Of the 23 colonies sampled for viruses, one sample was discarded due to degraded RNA, and of the remaining 22 colonies none tested positive for ICPV, KBV, or SBV. DWV WAS DETECTED IN ALL 22 COLONY SAMPLES (my emphasis).
During the 2016 season, the Government of Newfoundland and Labrador’s provincial apiarist inspected and sampled five apiaries for various pathogens and pests as part of the Canadian National Honey Bee Health Survey. Survey/test results and methods from the 2016 sampling are reported in National Bee Diagnostic Centre’s report. See https://www.gprc.ab.ca/research/initiatives/nbdc/projects/current/nat_survey.html
In addition to testing for several pathogens not included in previous surveys, the 2016 survey/tests detected EFB and SBV and confirmed the presence of Nosema ceranae in the domestic NL honey bee stock. What I want to draw your attention to is the finding that all of the 2016 samples tested negative for DWV (see Figure 17 in the survey report - https://www.gprc.ab.ca/doc.php?d=2016NHBHS ). A 2017 sample from my own apiary, tested by the Animal Health Laboratory at the University of Guelph (qPCR), also was negative for DWV.
I find these test results for DWV somewhat perplexing given that DWV is apparently an endemic honey bee pathogen worldwide that co-evolved with the Apis species (Wilfert, et al., 2016). How it is that the virus tested negative in all 2016 domestic samples as well as my 2017 sample when it was highly prevalent in 2010 sampling? How could DWV disappear from the NL domestic stock between 2010 and 2016? Or, was testing of the 2010 samples blemished by methodological problems such as false positives that invalidate the results? Or perhaps 2016 sampling was blemished by methodological problems?
At the same time I note Nancy Ostiguy’s (2010) seven state long-term study of 30 stationary colonies per location aimed at generating epidemiological data to characterize colony health across the U.S. Inter alia, her results showed seasonal changes in virus prevalence. “Deformed wing virus prevalence increased from 55% to 96% of bees tested from Maine. The bees in Maine began with the lowest prevalence of DWV (55%), but by August the prevalence of DWV was the highest (96%).” The regional prevalence of DWV (% of positive samples) was 83% for Florida, 55% for Maine, 56% for Minnesota, 74% for Pennsylvania, 96% for Texas, and 61% for Washington. Clearly, not all bees carry DWV, at least in amounts detectable using PCR methodologies.
Anyone care to offer an explanation or interpretation of our test results for DWV?
References
Ostiquy, N. 2010. A Peek at the Distribution of Viruses in Stationary Honey Bee Colonies in the U.S.” American Bee Journal. Proceedings of the American Bee Research Conference, January 14-15, 2010. Pp.504-505.
Shutler, Dave, Krista Head, Karen L. Burgher-MacLellan, Megan J. Colwell, Abby L. Levitt, Nancy Ostiguy, Geoffrey R. Williams. 2014. “Honey Bee Apis mellifera Parasites in the Absence of Nosema ceranae Fungi and Varroa destructor Mites.” PLOS One. 9(6): E98599. Doi:10.1371/journal.pone.0098599.
Wilfert, L., G. Long, H.C. Leggett, P. Schmid-Hempel, R. Butlin, S.J.M. Martin and M. Boots. 2016. “Deformed Wing Virus is a Recent Global Epidemic in Honeybees Driven by Varroa Mites.” Science. 351(6273):594-597.
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