Deformed wing virus prevalence and load in honeybees in South Africa
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BRIEF REPORT
Deformed wing virus prevalence and load in honeybees in South Africa Flaviane S. de Souza1,2 · Michael H. Allsopp3 · Stephen J. Martin1 Received: 16 July 2020 / Accepted: 16 September 2020 © The Author(s) 2020
Abstract Deformed wing virus (DWV) is an emerging honeybee pathogen that has appeared across the globe in the past 40 years. When transmitted by the parasitic varroa mite, it has been associated with the collapse of millions of colonies throughout the Northern Hemisphere. However, despite the presence of the mite in the Southern Hemisphere, infested colonies survive. This study investigated the prevalence of DWV genotypes A, B and C along with their viral loads in South Africa and compared the findings with recent data from Brazil, the UK and the USA. We found that DWV-B was the most prevalent genotype throughout South Africa, although the total DWV viral load was significantly lower (2.8E+07) than found in the Northern Hemisphere (2.8E+07 vs. 2.7E+10, p > 0.00001) and not significantly different to that found in Brazil (5E+06, p = 0.13). The differences in viral load can be explained by the mite resistance in Brazil and South Africa, since mite-infested cells containing high viral loads are removed by the bees, thus lowering the colony’s viral burden. This behaviour is much less developed in the vast majority of honeybees in the Northern Hemisphere. Deformed wing virus (DWV) is a newly emerging pathogen that within 40 years from its discovery has become the most widespread insect virus. DWV has been detected in over 50% of all honeybee colonies in 32 countries at high viral loads and in 65 arthropod species spanning eight orders [1]. Prior to the global spread of a highly pathogenic parasitic mite, Varroa destructor, there was a least one known honey bee colony collapse linked to high DWV loads (>107 viral particles/bee) (unpublished data, SJM). Recently, more-sensitive testing has shown that the DWV prevalence in varroafree honeybee populations is highly variable, being absent in Australia [2], low in Hawaii [3], and high in Newfoundland [4], but viral loads are typically very low. The recent success of DWV is due to its close association with an ectoparasitic mite (Varroa destructor) that lives on honeybees and Handling Editor: T. K. Frey. * Stephen J. Martin [email protected] 1
School of Environment and Life Sciences, The University of Salford, Manchester M5 4WT, UK
2
Universidade Federal do Recôncavo da Bahia, Rua Rui Barbosa 710, Cruz das Almas, Bahia 44380‑000, Brazil
3
ARC-Plant Protection Research Institute, P/Bag X5017, Stellenbosch 7599, South Africa
during the past 70 years has spread globally [5]. Molecular evolutionary clocks [6] have demonstrated the possible appearance of widespread DWV-related pathologies with the arrival of Varroa mites. The mite has introduced a new viral transmission route when feeding on the honeybee, causing elevated DWV levels and selecting for highly virulent DWV variants [4] or the appearance of pathogenic strains that outcompete
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