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New Zealand: a unique location for studying the interactions between bees, Varroa and viruses

When researchers wanted to examine the influence of the parasitic mite Varroa on viruses in honeybee colonies, they found a unique studying ground in New Zealand. Researchers from INRA and the University of Otago teamed up to investigate a large zone that had both Varroa-infested and Varroa-free areas. They studied the viral landscape of honeybee colonies following the parasite’s recent invasion (since 2001) of the area and showed that the arrival of Varroa coincided with a drastic modification of the viral landscape within colonies. The mite increased interactions between different viruses in the colonies, bringing about synergistic effects that threaten their survival.

Varroa on thorax of honeybee. © INRA, MORISON Nicolas
By INRA News Office
Updated on 01/06/2015
Published on 10/24/2014

Over the past fifty years, the parasitic mite Varroa destructor has been responsible for massive honeybee hive deaths. V. destructor is now considered to be one of the major determining factors in honeybee survival due to its associations with various bee parasites. Without effective Varroa infestation control, viral epidemics take root and cause colonies to swiftly collapse.

Varroa favour viral infections

- Map illustrating the spread of Varroa across New Zealand.The black dots represent the 22 hives sampled for the study.. © PLOS Pathogens, Fanny Mondet et al.
- Map illustrating the spread of Varroa across New Zealand.The black dots represent the 22 hives sampled for the study. © PLOS Pathogens, Fanny Mondet et al.

Varroa, seen for the first time in France in 1982, has since infested colonies across the world, with the exception of Australia. New Zealand, where Varroa arrived in 2001, presented a unique opportunity to study interactions between bees, Varroa and related viruses because the mite had not yet invaded the entire country when the study began. The country had an active infestation expansion front moving southward into areas where the mite had not yet arrived. INRA researchers took samples from 22 hives from professional beekeepers in New Zealand to monitor the initial stages of Varroa infestation and its effect on viruses within bee colonies. Five viruses1 were detected in the bee and Varroa samples. Each of them reacted differently to the parasite’s arrival. Researchers observed that with Varroa’s arrival, there was an increase in multiple viral infections, rising from an average of 1.6 to 3.1 viruses per colony.

 

Prevalence of the Deformed Wing Virus

- Pathological manifestation of DWF in young bees infested with Varroa mites. © INRA, Fanny Mondet
- Pathological manifestation of DWF in young bees infested with Varroa mites © INRA, Fanny Mondet

Deformed Wing Virus (DWV) seems to be helped the most by the mite’s spread throughout New Zealand. This virus, viewed as a direct cause of bee deaths in colonies infested by Varroa, was not found in Varroa-free areas. The prevalence of DWV gradually increases along with the number of years infestation continues, even when Varroa rates decline. The spread of another extremely virulent virus transmitted by Varroa, the Kashmir Bee Virus (KBV), appears to be closely linked to Varroa infestation. Contrary to DWV, KBV rates increase very quickly during the first two years of infestation before declining and finally disappearing from the colonies, leaving DWV as the dominant virus in regions infected by Varroa for more than ten years.

These results reinforce the idea that the association between Varroa and several bee viruses is a key factor in explaining colony deaths tied to Varroa infestations.For example, KBV may play a role in high colony losses observed in the first few years of Varroa infestation, while DWV is most certainly implicated in bee deaths in regions with a long-standing Varroa infestation. The underlying mechanisms of these complex interactions between bees, Varroa and viruses need to be better understood to improve strategies to fight Varroa and ensure colony health.

 

(1) Deformed Wing Virus (DWV), Kashmir Bee Virus (KBV), Black Queen Cell Virus (BQCV), Chronic Bee Paralysis Virus (CBPV) and Sacbrood Virus (SBV).

Contact(s)
Scientific contact(s):

Press Relations:
INRA News Office
Associated Division(s):
Plant Health and Environment
Associated Centre(s):
Provence-Alpes-Côte d'Azur

Reference

Fanny Mondet, Joachim R. de Miranda, Andre Kretzschmar, Yves Le Conte, Alison R. Mercer (2014). Quantitative Virus Dynamics in Honeybee (Apis mellifera L.) Colonies along a New Expansion Front of the Parasite Varroa destructor. PLOS Pathogens. 10(8): e1004323. DOI:10.1371/journal.ppat.1004323