Risk factors for the presence of Deformed wing virus and Acute bee paralysis virus under temperate and subtropical climate in Argentinian bee colonies.

Beekeepers all across the world are suffering important losses of their colonies, and the parasitic mites Varroa destructor and Nosema sp, as well as several bee viruses, are being pointed out as the possible causes of these losses, generally associated with environmental and management factors. The objective of the present study was to evaluate the presence of seven virus species (Deformed wing virus -DWV-, Acute bee paralysis virus -ABPV-, Chronic bee paralysis virus -CBPV-, Black queen cell virus -BQCV-, Kashmir bee virus -KBV-, Israeli acute bee paralysis virus -IAPV-, and Sacbrood bee virus -SBV), as well as the prevalence of Nosema sp. and Varroa destructor, and their possible associated factors, under temperate and subtropical climate conditions in Argentinean colonies. A total of 385 colonies distributed in five Argentinean eco-regions were examined after honey harvest. The final multivariable model revealed only one variable associated with the presence of DWV and two with the presence of ABPV. The apiary random effect was significant in both cases (P=0.018; P=0.006, respectively). Colonies with a Varroa infestation rate >3% showed higher presence of DWV than colonies with <3% of Varroa infestation level (OR=1.91; 95% CI: 1.02-3.57; P<0.044). The same pattern was observed for the presence of ABPV (OR=2.23; 95% CI: 1.04-4.77; P<0.039). Also, colonies where replacement of old combs was not a common practice had higher presence of ABPV (OR=6.02; 95% CI: 1.16-31.25; P<0.033). Regardless of the location of the colonies, virus presence was strongly associated with V. destructor level. Therefore, all the factors that directly or indirectly influence the levels of mites will be also influencing the presence of the viruses.

Key management practices to prevent high infestation levels of Varroa destructor in honey bee colonies at the beginning of the honey yield season.

Varroa destructor is considered one of the main threats to worldwide apiculture causing a variety of physiological effects at individual and colony level. Also, Varroa mites are often associated with several honey bee viruses presence. Relatively low levels of Varroa during the spring, at the beginning of the honey yield season, can have a significant economic impact on honey production and colony health. Winter treatments against Varroa and certain management practices may delay mite population growth during following spring and summer improving colonies performance during the honey yield season. The aim of this study was to identify risk factors associated with the presence of Varroa destructor in late spring in apiaries from temperate climate. A longitudinal study was carried out in 48 apiaries, randomly selected to evaluate V. destructor infestation level throughout the year. The percentage of infestation with V. destructor was assessed four times during one year and the beekeepers answered a survey concerning all management practices applied in the colonies. We used a generalized linear mixed model to determine association between risk of achieving 2% infestation on adult bees at the beginning of the honey yield season and all potential explanatory variables. The complete dataset was scanned to identify colonies clusters with a higher probability of achieving damage thresholds throughout the year. Colonies that achieved ≥2% of infestation with V. destructor during spring were owned by less experienced beekeepers. Moreover, as Varroa populations increase exponentially during spring and summer, if the spring sampling time is later this growth remains unobserved. Monitoring and winter treatment can be critical for controlling mite population during the honey production cycle. Spatial distribution of colonies with a higher risk of achieving high Varroa levels seems to be better explained by management practices than a geographical condition.