Comparison of nonchemical, organic and synthetic Varroa destructor control strategies in honey bee colonies: effects on parasite load, colony strength and health

BACKGROUND: Varroa destructor remains the most significant biotic threat to honey bee colonies, and increasing resistance to synthetic acaricides necessitates alternative control strategies. This study compared four season-long Varroa management strategies that differed in spring drone-brood management and late-summer treatment strategy: (i) synthetic treatment without drone-brood removal; (ii) the organic Baden-Württemberg (BW) concept; (iii) an integrated oxalic acid 'split and treat' strategy; and (iv) brood availability manipulation (BAM), a biotechnical strategy combining systematic drone-brood removal and queen confinement. RESULTS: Intensive drone-brood removal effectively suppressed seasonal mite population growth, whereas more limited removal provided only moderate control. Colonies in the synthetic treatment strategy, which did not include drone-brood removal, exceeded treatment thresholds by mid-summer. Late-summer treatment efficacy differed among strategies, with BAM and the BW concept achieving the most consistent mite reduction, whereas the integrated strategy showed lower and more variable efficacy. Residual infestation levels reflected these differences. CONCLUSION: Colony performance, including strength, worker emergence weight, fat body reserves and virus prevalence, did not differ among treatments. No statistically detectable differences in honey yield were observed, although this exploratory analysis was limited by the number of colonies within individual treatment groups. Winter bee longevity showed minor variation, with slightly extended survival in BAM colonies. These findings demonstrate that seasonally integrated biotechnical management can effectively control V. destructor without compromising colony performance, providing a sustainable alternative to synthetic acaricides under temperate Central European conditions.