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BACKGROUND: The parasitic mite, Varroa destructor has posed a threat to the health and survival of European honey bees, Apis mellifera worldwide. There is a prevailing belief that small comb cells could provide a management tool against Varroa mites. However, the hypothesis that smaller cells can impede Varroa reproduction has not been fully tested. Here, we tested this hypothesis under laboratory conditions by using two distinct Varroa in vitro rearing systems: one involved gelatin capsules of different sizes, specifically size 00 (0.95 mL) versus size 1 (0.48 mL), and the second consisted of brood comb cells drawn on 3D printed foundations with varying cell sizes, ranging from 5.0 mm to 7.0 mm at 0.5 mm intervals. RESULTS: The results showed that mother mites in size 00 cells had significantly lower fecundity and fertility compared to those in size 1 cells. Interestingly, the reproductive suppression in larger cells could be reversed by adding an extra worker larva. Similarly, gonopore size of mother mites was smaller in size 00 cells, but restored with another host larva. Furthermore, both the fecundity and fertility of mother mites decreased linearly with the size of brood comb cells. CONCLUSIONS: Our results suggest that the reproduction of V. destructor is hindered by larger cells, possibly because larger brood cells disperse or weaken host volatile chemical cues that are crucial for Varroa reproduction. The insights derived from this study are expected to hold significant implications for the implementation of Varroa management programs. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Honey bees are crucial for ecosystem pollination and honey production, yet the Varroa destructor mite hinders their productivity and health. Efforts to manage Varroa mites with synthetic pesticides have had limited success, highlighting the need for naturally derived acaricides as a primary option. However, the acaricidal efficacy of essential oils from Salvia officinalis L. (sage), Cannabis sativa (hemp), and Laurus nobilis (laurel) remains to be fully understood. This study aims to investigate the acaricidal efficacy of these three essential oils at varying concentrations and their impact on honey production, focusing on the efficient reduction in Varroa mites. The sugar roll method was employed to assess Varroa mite infestation levels, while GC-MS analysis was utilized to verify the composition of the essential oils. Honey production measurements were also performed. The efficacy rates (%) at concentrations of 15%, 10%, and 5% for hemp oil were 95.4% ± 0.30%, 85.71% ± 0.85%, and 64.48% ± 0.26%, respectively; for sage oil, they were 81.08% ± 0.57%, 69.42% ± 1.72%, and 50.35% ± 0.70%; and for laurel oil, they were 68.96% ± 0.34%, 54.66% ± 0.37%, and 33.58% ± 0.30%, respectively. Key compounds identified include trans-caryophyllene, α-pinene, and viridiflorol in hemp oil; myrcene, limonene, and β-caryophyllene in sage oil; and phytol, β-myrcene, and n-heneicosane in laurel oil. The overall findings indicate that hemp oil is highly effective in controlling Varroa mites. However, further research is needed to evaluate its potential side effects on bees to ensure its sustainability and safety. [ABSTRACT FROM AUTHOR]