In this research, the absorption and release rate of the essential oil, Amomum krervanh, by seven different materials were evaluated. Cardboard showed the highest EO absorption capacity (0.93 ± 0.0052 μL of oil/mg of dry cardboard) followed by balsa wood and drawing board with the EO absorption of 0.77 ± 0.043 and 0.62 ± 0.010 μL of oil/mg of dry material, respectively. The results also demonstrated that cardboard had the highest EO retention (52.84 ± 0.687% after 20 min of analysis). Additionally, the essential oil was released from the drawing board and cardboard at the same rate during the observation period. Surface modification of drawing board and cardboard was performed using atmospheric-pressure plasma for enhancing the material properties for Tropilaelaps control. The absorption capacity of cardboard was decreased after plasma treatment at an argon flow rate of 0.25 and 0.5 Lpm for 60 s/cm2. However, the atmospheric-pressure plasma did not change the EO release property of these materials. Scanning electron microscopy analyses indicated a fractured and scaly surface after plasma treatment of gas flow rate at 0.5 Lpm and 1.0 Lpm for 30 s/cm2. The surface chemical composition of materials was not altered following plasma treatment. Although the number of mite-infested brood cells did not differ significantly between treatment groups at the end of the field experiment, Tropilaelaps spp. populations in the plasma-treated cardboard impregnated with EO 5% (v/v) treatment were lower on days 7–14 of the experiment. Thus, parameters related to the atmospheric-pressure plasma should be further optimized to improve the material surfaces for use with essential oils to control honeybee mites.
Tropilaelaps spp. mites are considered a major parasite of honeybees. In this study, essential oils (EOs) of 11 plant species were evaluated for acaricidal activity under laboratory and field conditions. Five adult mites per petri dish and ten adult worker bees per plastic cup cage were exposed to different concentrations of each essential oil (0.1, 0.5, 1.0, 5.0, and 10.0% (v/v)). The essential oil of Piper betle (betel) showed the highest acaricidal activity in laboratory testing. Additionally, most EOs showed low toxicity to adult honeybees in a lab assay. Piper betle , Amomum krervanh , and Zanthoxylum limonella were then tested in whole colonies using cardboard strips soaked in 10 mL of each essential oil at various concentrations, every week for 4 weeks. Amomum krervanh at 10% (v/v) and P. betel at 5.0% (v/v) decreased mite populations after 30 days. We further tested grease and a sponge as application methods to deliver A. krervanh , with no significant impact on mites. Although several essential oils demonstrated acaricidal activity against Tropilaelaps under laboratory conditions, the EOs tested did not significantly reduce mites under colony conditions. Therefore, the concentration and colony delivery methods of these promising EOs warrant further investigation.Tropilaelaps / acaricidal activity / LC 50 / Apis mellifera / Piper betle / Amomum krervanh
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