Effect of systemic administration of essential oils and main components on honeybee survival

Controlling bee diseases with non contaminant products is a challenge in apicultural research. Essential oils and their main components have been widely studied as alternative treatments for honeybee pathologies [1, 2, 3]. However, there is little information about prolonged systemic administration. The aim of this study was to evaluate, in laboratory assays, the effect of long term consumption of essential oils and main components. Oils were obtained by hydrodistillation from Laurus nobilis, Cinnamomun zeylanicum, Origanum vulgare, Rosmarinus officinalis and Eucalyptus spp. and were analyzed by gas chromatography. The main components administered were 1,8-cineol, β-myrcene, cinnamic aldehyde, carvacrol and α-phellandrene. Substances were administered ad libitum to newly emerged bees at concentrations of 0; 333; 3,333 and 6,666 ppm, on sucrose syrup, throughout 11-18 days. Mortality and substances consumption were measured daily. Survival analysis was performed using Gehan-Breslow test and pairwise multiple comparisons between survival curves (a= 0, 05). Substances consumption was analyzed using one way ANOVA. Bees that received cinnamon oil showed a lower survival than control at concentrations higher than 333 ppm (pvalues<0.001 ). Consumption of cinnamic aldehyde, the main component of this oil (79.3%), also caused lower survival at the same concentrations (p-values<0.001). Eucalyptus oil caused a lower survival rate when it was administered at 6,666 ppm, although 1,8 cineol, its main component (63.5%), was not toxic for bees at any concentration. Carvacrol, a main component of many oregano essential oils, showed toxic effects at 3,333 and 6,666 ppm. Essential oils did not cause differences in consumption rate (p= 0.275) while main components solutions, except for carvacrol, were less consumed than control at the three concentrations. Treatments did not cause dysentery to bees. Our results contribute to understanding the effect of repeated systemic doses of these substances, which is important to design long term pharmacological studies and treatments development

Antimicrobial activity of essential oils against Paenibacillus larvae

American foulbrood is a serious bacterial disease that affects Apis mellifera colonies; the causative agent is Paenibacillus larvae [1 ]. The aim of the study was to evaluate in vitro the antimicrobial activity of 32 essential oils against P. larvae. Oils from 21 botanical species were analyzed by gas chromatography (CG and CG/EM). All essential oils were classified according to the composition of their main components in two groups: benzene ring compounds (BRC) and terpene compounds (TC). Minimal inhibitory concentration (MIC) in MYT broth [2] was assessed by the microdilution method. Final serial dilution concentrations of the essential oils ranged between 2,000-12.5 mgll. The bacterial isolates were collected from different Argentina's region. The chromatographic analysis showed that a 67% of the essential oils contained predominately terpene compounds. while the remaining 33% included mainly compounds with benzene rings. From the TC group, Cymbopogon citratus essential oil showed the better antimicrobial activity against P. larvae with MIC values between 150 and 250 mgl l. The essential oi ls from Aloysia polystachya and Mentha spp. had the lowest inhibitory activity. Among the oils from the BRC group, one of the lowest MIC values was found with cinnamon essential oil (Cinnamomun zeylanicum) being between 25 and 50 mg/L; Origanum vulgare showed the highest MIC values (350-400 mg/L). Essential oils, especially those with BRC in their composition, presented inhibitory capacity against P. larvae strains

Nota corta. Evaluación de aceites esenciales de dos plantas silvestres y sus emulsificantes utilizados en tests de inhibición de Paenibacillus larvae subsp. Larvae

In honey bees (Apis mellifera L.), American foulbrood (AFB) is caused by the infection of the larvae and pupae with the bacterium Paenibacillus larvae subsp. larvae. The antibacterial effects of the essential oils of wild camomile (Tagetes minuta L.) and Andean thyme (Acantholippia seriphioides A. Gray) against different strains of P. larvae subsp. larvae were evaluated in vitro. The possible inhibitory effects of two emulsifiers of these oils (propylene glycol and soybean lecithin) were also assessed. Significant differences in antibacterial action were seen between the oils and emulsifiers (PLa patología conocida como loque americana, que afecta a los estadios de larva y pupa de abejas (Apis mellifera L.), es causada por la bacteria Paenibacillus larvae subsp. larvae. Se evaluó el efecto antibacteriano in vitro de los aceites esenciales de manzanilla silvestre (Tagetes minuta L.) y tomillo andino (Acantholippia seriphioides A. Gray) frente a diferentes cepas de P. larvae subsp. larvae, así como también el posible efecto inhibitorio adicional del propilenglicol y la lecitina de soja, utilizados como emulsionantes de los aceites esenciales. Los resultados de la evaluación in vitro indican diferencias significativas entre los dos aceites esenciales emulsionados (

Antimicrobial and miticide activities of Eucalyptus globulus essential oils obtained from different Argentine regions

The biological activity of Eucalyptus globulus essential oils derived from plant material obtained from different geographic areas was analyzed in in vitro experiments on Paenibacillus larvae, Varroa destructor, and Apis mellifera. The physicochemical properties, composition, antimicrobial, and bioactivity of these essential oils were studied. The bioactivity against P. larvae was analyzed by means of two in vitro techniques (tube dilution and bioautography). Mite and bee lethality were estimated using a complete exposure method test with oils at different concentrations. Essential oils differed in their composition, albeit their similar physicochemical properties. The minimal inhibitory concentrations range for E. globulus essential oil lay between 600-700 ìg mL�1 for Mar del Plata and 900-1,200 ìg mL�1 for Valle de Conlara essential oils against all P. larvae strains. The bioautography method determined that limonene accounted for the greatest antimicrobial activity with respect to the other compounds. The complete exposure method at 24, 48, and 72 h yielded lower LC50 values for mites exposed to E. globulus essential oils from Conlara. LC50 values for acari after 72 h of treatment with E. globulus from Mar del Plata and Conlara were 47.1 and 11.7 ìL capsule�1, respectively; whilst those for bees was > 20 ìL capsule�1 for both oils. The E. globulus essential oils tested in this study featured high efficiency against V. destructor, yet their antimicrobial activity against P. larvae proved to be lower, and innocuous to bees. The present experience promotes the use of active compounds for American fouldbrood and Varroosis management.Se analizo la actividad biologica de los aceites esenciales de Eucalyptus globulus, derivados de material vegetal obtenido de diferentes regiones geograficas, en experimentos in vitro sobre Paenibacillus larvae, Varroa destructor y Apis mellifera. Se estudiaron las propiedades fisicoquimicas, composicion, actividad antimicrobiana y bioactividad de estos aceites esenciales y se analizo la bioactividad frente a Paenibacillus larvae por dos tecnicas in vitro (dilucion seriada y bioautografia). Se estimo la letalidad en acaros y abejas con los aceites esenciales a diferentes concentraciones, usando un metodo de exposicion completa. Los aceites difirieron en su composicion, aunque presentaron propiedades fisicoquimicas similares. La concentracion inhibitoria minima frente a los aislamientos de P. larvae para los aceites de E. globulus fue 600-700 �Êg mL.1 para Mar del Plata y 900-1.200 �Êg mL.1 para Valle de Conlara. La tecnica de bioautografia determino que el limoneno fue el compuesto con la mayor actividad antimicrobiana. El metodo de exposicion completa a las 24, 48, y 72 h mostro valores de LC50 menores para acaros expuestos al aceite esencial de E. globulus de Conlara. Los valores de LC50 para acaros a las 72 h de tratamiento fueron 47,1 y11,7 �ÊL capsula.1 para E. globulus de Mar del Plata y Conlara, respectivamente; mientras que para las abejas fue > 20 �ÊL capsula.1 para ambos aceites. Los aceites esenciales de E. globulus estudiados mostraron mayor efectividad frente a V. destructor en relación a P. larvae, probando ser inocuos para las abejas. El presente trabajo promueve el uso de los componentes activos de estos aceites para un manejo de las enfermedades Loque americana y Varroosis