Lippia alba essential oil as potential control agents of chalkbrood

ALBO GN; ALTAMIRANO R.; REYNALDI FJ.; CÓRDOBA SB.

Estambul

Congreso; 45th Apimondia International Apicultural Congress; 2017

Apimondia

Chalkbrood is a fungal infection of Apis mellifera caused by Ascosphaera apis. A total of 48 isolates of A. apis obtained from honeybee larvae from Argentina and Chile were studied. We used the agar diffusion method to determine the minimal inhibitory concentration (MIC) of essential oils (range 50-1600 μg/mL) obtained from L. alba (Verbenaceae) carvone and linalol chemotypes. Controls: 50% sucrose-water, diluent (2.5% propylene glycol) and ketoconazole (effectiveness) (1 mg/mL). The inoculum was made from cultures of A. apis left 7-10 days, at 35 °C in agar MY20. Holes of 7 mm in diameter were made in the agar plates with A. apis cultures. Then, the inocula were placed in the agar plates containing MY20, essential oils and the diluent. The plates were incubated at 35 °C in the dark, and read every 24 h up to 144 h. Visual reading was measured with a ruler. The results were analyzed using ANOVA and Tuckey (p ≤ 0.05). The identification of the essential oils was performed by GC-MS. The Median Lethal Dose (LD50) was determined in adult bees. Concentrations were expressed in micrograms of active principle per bee (μg p.a/bee). L. alba carvone and linalol were evaluated at concentrations 2-64 (μg p.a/bee), dimethoate (toxic control) at 0.02-0.64 (μg p.a/bee) and diluent control (2.5% alcohol). The adult bee mortality was determined at 24, 48, 72 h. The LD50 was performed with PROBIT. The components identified were L. alba carvone (35.3% limonene and 29.9% carvone) and linalol (41.4% linalol and 19.4%, 1.8 cineol). The CIM50 of L. alba carvone and linalol were 800 and 1600 μg/mL, respectively. Significant differences were observed among the isolates, essential oils and concentrations (p ≤ 0.0000) at 72 and 144 h. The carvone chemotype was more effective than linalool. The LD50 of dimethoate was 0.28-0.13 μg p.a/bee, considered normal for "highly toxic" products. The essential oil of L. alba carvone and linalool resulted "virtually non-toxic" at 24, 48 and 72 h. This study might be a starting point for future researches of L. alba essential oils, as they offer a good alternative in the control of chalkbrood.