Evaluación de la actividad inhibitoria, in vivo e in vitro, del aceite esencial de Cymbopogon citratus y cinco diluyentes sobre cultivos de Ascosphaera apis

The minimal inhibitory concentration (MIC) of the essential oil of Cymbopogon citratus and five diluents against Ascosphaera apis crops was evaluated. Toxicity in adult bees was determined. Also, the selectivity ratio of the essential oil-diluents’ formulation was calculated. The MIC was determined by agar diffusion in MY20 medium against 28 isolates of A. apis from Argentina and Chile. Diluents Tween 80, dimethyl sulfoxide (DMSO), propylene glycol (PG), alcohol 70° and water at the concentrations 150, 250, 500 and 750 mg/l, formulated in the diluent 2.5 % v/v were used. The acute oral toxicity on adult honey bee was tested for C. citratus in combination with PG and alcohol 70°, using dimethoate as toxic control. Alcohol 70° was the best diluent for C. citratus since it exhibited a MIC90 of 250 mg/l, was “virtually non-toxic” for adult bees and showed a selectivity ratio of 6 μL /bee at 72 hours, being the essential oil-diluent formulation least toxic to control A. apis in honey bee colonies.