Promising antimicrobial activity against the honey bee parasite Nosema ceranae by methanolic extracts from Chilean native plants and propolis

Abstract

The gut parasite Nosema ceranae is one of the most prevalent honey bee microsporidia worldwide and its chemical management in American countries is mainly based on the antibiotic fumagillin. However, it has recently been reported that this drug has negative side effects in honey bees; therefore, non-harmful alternative treatments must be found. The effects of methanolic extracts (2, 4, 8 and 16%) from Chilean native plant leaves (Aristotelia chilensis, Ugni molinae, and Gevuina avellana) and propolis (Biobío (BB) and Los Ríos (LR) regions) on N. ceranae load, diet consumption and the survival of N. ceranae-infected honey bees were evaluated through oral intake. When bees were N. ceranae-infected and treated with extracts of A. chilensis (8%), U. molinae (2 and 8%) and propolis BB (8%) simultaneously, the N. ceranae load decreased significantly and the survival of infected bees also improved. On the other hand, when bees were first extracts-treated and then N. ceranae-infected, their diet consumption increased and all extracts significantly decreased the N. ceranae load in infected bees. However, only extracts from U. molinae (2 and 8%) and propolis LR (8%) maintained a higher survival rate in infected bees. Natural compounds were also identified; U. molinae and A. chilensis leaves had high concentrations of rutin and myricetin, whereas galangin and pinocembrin were found mostly in southern Chilean propolis (LR). This study constitutes the first report of the antiparasitic activity of propolis against N. ceranae in Apis mellifera and the antimicrobial activity of Chilean plant extracts against this honey bee parasite.

Actividad antimicrobiana prometedora de extractos metanólicos de plantas nativas y propóleos chilenos contra el parásito de las abejas Nosema ceranae (Microsporidia)

El parásito intestinal Nosema ceranae es uno de los patógenos de la abeja melífera más importante y prevalentes en el mundo. En América, su control se basa principalmente en el uso del antibiótico fumagilina. Sin embargo, estudios recientes han reportado que este medicamento tiene efectos secundarios sobre las abejas y por lo tanto, es necesario encontrar tratamientos alternativos. Se evaluaron diferentes concentraciones (2, 4, 8 y 16%) de extractos metanólicos de hojas de plantas nativas (Ugni molinae, Aristotelia chilensis y Gevuina avellana) y propóleos chilenos (regiones de Biobío (BB) y Los Ríos (LR)) sobre el consumo de la dieta, la carga de N. ceranae y la sobrevivencia de las abejas. Cuando las abejas fueron tratadas con extractos e infectadas con N. ceranae al mismo tiempo, A. chilensis (8%), U. molinae (2 y 8%) y propóleos BB (8%) disminuyeron significativamente la carga de N. ceranae y mejoraron la sobrevivencia de las abejas. Por otra parte, cuando las abejas fueron primero tratadas con extractos y luego infectadas con N. ceranae, éstas mostraron un mayor consumo de la dieta y también, todos los extractos disminuyeron significativamente la carga de N. ceranae, pero solo los extractos de U. molinae (2 y 8%) y propóleo LR (8%) mantuvieron una alta sobrevivencia de abejas infectadas con N. ceranae. Se detectaron altas concentraciones de rutina y miricetina en los extractos metanólicos de U. molinae y A. chilensis, mientras que la galangina y pinocembrina se encontraron principalmente en propóleos del sur de Chile (LR). Este estudio constituye el primer reporte de la actividad antiparasitaria de extractos metanólicos de propóleos y de plantas chilenas contra N. ceranae en A. mellifera.

Keywords:

• Aristotelia chilensis
• Ugni molinae
• Gevuina avellana
• propolis
• Nosema ceranae
• honey bee

Acknowledgments

We are grateful to Pamela Jara for her technical support in the HPLC-DAD analysis. We would also like to thank Tomás Venegas and Gustavo Riveros for their valuable help in the inoculation assays in laboratory conditions and for their laboratory support.