Nosema ceranae causes a widespread disease that reduces honey bee health but is only thought to infect adult honey bees, not larvae, a critical life stage. We reared honey bee (Apis mellifera) larvae in vitro and provide the first demonstration that N. ceranae can infect larvae and decrease subsequent adult longevity. We exposed three-day-old larvae to a single dose of 40,000 (40K), 10,000 (10K), zero (control), or 40K autoclaved (control) N. ceranae spores in larval food. Spores developed intracellularly in midgut cells at the pre-pupal stage (8 days after egg hatching) of 41% of bees exposed as larvae. We counted the number of N. ceranae spores in dissected bee midguts of pre-pupae and, in a separate group, upon adult death. Pre-pupae exposed to the 10K or 40K spore treatments as larvae had significantly elevated spore counts as compared to controls. Adults exposed as larvae had significantly elevated spore counts as compared to controls. Larval spore exposure decreased longevity: a 40K treatment decreased the age by which 75% of adult bees died by 28%. Unexpectedly, the low dose (10K) led to significantly greater infection (1.3 fold more spores and 1.5 fold more infected bees) than the high dose (40K) upon adult death. Differential immune activation may be involved if the higher dose triggered a stronger larval immune response that resulted in fewer adult spores but imposed a cost, reducing lifespan. The impact of N. ceranae on honey bee larval development and the larvae of naturally infected colonies therefore deserve further study.

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Since Nosema ceranae causes mortality in honey bee populations in both managed apiaries and in the wild, many chemical compounds have been screened and tested for their abilities to suppress populations of N. ceranae. However, the use of synthetic substances has resulted in residues in colonies and honey bee products. The development of new methods for the control of nosema disease is therefore much needed by beekeepers and bee scientists. We evaluated the effects of propolis from the stingless bee Trigona apicalis on N. ceranae-infected Asian honey bees, Apis cerana. One-day-old N. ceranae free worker bees were individually inoculated with 2 μl of 50% sucrose solution containing 80,000 N. ceranae spores per bee and then fed with 50 and 70% (v/v) propolis extract in water. All propolis-treated bees had significantly higher survival rates than untreated bees (F 5 = 92.6, p < 0.0001). Bees treated with the highest propolis concentration (70%) had the lowest infection ratio of cells, while the significantly highest spore count in a single bee was found in control bees (F 5 = 390.3, p < 0001, F 5 = 309.0, p < 0.001). These results suggest that the propolis may have toxic effects on N. ceranae spores, and could have potential use in disease management. Efectos de propó leos de abejas sin aguijó n en abejas asiáticas Apis cerana infectadas com Nosema ceranaeDebido a que Nosema ceranae causa mortalidad en las poblaciones de abejas de la miel tanto en colmenas manejadas como en el medio silvestre, muchos compuestos químicos han sido seleccionados y probados por su capacidad para suprimir las poblaciones de N. ceranae. Sin embargo, el uso de sustancias sintéticas ha dado lugar a residuos en las colonias y los productos de las abejas de la miel. El desarrollo de nuevos métodos para el control de la enfermedad de Nosema, es por tanto, muy necesario para los apicultores y científicos apidó logos. Se evaluaron los efectos de los propó leos de la abeja sin aguijó n Trigona apicalis, en abejas melíferas asiáticas Apis cerana infectadas por N. ceranae. Se inocularon individualmente abejas obreras de un día de edad libres de N. ceranae con 2 μl de solució n de sacarosa al 50% con 80.000 esporas de N. ceranae por abeja y luego se alimentaron con extracto de propó leo en agua al 50% y 70% (v / v). Todas las abejas tratadas con propó leos tuvieron tasas de supervivencia significativamente más altas que las abejas no tratadas (F 5 = 92,6, P <0,0001). Las abejas tratadas con la mayor concentració n de propó leos (70%) tuvieron la tasa de infecció n de célu-las más baja, mientras que el recuento de esporas en una sola abeja significativamente más alto se encontró en las abejas control (F 5 = 390,3, p <0,001, F 5 = 309,0, p <0,001). Estos resultados sugieren que el propó leos puede tener efectos tó xicos sobre las esporas de N. ceranae, y podrían tener un uso potencial en el manejo de enfermedades.

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