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 (F₅ = 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 (F₅ = 390.3, p < 0001, F₅ = 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.

The health of western honey bees (Apis mellifera L.) is constantly affected by Nosema ceranae, a microsporidian threat to colonies worldwide. We extracted propolis, a natural product exhibiting antimicrobial properties, from honey bee hives, fed it to worker bees before or after infection with N. ceranae, and determined its ability to protect bees from and treat them after infection. Protection from N. ceranae was tested using newly emerged bees that were group fed (50 bees/group) 50% propolis extract for 2, 4 and 8 d prior to infection with 1 × 10⁵ spores per bee. Treatment of N. ceranae was tested on newly emerged bees that were individually force-fed with 2 µL of 50% (w/v) sucrose solution containing 1 × 10⁵ spores per bee and then treated with 50% propolis in 50% sucrose solution (v/v) at 0, 2, 4 and 8 d post infection (p.i.). Positive (sugar water + N. ceranae), negative (sugar water only), and solvent (ethanol + sugar water) controls were included in both studies. Propolis fed to honey bees for 4 or 8 d before infection was associated with significantly reduced mortality, infectivity, and N. ceranae infection rates compared to the positive controls. Moreover, providing propolis to infected honey bees at d 0, 2, and 4 p.i. significantly reduced bee mortality, infection, and infectivity rates compared to the positive controls and bees treated 8 d p.i. Therefore, propolis extracted from honey bee hives may be a promising alternative approach to antibiotics for protecting colonies from Nosema disease. Graphical Abstract

There are multiple feedback mechanisms involved in appetite regulation, which is an integral part of maintaining energetic homeostasis. Older forager honey bees, in comparison to newly emerged bees and nurse bees, are known to have highly fluctuating hemolymph trehalose levels, higher appetite changes due to starvation, and higher octopamine levels in the brain. What remains unknown is if the hemolymph trehalose and octopamine levels interact with one another and how this varies as the bee ages. We manipulated trehalose and octopamine levels across age using physiological injections and found that nurse and forager bees increase their appetite levels due to increased octopamine levels in the brain. This is further enhanced by lower trehalose levels in the hemolymph. Moreover, nurse bees with high octopamine levels in the brain and low trehalose levels had the same appetite levels as untreated forager bees. Our findings suggest that the naturally higher levels of octopamine as the bee ages may result in higher sensitivity to fluctuating trehalose levels in the hemolymph that results in a more direct way of assessing the energetic state of the individual. Consequently, forager bees have a mechanism for more precise regulation of appetite in comparison to newly emerged and nurse bees.

Hypopharyngeal glands of honeybee are age-dependent structures that change with the size of acini and are correlated with various social behaviors. The histochemical structure ofApis ceranaandA. melliferaworker hypopharyngeal glands in four different developmental stages wes stained with ninhydrin Schiff's and periodic acid Schiff's reagents (PAS) for localization of proteins and carbohydrates, respectively, and examined with light microscopy. Nurse bees of both honeybee species had significantly larger glands as compared to guards and forgers, but there were no statistically significant differences between these two species after accounting for caste. Gland protein concentration increased progressively in nurse bees, and this was correlated with the appearance of enriched protein granules in the cytoplasm. In addition, the hypopharyngeal gland protein concentration ofA. melliferawas higher than that ofA. ceranaeven though gland size was not significantly different between species. However, gland size was shown to have decreased progressively in foragers and guards.