COMPOSITION of hemocytes and catalase activity in HONEY BEE (Apis mellifera L.) under DURING wintering
In the recent years, the number of honeybee colonies are decreasing worldwide especially after the winter season. Winter resistance of bees represents a complex of cellular and metabolic mechanisms. Particularly, activities of the immune and antioxidative systems play a key role in the organism protection against biotic and abiotic stresses. In insects, the success of the immune response depends on the composition of hemocytes, which vary with age, season and health condition of bees. Also, detoxification of reactive oxygen species (ROS), which are generated in excessive amounts upon stress, represents an important component of the protective mechanisms. The turnover of ROS is regulated by the antioxidative system, which includes numerous enzymes. Among them, catalase (CAT) represents the main enzyme, which breaks down hydrogen peroxide. Accordingly, the aim of our study was to evaluate the cellular composition of hemolymph and the activity of catalase in honeybees cultivated in Chernivtsi region of Ukraine under wintering conditions.
In winter (December – February) the hives were placed in a room with a constant temperature of 2°C. The temperature within the hives was 4°C. For experiments, 100-, 120-, 140- and 155-day-old worker bees were used. Composition of haemocytes was evaluated microscopically after a Giemsa staining. Activitiy of CAT was measured according to Aebi in (i) hemolymph and in tissues of (ii) head and (iii) thorax.
It was found that hemolymph [A1] of the studied bees contains prohaemocytes, oval plasmatocytes, spindle-shaped plasmatocytes, permeabilized cells, plasmatocytes with filopodia and oenocytoids. In haemolymph of 120-day-old worker bees the content of plasmatocytes with filopodia decreased compared to 100-day-old bees; in 140-day-old bees the content of prohaemocytes significantly increased, the content of spindle-shaped plasmatocytes decreased, whereas no essential changes were observed for permeabilized cells. Generally, the most essential changes in cellular composition of hemolymph were discovered in 140-day-old bees.
In the heads of 120- and 155-day-old and the toraces of 155-day-old bees the activity of CAT increased twofold as compared to 100-day-old bees. In contrast, the activity of CAT in the hemolymph did not change significantly during our experiment. Hence, changes of CAT activity in winter demonstrate a tissue-specific activity pattern.