Impact of seasonal variations on morphology and physiology of Apis mellifera Linnaeus

Abstract

An experiment was conducted to investigate the effect of seasonal changes on the morphological (corbicula, proboscis, forewing, and hindwing) and physiological (hypopharyngeal glands and differential haemocyte count) characters of Apis mellifera L. workers during autumn, winter, spring, and summer seasons in year 2021 and 2022. The study found that the maximum values for morphological parameters i.e., proboscis length, corbicula length, length and width of forewing and hindwing, and physiological parameters i.e., hypopharyngeal gland acini size (length, width and surface area) and counts of plasmatocytes and granulocytes were consistently obtained during spring season. Notably, the most substantial reduction in immune cell count occurred during winter. Furthermore, a constant pattern observed across all seasons, indicating a significant increase in the size of all morphological characteristics as bees transitioned from nurses to foragers. In contrast, nurse bees always have larger hypopharyngeal gland acini sizes compared to foragers in all seasons. The differential haemocyte counts indicated a prevalence of plasmatocytes in the adult bee haemolymph. However, as bees shifted from nursing to foraging, the percentage of plasmatocytes and granulocytes decreased, accompanied by an increase in pycnotic cells, which signify programmed cell death. Consequently, the spring season emerged as the most favorable period for the growth and development of worker honey bees. This season consistently showcased optimal morphological and physiological characteristics, underscoring its importance in the life cycle of Apis mellifera colonies.

Keywords

• Apis mellifera
• Hypopharyngeal gland
• Plasmatocytes