In the Egyptian and cemiolan races and the hybrid bees. the fresh weight in mg per head maintained its high level (record) during spring and summer compared to autumn season. Moreover, the fresh weight revealed higher estimates in the Camiolan and Hybrid bees than in the Egyptian race in all seasons. As for the dry weight. it has also been concluded that both the Hybrid and Camiolan populations. in all seasons exhibited higher estimates in relation to the Egyptian race. The measurements of fresh weight per thorax showed that all the three populations exhibited their highest estimates during summer season. In addition, both Camiolan and Hybrid bees were significantly superior to the Egyptian race in all seasons. A similar picture was detected in the thorox dry weight. Determination of nitrogen content per thorax showed that. the least significant differences between the three populations did not occur in spring and autumn. However the tested bees differed significantly during summer. The development of hypopharyngeal glands showed significant differences between the three populations. The Hybrid bees exhibited the highest development of these glands followed by the Camiolan and the Egyptian races- The esterase isozymes activities were assayed in healthy and infested pupal stages. While some esterases showed gradual decrease in activity followed by complete disappearance in successive pupal stages, others had highly active bands of isozymes in association with infestation of pupae by one or two varroa mites (Varroa jobsoni)