Main immune defences of the honey bees are the cellular responses represented by phagocytosis and melanisation. There are a number of factors that could impact on the honeybees immune system and, therefore, increase their susceptibility to disease and lower their survivorship such as: exposure to pesticides, in air, in pollen, in nectar and in water; fungicides from both field and in-hive treatments; varroacides; the pest Varroa destructor; antibiotics used in in-hive treatments; fungal pathogens such Nosema apis and the emerging Nosema ceranae (Botías et al., 2013); bacterial and viral infections. More important, it must be highlighted the interactions among different chemicals and their synergic effect with diseases in the immune suppression of individuals and on the colony. The present study use simple and reliable methods that can clearly describe the state of health of the bees (Gonzàles-Santoyo & Còrdoba-Aguilar, 2011; Pandley & Tiwari, 2012), such as total hemocyte counts (THCs) and the activities of the plasmatic phenoloxidase (PO) and its inactive form (proPO) to assess the immune competence of individuals. Specimens of Apis mellifera ligustica were collected from beehives located in S. Giovanni (Trieste, “control site”) and from hives placed in Domio (Trieste, “polluted site”) in summer and early autumn. Both in summer and in autumn the statistical comparison showed a greater number of circulating hemocytes in bees from the site of Domio (July: 1159333.3±123073.60 - mean ± SE, n = 15; October: 813333.3±50583.89 - mean ± SE, n = 15) compared to the numbers recorded in bees from S. Giovanni (July: 834166.7±55493.08 - mean ± SE, n = 12; October: 273333.3±33046.38 - mean ± SE, n = 12). The statistical analysis showed a trend towards significant difference in July (Wilcoxon rank sum test, p = 0.063) and an highly significant difference in October (Wilcoxon rank sum test, p < 0.00001). The honeybees from Domio presented an highly significant lower PO activity than those from S. Giovanni (ANCOVA: F3,206 = 38.73, p < 0.01, nS.Giovanni = 17, nDomio = 18). Also with regard to the enzymatic activity of the proPO we recorded a significantly higher one in the honeybees from S. Giovanni in comparison to those from Domio (ANCOVA: F3,206 = 23.66, p < 0.01, nS.Giovanni = 17, nDomio = 18). It should be noted that 52% of the bees collected from hives of Domio had 1 or 2 individuals of Varroa destructor on the tergites of the thorax. The higher activities of PO and proPO in the honeybees from S. Giovanni site is probably to be ascribed to the different quality of the environment in the 2 sites and thus it indicates a depression of non-specific immune competence and an increased susceptibility to Varroa destructor parasites in the honeybees from Domio.
