The main immune defences of the honeybees
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 the air, pollen, nectar and 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; bacterial and
viral infections. More important, we highlight the
interactions among different chemicals and their
synergistic effects with diseases in the immune
suppression of individuals and on the colony.
The present study uses methodologies that can
describe the health status of the honeybees, such
as total hemocyte counts (THCs), 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 in summer and
early autumn from beehives located in S. Giovanni
(Trieste, “control site”) and from hives placed in
Domio (Trieste, “polluted site”). In both seasons
the statistical comparison showed a greater
number of circulating hemocytes in honeybees
from Domio compared to the numbers recorded
in those from S. Giovanni. The Domio’s honeybees
showed a lower PO and proPO activities than those
from S. Giovanni. It should be noted that 52% of
the bees collected from the hives in Domio had
one or two individuals of Varroa destructor on the
tergites of the thorax. The higher PO and proPO
activities recorded in the bees from S. Giovanni
site are probably due to the different quality
of the environment in the two sampling sites
indicating a depression of non-specific immune
competence and an increased susceptibility to
Varroa destructor parasites in the honeybees from
the polluted site of Domio.
