7


_ , , While some strains—owing to their general charac-
teristics, and not owing to greater resistance of individual
bees to the parasite—are found to be fairly immune to
attack when managed in a rational manner, it must be
recognised that no strain is truly immune, and that com-


parative immunity is almost entirely a matter of manage-
ment.
; Where the older methods of beekeeping obtain
disease must be expected, but with Rational management
the modern strains of American Italian bees can be kept
free from the complaint.
During the course of the investigation referred to—
the results of which are published in Bee World, December,
I92I—it was observed : —


(i.) That British blacks, or Natives, and dark hybrid
bees are generally found to be infected with the
disease, and the infection to be in a well
advanced stage in the majority of cases. That
when these strains become infected treatment is
usually found ineffective owing to the low
prolificacy of these queens compared with those
of high grade Italian strains.
(ii.) That while stocks of Italian strains of bee
headed by high grade and prolific queens are
usually found to be free from infection, some
cases of infection are found usually in the
initial stages. In these cases the cause is
generally to be found on examination of the
previous history of the colony.
(iii.) That the degree of infection found is dependent
on the age of the adult bees of the colony.
(iv.) That measures which increase the age of the
bees of a colony, such as the removal of brood,
the use of non-prolific queens, prolonged queen-
lessness, &c., render the colony open to attack
by the disease, and when infection has occurred
render the rapid spread of infection certain.
