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. 
(v.) That vice versa, measures which decrease the 
average age of the bees of a colony, such as 
the addition of brood, stimulation for brood 
