[Block formation in Citellophilus Tesquorum altaicus Ioff, 1936, fleas in relation to the sex of an insect].

Males and females of C. Tesquorum altaicus, the main vector of plague in its natural focus, were experimentally studied in different seasons (spring, summer) for their capacity of block formation. The experiments used 2 groups of fleas: the insects that have been infected in last autumn and hibernated and <<young>> insects, a that year's breeding. The investigations demonstrated that the hibernated fleas had insignificant differences (P>0.05) in the rates of block formation by sex in spring and early summer. Among the <<young>> fleas, a that year's breeding, the males with a gizzard block considerably exceeded the females in number (P<0.05) in July-August (a period of an intensified epizootic process in the focus). By seasons, the rates of block formation were 7.0 to 21.7% in males and 2.0 to 14.0% in females.