[Differences in the blocking of the proventriculus in male and female Xenopsylla cheopis (Siphonaptera: Pulicidae)].

Frequency of block formation was studied in Xenopsylla cheopis infected with the triptophan-dependent and the typical strains of Yersinia pestis from the Mountain-Altai natural plague focus. It was shown that the rate of blocked males in comparison with that of females was statistically higher. In experiments with the triptophan-dependent strain the frequency of blocking in males was 40.9% and exceeded that in females at four times. The highest rate of blocked males was marked at 7-10th and that of females at 21st days. The tryptophan-dependent strain did not concede to the typical strain in the ability to form a proventricular block in fleas.