[Organization of acaricidal treatments in two districts of the Irkutsk Region].

In the Irkutsk suburbs (a relatively southern area of the Irkutsk Region of the nosoarea of a natural tick-borne encephalitis focus), Ixodes persulcatus imagoes begin its activity in the first 10 days of April and usually finishes it in September. In 1996-2006, there was a trend for an increase in the number of the tick's bites in human beings, as well as three-year cycles of fluctuation of this index. In the Bratsk suburbs (a relatively northern area), the imago becomes active only in late April and the last sticking cases usually take place in late August. In 1996-2006, there was no increase in the number of tick attacks of the population, but the cycle period of this index being longer than in the Irkutsk suburbs. It has been earlier recommended that two all-round antitick treatments using cipermitrine-based compounds should be made in the area of epidemiologically significant objects in the Irkutsk suburbs in late April and in the third 10 days of May. It is sufficient to perform one treatment in the Bratsk suburbs in the third 10 days of May.

[Change in sex ratio of a Drosophila population in relation to population size]. / Izmenenie polovogo sostava populiatsii drozofily pri dinamike cheslennosti.

Changes in sex ratio with population size fluctuations were studied in natural and cage populations of Drosophila. It was shown that the proportion of females decreased with an increase in population size both in natural and laboratory populations. If laboratory populations were maintained on a poor diet, this effect was absent. The amplitude of number fluctuation was shown to be higher in males than in females. The possible role of density-dependent selection on sex in the control of population size dynamics is discussed.