[Possible causes determining the developmental rhythm of populations of the nasopharyngeal gadfly of sheep, Oestrus ovis L. (Diptera, Oestridae)].

On the basis of observations undertaken in Azerbaijan and available literary data the author considers the hypotheses concerning the reasons causing the delay of the Ist instar larvae development and determining the age structure changes in population of Oestrus ovis L. within a year. The main reasons are as follows: factors depending on the population density at the larval phase, the light day duration within the life cycle of the botfly females.