Introduction:
introduction. Ixodes ricinus tick is of great medical and veterinary importance and has a wide range of geographical distribution. The study presents the effect of permethrin (Per) and cypermethrin (CM) on engorged I. ricinus females.

Material and Methods:
The effect of perythroids studied on engorged I. ricinus females was assessed on the basis of the pre-oviposition and oviposition period. Remote effects of Per and CM application were assessed by investigation of the length and course of embryonic development and larval hatching from eggs laid by pyrethroid-treated females. Per (Copex WP) was used at doses of 0.78125–25.0 µg/1 specimen, and CM (Kordon 10WP) was applied at 0.3125–10.0 µg/1 specimen. Immediately after the feeding period, I. ricinus females were sprayed with 20 µl of a pyrethroid solution and kept at 28°C and 75%RH.

Results:
The experiments demonstrated that CM exerted a stronger toxic effect on I. ricinus females than Per. The lowest doses of CM doubled the length of the pre-oviposition period while its highest doses prolonged the period nearly three times compared with the control. The pyrethroids applied reduced the number and weight of eggs and changed the parameters of the oviposition process. Application of the tested pyrethroid doses led to disturbances in the embryonic development of I. ricinus, i.e. the development was prolonged, few normal larvae hatched, numerous eggs and embryos at various developmental stages died, and larval hatch was inhibited.

Conclusions:
Knowledge about the sensitivity of engorged females to different doses of the tested pyrethroids and the remote effects of their action can be used in practice for tick control among livestock animals, and the reduction of tick population abundance in the environment.