Introduction:
Despite the increased rates of infestations with I. ricinus (Ir) and D. reticulatus (Dr) ticks observed over the last decade, no effective control methods have been developed so far. The resent study was focused on assessment of the action of pyrethroids on these both tick species.

Material and Methods:
The different doses of four pyrethroids, i.e. deltamethrin – D (K-Othrine), permethrin – P (Copex WP), cypermethrin – C (Kordon 10WP), and alphacypermethrin – AC (Alfasekt 5SC) were tested. The LD50 for each tested compound was also determined for both tick species. Unengorged and engorged (maintained on rabbit skin) tick females were sprayed with 20ml of 0.01563–0.50% solutions of the tested preparations.

Results:
The investigations showed that sensitivity of Ir and Dr to the tested pyrethroids, but the effects exerted by the different doses varied between both tick species and between engorged and unengorged females in these species. The strongest toxic effect on unengorged and engorged Ir and Dr females was exerted by D, whereas the effect of AC was weaker. The LD 50 (in µg/1 g b.w.) of D, AC, C, and P for unengorged Ir and Dr females was, respectively, 55.4 and 25.5, 105.2 and 48.5, 225.9 and 197.7, and 553.8 and 380.8. In the case of engorged Ir and Dr females, the LD50 of AC, D, C, and P reached a value of 0.9453 and 0.2310, 1.0428 and 1.3533, 3.489 and 6.5662, and 8.3955 and 7.3940, respectively.

Conclusions:
The differences between the effects of the tested pyrethroids and their different doses on Ir and Dr highlight the necessity for development of a strategy for control of the tick species in different regions, based on investigations of their sensitivity to chemical compounds.