Evaluation of the effect of various concentrations of selected pyrethroids on the development of Dermacentor reticulatus eggs and larvae.

The Palearctic three-host species Dermacentor reticulatus contributes to the circulation of numerous pathogens in the environment. Reduction of its abundance may therefore decrease the risk of tick-borne diseases in a given area. The aim of the study is to determine the effect of various concentrations of three pyrethroids--(D), cypermethrin (C), and alpha-cypermethrin (AC) on the development of D. reticulatus eggs and larvae. 217 engorged D. reticulatus females were examined in the investigations. After the feeding period, they were sprayed with 0.015625%, 0.03125%, 0.0625%, and 0.125% solutions of D, C, and AC, and kept at a temperature of 25 o C and 90% relative humidity throughout the preoviposition and oviposition periods. Eggs laid by females were kept in the same conditions until larval hatch. Based on the results obtained, parameters of the course of maturation and oviposition, as well as parameters of embryonic development, were determined. The investigations showed that the pyrethroids tested prolonged the egg maturation period, reduced the number and weight of eggs, and caused disturbances in embryogenesis in D. reticulatus. Upon treatment with as little as 0.015625% AC, larvae did not develop and all eggs died 1-2 days after oviposition. C led to a decreased percentage of normal larval hatch--31.96%, 15.51% and 12.5%, respectively, after using three increasing concentrations (control 98.15%), and a high rate of egg and embryo mortality. The least detrimental effect on the D. reticulatus maturation and embryonic periods was exerted by deltamethrin (82.74%, 84.37% and 16.80% of normal larvae in treatment with the three concentrations). Morphological anomalies were observed in larvae during the experimental period. AC appeared to have the most toxic effect during the maturity and egg development periods, while C exhibited lower toxicity. Application of these pyrethroids in engorged D. reticulatus females exerts distant effects that lead to substantial reduction of tick offspring abundance.