Geographic variability of morphogenetic diapause in larvae and nymphs of the taiga tick Ixodes persulcatus (Acarina, Ixodidae)

Abstract

The critical day length inducing morphogenetic diapause in engorged larvae and nymphs of the taiga tick Ixodes persulcatus Schulze, 1930 was shown to vary with both latitude and longitude. Intraspecific differences in ecological responses of larvae and nymphs to the day length were most pronounced in the latitudinal direction. The critical day length was 13.5–14.5 h in the southern part of the species range (40–43°N) and up to 18–19 h in its northern part (62°N). Longitudinal variation is closely linked to the severity of the climate increasing from west to east. It was demonstrated for the first time that mass diapause induction in nymphs may occur not only during the period of decreasing day length but also during the summer solstice, the latter variant being observed only in the sharply continental climate of Eastern Siberia. Adaptive advantages of this photoperiodic response under the conditions of a short summer are discussed. Diapause in ticks occurs in response to environmental factors, such as changes in the photoperiod, and represents the main adaptation by which ticks synchronize their activity with biotic resources.