Differential Effects of Photoperiod on Development and Reproduction in “Montane” and “Prairie” Strains of the Rocky Mountain Wood Tick (Acari: Ixodidae)

Abstract

Progeny of Dermacentor andersoni Stiles adults collected from one "montane" and two "prairie" sites in southern Alberta, Canada, were exposed to combinations of 9:15, 11:13 and 13:11 (L:D) daily photoperiods during various stages of their life cycle. Time required for developmental and reproductive events was recorded. Significant differences in mean molting times of fed larvae were observed, yet the differences were small, and mean times were not attributed to photoperiodic regime. Fed nymphal "prairie" ticks had significantly longer developmental rates under decreasing light regimes than in constant or increasing regimes, while "montane" ticks showed no differential response to any of these regimes. Engorged "montane" females in all regimes weighed significantly more than those in either "prairie" strain, and "prairie" strain females in increasing and constant short-day regimes were significantly heavier than those in decreasing and constant long-day regimes. Photoperiod is unimportant in the regulation of fed-larval development, and the magnitude of female engorgement may be nominally favored by short-day and increasing regimes. The differential phenotypic expression of photoperiodic regulation of fed nymphal development in this tick may have resulted from selective pressures involving differences in host availability and moisture conditions in the two geographic regions.

Winter-exposedAmblyomma americanumandDermacentor variabilisadults (Acari: Ixodidae) do not exhibit behavioral diapause

“…This tick began ovipositing between 12 and 26 April and the resulting eggs, similar in appearance to those observed for Argas reflexus (Dautel and KnOlle, 1998), were viable until 12 May. This ovipositional delay is characteristic of developmental diapause as described by Belozerov (1982), and in A. americanum (Pound and George, 1988), A. marmoreum (Fielden et al, 1992), A. triguttatum triguttatum (Guglielmone and Moorhouse, 1986) and D. andersoni (Pound and George, 1991). However, the ticks in this study that were fed outside or inside and returned to the laboratory showed no delay.…”

The Biological Survey of Canada: A Personal History

“…Wilkinson (1968) speculated that diapause may prevent nymphs, moulting from larvae late in the year, from feeding prior to overwintering. Similarly, Pound and George (1991) reported that nymphs from prairie strains of D. andersoni entered diapause more readily than montane strains. This behaviour would presumably be of adaptive advantage to minimise exposure to arid climatic conditions and periods of low host availability in the prairies.…”

Simulation of climate-tick-host-landscape interactions: Effects of shifts in the seasonality of host population fluctuations on tick densities

“…The interaction of delays in the occurrence of peak host densities with decreasing day length and temperatures further suppresses and delays tick population cycles by delaying the development of off‐host ticks. Decreasing day‐length and temperatures during fall reduce host‐seeking tick activity and initiate developmental diapause for winter survival in fed nymphs (Sonenshine and Levy , Pound and George ). Increasing day‐length and temperatures return host‐seeking behavior in surviving unfed nymphs and adult ticks during late winter to early spring, with the timing varying with latitude (Sonenshine and Levy , Hair and Bowman , Teel et al We parameterized our model to represent latitudes characterized by mild winters with periodic warm periods of three to five days (with daily maximum temperatures above 10° C), which can initiate host‐seeking activity.…”