Dehydration tolerance in relation to short day length in nonfed Amblyomma maculatum Koch, 1844 ticks (Acari: Ixodidae)

Ticks utilize a variety of strategies to mitigate water loss and enhance their off-host survival. This is the first report of a primarily tropical zone tick, the Gulf Coast tick Amblyomma maculatum, vector of Rickettsia parkeri, to regulate water loss by photoperiodic induction. Under short-day conditions (10h:14h L:D), water loss rates are decreased. This has a positive effect on survival by extending the time it takes to reach the dehydration tolerance limit. When cycled between long- and short-day conditions, the water loss rate drops and then returns to a faster rate after re-entering long-day conditions; this can occur quickly (within a day), multiple times, and in more than one life history stage. The decrease in water loss is more pronounced in immatures than adults. The percentage body water content, dehydration tolerance limit and critical equilibrium humidity are independent of photoperiodic changes. We conclude that any nonfed stage is adapted for survival by enhanced water conservation when the day length shortens.