Moisture requirements for activity/survival of the gulf coast tick,<i>Amblyomma maculatum</i>Koch (Acari: Ixodidae), based on a water balance study of all life cycle stages

Abstract

Abstract To provide information pertaining to features fundamental for survival, activity and spread of the Gulf Coast tick Amblyomma maculatum Koch (Acari: Ixodidae), vector of agents of human spotted fever rickettsiosis (boutonneuse fever) and canine hepatozoonosis, we determined water balance characteristics for each life stage, supplementing earlier work on adults, for a more comprehensive evaluation through the life cycle. The water balance profile of A. maculatum follows a consistent developmental pattern where the egg is the major water-conservation stage, the larva emphasizes water gain (water vapor absorption from drier air; low critical equilibrium activity, CEA), the adult emphasizes water retention (low net transpiration rate) and the nymph is transitional. A. maculatum in the various stages shares a similar dehydration tolerance limit, CEA, percentage body water content and inability to drink free water from droplets with other ticks. The low net transpiration rate of A. maculatum is the distinguishing feature, classifying A. maculatum as xerophilic compared to other tick species and their corresponding stages. Of importance, the low net transpiration rate of A. maculatum does not match the humid environment (predicting high net transpiration rate) where this tick is distributed, rather it reflects conditions of the microhabitat and slightly altered behaviors relevant to drying out that permit survival in the larger areas that they occupy. Thus, the view that net transpiration rate is an indicator of habitat preference in terms of moisture requirements needs to be modified. Ticks operate on a smaller scale (i.e., microhabitat), indicating a need for direct field observations.