Biochemical and Physiological Studies of Certain Ticks (Ixodoidea). Uptake of Water Vapor by the Different Developmental Stages of Hyalomma (H.) dromedarii Koch (Ixodidae) and Ornithodoros (O.) savignyi (Audouin) (Argasidae)

Uptake of water vapor from the air was investigated in the different developmental stages of Hyalomma (H.) dromedarii Koch (Ixodidae) and Ormithodoros (0.) savignyi (Audouin) (Argas- idae) by exposing partially dehydrated, unfed ticks to different relative humidity (R.H.) conditions at 28 C. The ticks may gain water by absorption from the ambient atmosphere, lose it through evapora- tion, or maintain their weight. The lowest R.H. at which sorption of water vapor from the air can occur is the critical equilibrium humidity (C.E.H.). At hydrating humidities (those above the C.E.H.) the amount of water absorbed by the dehydrated ticks increased with the rise in R.H. At dehydrating humidities (those below the C.E.H.), the ticks continuously lost water. This water loss was either drastic or slight, depending on the resistance of the larval, nymphal, or adult stage to desiccation. It was drastic in the larval and nymphal stages of H. dromedarii, which could not resist desiccation, and slight in the adult stage of the same species as well as in all stages of 0. savignyi. The C.E.H. was lower in the younger developmental stage or instar and higher in the older ones of each species. Thus, for H. dromedarii the C.E.H. was below 75% R.H. in the larval stage and above 75% R.H. in the nymphal and adult stages. For 0. savignyi it was slightly below 75% R.H. for first-instar nymphs, slightly above 75% R.H. for second-instar nymphs, and 84% R.H. for third-instar nymphs and females. Tick longevity was dependent on R.H. and water loss. When both species of dehydrated adults with blocked spiracles were placed in an atmosphere with R.H. above their C.E.H., they were unable to absorb water.