K. Gaede et W. Knulle, ON THE MECHANISM OF WATER-VAPOR SORPTION FROM UNSATURATED ATMOSPHERESBY TICKS, Journal of Experimental Biology, 200(10), 1997, pp. 1491-1498
The nascent salivary secretion of 41 partly dehydrated and unfed adult
female Amblyomma variegatum, 5-8 months post-ecdysis, during water va
pour uptake at 93.5% relative humidity and 20 degrees C, had an osmola
lity of between 298.6 and 769.7 mosmol kg(-1) (mean +/- S.D. 470.3+/-8
5.8 mosmol kg(-1)). This range would allow water vapour uptake at rela
tive humidities of approximately 98-99%, but it would not suffice for
lower relative humidities down to 80-85%, the critical equilibrium hum
idity of A. variegatum, At this relative humidity (85%), an osmolality
of 9796 mosmol kg(-1) is required for water vapour uptake, It is prop
osed that hydrophilic cuticle in the hypostome could play a role in wa
ter condensation and that the slightly hyperosmotic secretion of the a
granular alveoli of the salivary glands might alter the water affinity
at the adsorbing cuticle surface and release the adsorbed water, The
water-enriched secretion would then be drawn into the mouth by the pow
erful suction of the pharynx, This hypothetical hydrophilic cuticle co
mponent of water vapour uptake in A. variegatum merits closer investig
ation, The sorption kinetics of A. variegatum support an additional 'o
smotic' component of water vapour uptake at humidities near saturation
. A nanolitre osmometer particularly suited to sample volumes smaller
than 5 nl was developed. This device does not require the transfer of
fluid after collection, and its measurement range is extended beyond t
he 5 osmol kg(-1) that can be measured using commercial apparatus.