A water balance study was conducted on newly-emerged adults of seed beetle, Callosobruchus maculatus, to explore how South India strain survives longer than Brazil strain in laboratory cultures. No difference between strains was noted with regard to dehydration tolerance, and water conservation features confirm classification of this species as xerophilic. There was no evidence for critical transition temperature (CTT), thereby safeguarding against excessive water loss as the temperature rises, or for critical equilibrium humidity (CEH), indicating that water is imbibed as a liquid. In contrast to the Brazil strain, adults of the South India strain were distinguished by a larger body size, resulting in a lower net transpiration rate with suppressed activation energy (Ea, permeability constant) for water loss, and a lower percentage body water content due to a higher dry mass (fat). These modifications for water balance of the South India strain link enhancing time for reproduction and distribution spread in the adult with the higher seed consumption/respiratory rate trait that has been previously reported for larvae of this strain.
Dehydration of Onymacris unguicularis (Haag) for 10 days at 27°C resulted in a weight loss of 14.9%, and a 37% decrease in haemolymph volume. Although there was an overall decrease in the lipid content during this period, metabolic water production was insufficient to maintain total body water (TBW). Rehydration resulted in increases in body weight (6.2% of initial weight), TBW (to normality), and haemolymph volume (sub-normal at the end of rehydration). Despite an increase of 44.0 mg in the wet weight of O. unguicularis after drinking for 1h, there was little change in the water content at this time, although the total lipid content increased significantly. Increases in haemolymph osmolality, sodium, potassium, chloride, amino acid and total sugar concentrations during dehydration were subject to osmoregulatory control. No evidence of an active amino acid-soluble protein interchange was noted during dehydration or rehydration. Haemolymph trehalose levels were significantly increased at the end of rehydration (relative to immediate pre-rehydration values), indicating de novo sugar synthesis at this time. Osmotic and ionic regulation was evident during rehydration, but control of OP during haemolymph-dilution is poor and accomplished largely by the addition to the haemolymph of free amino acids and solute(s) not measured in this study. There was little mobilization of sodium and chloride ions from storage sites at this time. The lesser osmoregulatory ability of Onymacris unguicularis and perhaps earlier susceptibility to osmotic stress, a significantly high normal blood glycerol level (relative to other diurnal adesmiine tenebrionids), and a water storage mechanism associated with synthesis of fat, probably all contribute to the development of fog-basking behaviour in this species. Water gain in O. unguicularis during periods of relative drought is probably largely accomplished by a greater food consumption.