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Insects can improve their desiccation resistance by one or more of (1) increasing their water content (2) decreasing water loss rate or (3) increasing the amount of water able to be lost before death Female Drosophila melanogaster have previously been reported to increase their resistance to desiccation after a desiccation pre-treatment and recovery but the mechanism of this Increased desiccation resistance has not been explored We show that female but not male adult D melanogaster Increased their resistance to desiccation after 1 h of recovery from a 3 to 4 5 h pre-treatment that depletes them of 10% of their water content The pre-treatment did not result in an increase in water content after recovery and there is a slight Increase in water content at death in pre-treated females (but no change in males) suggesting that the amount of water loss tolerated is not improved Metabolic rate measured on individual flies with flow-through respirometry did not change with pre-treatment However a desiccation pre-treatment did result in a reduction in water loss rate and further investigation indicated that a change in cuticular water loss rate accounted for this decrease Thus the observed Increase in desiccation resistance appears to be based on a change in cuticular permeability However physiological changes in response to the desiccation pre-treatment were similar in male and female which therefore does not account for the difference in rapid desiccation hardening between the sexes We speculate that sex differences in fuel use during desiccation may account for the discrepancy (C) 2010 Elsevier Ltd All rights reserved