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Xenopsylla ramesis is a flea species parasitizing gerbilline rodents in the deserts of the Middle East. This study was undertaken to determine metabolic requirements of the different developmental stages of the flea-life cycle as well as to investigate the metabolic response to temperature and starvation after blood feeding. A high resolution respirometry system was used to measure CO2 emission of fleas ranging in size from 0.166+/-0.006 mg (larvae) to 0.263+/-0.009 mg (adults). The free-living stages (larvae and adults) had significantly higher metabolic rates than the cocooned stages (pupae). CO2 emission rates of the larvae exceeded that of the adults by 2.6-fold and the pupae by 7.3 times. In the adults, both temperature and blood feeding significantly affected starvation-level metabolism. Metabolism was temperature dependent with an average Q(10) of 2.57 for females and 2.55 for males over the temperature range of 10-30 degreesC. No consistent decline in thermal sensitivity at higher ambient temperatures was evident. Fleas that had a blood meal prior to starvation had significantly higher metabolic rates (0.86 +/- 0.008 x 10(-3) ml mg(-1) h(-1)) than fleas, which were newly emerged unfed adults (0.56 +/- 0.1 x 10(-3) ml mg(-1) h(-1)). Water content also differed between fed (range approx. 67-69% body mass) and newly emerged adults (range approx. 73-75% of body mass). Feeding may stimulate some as yet undetermined physiological process that causes differential metabolic response in starving, fed and unfed fleas. Characteristics of gas exchange in desert-dwelling fleas are reflective of the off-host life style in the protected microenvironment of the host nest or burrow, rather than as a response to any type of environmental extreme. (C) 2003 Elsevier Inc. All rights reserved.