An Air-Flow System for Measuring Total Transpiration and Cuticular Permeability in Arthropods: Studies on the Centipede Scolopendra Polymorpha

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Abstract
An air-flow system (transpiration monitor) for measuring small and sporadic losses of water from intact arthropods and across isolated integument or artificial membranes is described and tested on the desert centipede Scolopendra polymorpha. Mean water loss rates (WLR) at 40 C (2.03 mg cm⁻² h⁻¹) were approximately three times those at 30 C (0.64 mg cm⁻² h⁻¹). The first hour's water loss at both temperatures featured numerous small bursts of moisture associated with oral discharges; peaks corresponding to these bursts decreased in amplitude and frequency during the second hour. Water loss increased in normal (unsealed), alive (mouth and anus sealed), and dead (mouth and anus sealed) centipedes as temperatures were gradually raised from 30 to 42 C; the lowest WLR over the entire temperature range was observed in alive-sealed centipedes. The permeability of a piece of untreated cuticle between 25 and 42 C was greater than its permeability after coating the same piece with 10 μg cm⁻² of the hydrocarbon, n-eicosane (C20). Comparison of the water relations of S. polymorpha with other arthropods as well as the potential and limitations of the transpiration monitor are discussed.