Helox suggests advective ventilation of the insect tracheal system during discontinuous gas exchange

Waseem Abbas; Philip C. Withers; Theodore A. Evans

doi:10.1071/ZO25023

RESEARCH ARTICLE (Open Access)

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Helox suggests advective ventilation of the insect tracheal system during discontinuous gas exchange

Waseem Abbas

^A ^B ^* , Philip C. Withers ^A and Theodore A. Evans ^A

+ Author Affiliations

- Author Affiliations

^A School of Biological Sciences, University of Western Australia, Crawley, WA 6009, Australia.

^B Department of Entomology, University of Agriculture, Faisalabad 38040, Pakistan.

^* Correspondence to: waseem.abbas55@uaf.edu.pk

Handling Editor: Edward Narayan

Australian Journal of Zoology 73, ZO25023 https://doi.org/10.1071/ZO25023

Submitted: 6 May 2025 Accepted: 8 September 2025 Published: 25 September 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

About a century ago, Krogh theorised that gas exchange by insects between spiracles and tissues occurs by diffusion without an advective (convective) component but physiological data supporting the relative roles of diffusion and advection are unclear, especially for small, flightless insects that lack air sacs. We examined the role of diffusion and advection in gas exchange for the small red flour beetle (Tribolium castaneum; 1.5 mg; no air sacs) and the larger speckled cockroach (Nauphoeta cinerea; 700 mg; air sacs) by comparing spiracular cycle durations during discontinuous gas exchange in air and helox (21% oxygen in helium), which should increase diffusive but not advective exchange. Helox reduced the burst-phase duration of beetles by 13%, suggesting a substantial role for advection and a minor role for diffusion, challenging the theory that small insects rely on diffusion and consistent with evidence for advective gas exchange mediated by tracheal compression. For cockroaches, burst phase duration was unaffected, supporting a primary role of advection and unmeasurable diffusion. We conclude that helox may provide a novel and useful experimental approach to discriminate between tracheal diffusion and advection. A mechanistic understanding of tracheal gas exchange for the red flour beetle could facilitate development of physiologically informed fumigation regimes for pest management.

Keywords: controlled atmospheres, convection, DGE, diffusion, gas exchange, insects, Nauphoeta cinerea, Tribolium castaneum, stored grain insect pests.

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