Adapting a gas chromatograph for use as a testing chamber for thermal ecology experiments

Authors: Zilnik, Gabriel; Casey, Miles; Merten, Paul; Machtley, Scott; Hagler, James

Submitted to: bioRxiv
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2025
Publication Date: 5/27/2025
Citation: Zilnik, G.L., Casey, M.T., Merten, P., Machtley, S.A., Hagler, J.R. 2025. Adapting a gas chromatograph for use as a testing chamber for thermal ecology experiments. bioRxiv. https://doi.org/10.1101/2025.05.22.655604.
DOI: https://doi.org/10.1101/2025.05.22.655604

Interpretive Summary: ARS scientists from Maricopa, AZ developed a novel use for an obsolete piece of laboratory equipment, a gas chromatograph. This equipment will be used to study how heat affects insects. The new design spins the insects in small tubes, making it easier to see when they get too hot to move properly. The device was tested on a predatory beetle in AZ cotton. The beetles could handle very high temperatures before getting too hot to function. After being in extreme heat, they ate fewer pest eggs. This recycled machine is much lower cost than new equipment and helps scientists study how insects react to high temperatures.

Technical Abstract: 1. Temperature impacts many aspects of species biology and ecology. A continuing struggle for studies in thermal ecology is accurate assessment of critical thermal maxima CTmax. Identifying when loss of equilibrium (LOE) occurs has been criticized for being too subjective. This is particularly true of small organisms, such as insects, where the loss of coordination can be difficult to observe. As such, ecologists have often used lack of movement as a proxy for LOE. 2. Here, we designed, tested, and present a guide to recycling surplus gas chromatographs for use as a thermal chamber that allows accurate and high throughput assessment of CTmax at relatively low cost. 3. We found the GC to be an adequate heating chamber for thermal experiments. Installation of a rotating rack that can hold glass observation vials allows for rapid identification of loss of equilibrium in subjects. We evaluated the CTmax of a common generalist predator in the Arizona cotton agroecosystem, Collops vittatus. Additional tests of static heat exposure also revealed that this chamber can be used for assessing the impacts of heat stress on predatory behavior. 4. We hope to encourage other ecologists to use this guide to recycle surplus laboratory equipment for use in thermal ecology studies. We believe that our thermal insect carousel can be used for CTmax, lethal temperature, and behavioral bioassays.