Posted by Jessica Devitt @Colette_Keeha

Over several millennia insects have developed physiological adaptations to their environments through the process of natural selection.  Thus, insects are one of the most diverse and widespread animal taxa.

Insects have evolved diverse respiratory responses to a wide range of environments. The mechanisms behind these differing responses are not fully understood, with some insects displaying adaptations to low O₂ (hypoxic) and high CO₂ (hypercarbic) atmospheres. One such adaptation is the so-called Discontinuous Gas Exchange Cycle (DGC) where the insect only releases CO₂ to the external environment periodically (Figure 1).

Figure 1. Graphic showing discontinuous gas exchange phases: The flutter phase (F) where CO2 is released during a rapid opening and shutting of the spiracle, the open phase (O) where a burst of CO2 is released from the spiracle and the closed phase (C) where the spiracle is closed for a time resulting in a small release of CO2 (Hetz & Bradley, 2005, p. 517).

There is debate as to what the main function of this adaptation is: one school of thought suggests DGC might protect against desiccation. The other is that DGC allows insects to withstand hypoxic environments.

This brings us to my study species: The golden-haired bark beetle (GHBB) (Hylurgus liginperda: Curculionidae). Bark beetles predominantly attack damaged trees, stumps and fallen/felled trunks and branches. GHBB adult beetles burrow through the bark creating galleries within the cambium/phloem, in which the eggs are laid. Once the larvae have consumed the available cambium/phloem and undergone pupation, newly emerged adults take flight to the next available resource.

Figure 2. Hylurgus ligniperda (Fabricius, 1792). (Schmidt, 2014)

Figure 3. Hylurgus ligniperda adults exposed under pine bark. (Pest Alert, n.d.)

The golden-haired bark beetle is a widespread forest pest distributed throughout several continents, such as Australasia and North and South America. Although the beetle itself does not cause significant damage to the heartwood, its presence on export logs creates a market access issue.

In my PhD study we will investigate the respiratory responses of GHBB to a range of atmospheric conditions, such as contrasting O₂/CO₂ levels over different durations. I plan to use GHBB as an experimental model to understand bark beetle respiration in the presence of low O₂/high CO₂ environments.  My experiments will manipulate atmospheric conditions with the addition of fumigants in order to ascertain the most effective conditions in which to treat export logs.

References

Hetz, S. K., & Bradley, T. J. (2005). Insects breathe discontinuously to avoid oxygen toxicity. Nature, 433(7025), 516-519. doi:10.1038/nature03106.

Pest Alert. (n.d.). Hylurgus ligniperda adults exposed under pine bark.  Retrieved from http://www.pestalert.org/espanol/PhotoDetail.cfm?RecordID=47

Schmidt, U.  2014. Hylurgus ligniperda. Retrieved from https://www.kaefer-der-welt.de/hylurgus_ligniperda.htm

Jessica Devitt is a PhD student at the Centre for Biodiversity & Biosecurity, School of Biological Sciences, University of Auckland and Plant and Food Research. She is researching the respiratory responses of the golden-haired bark beetle to advance fumigation techniques. She is supervised by Jacqueline Beggs from the University of Auckland, Adriana Najar-Rodriguez and Matthew Hall from Plant and Food Research