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

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Posted by Tshego Chilume @tschilume

When you live in an arid environment with temperatures that can go up as high as 47^oC the prospect of the introduction of any tree into your area is music to your ears. This was the case for the people of Kgalagadi Desert when Prosopis juliflora and Prosopis grandulosa were introduced into the desert to control desertification and the constant moving sand dunes. For the first time large trees were seen around the district and communities had natural shade, fodder for their livestock and kids had playgrounds covered from the scorching sun. It was all merry; what could go wrong in such a beautiful scene? You would think nothing!

Except Prosopis is one of the worst invasive plant taxa in the world, it is capable of eradicating all woody plant species in its invaded habitat. Because there wasn’t much woody vegetation in Kgalagadi District, I figured there was no need to worry, however Kgalagadi Desert is known for its shrubs, cactus and grasses that have adapted to the harsh environment of their native ecosystem and are a valuable source of water and food for the locals, their livestock and wildlife. Forty years ago, the introduction was apparently met with dancing, celebrations and slaughtering of cattle (something Batswana do a lot when they have something to be happy about). But as time went on, a massive commotion has started between the relevant government agencies and communities. The impact of Prosopis is becoming increasingly apparent and difficult to ignore and everyone needs someone to blame for this. Prosopis is perceived to have caused the loss of native grasses, shrubs, reduction in borehole water yields, poisoning livestock and causing allergies to people. The communities blame the department of forestry for the introduction, forestry blames political pressure while the politicians blame the communities for insisting on a quick solution and the department of forestry for not doing enough research prior to the introduction.

The situation is that a solution to this social unease was necessary and back then there was very little funding available for research in issues of environmental issues. Even today, funding for research in environmental issues comes from donors outside Botswana. While this bickering continues, the impacts of Prosopis in Botswana have never been quantified and the current control practices were brought about by the public outcry.

This brings me to my current research on quantifying the ecological impacts of Prosopis juliflora in Gantsi District, the most ecologically and economically valuable district of Botswana. Gantsi district is home to one of the largest wildlife management areas in the world, Central Kalahari Game Reserve and in close proximity to the Okavango Delta (a world heritage site). This research will provide the impacts associated with Prosopis juliflora on the soil chemical variables and vegetation of Gantsi District. The research will improve our understanding of the effects of Prosopis and enable government to make informed decisions on the control measures and development of Prosopis management programmes.

Tshegofatso Sputnik Chilume is an MSc student in the Centre of Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. She is supervised by Cate Macinnis-Ng and Keotshepile Kashe (Okavango Research Institute, University of Botswana) quantifying the ecological impacts of Prosopis juliflora in Gantsi District, Botswana.