Microscopic X-ray technique can be used to map tiny insect organs

Scientists looked at insect breathing systems in detail using an imaging technique called X-ray micro-tomography. The scientists used the technique on living insects, to understand how their tiny organs change and grow over time.

In most studies, scientists examine the breathing tubes, or trachea, of dead insects. Unfortunately, these structures change after death, becoming filled with fluid, or even collapsing. This means scientists miss important insights into how these structures normally develop as the living creatures grow.

For this study, the researchers therefore wanted to capture images of living insects at different stages of growth. Specifically, they wanted to see if they could successfully measure the size and volume of the tracheal system in beetle larvae using X-ray micro-tomography.

They collected larvae of the long-horned beetle Cacosceles newmannii from sugarcane plantations in KwaZulu-Natal, South Africa. The larvae were kept alive in the lab and then anaesthetised (sedated) so that they could be scanned.  Using  X-ray micro-tomography, the researchers were able to scan the tracheal structures without harming the insects in the process.  

Researchers used the scans to map the respiratory structures, and to recreate them in 3D on a computer. They also showed that the insects could be anaesthetised and examined without affecting their later survival or development, something that has been a challenge in previous studies.

This is an important advance, since other researchers can now use the same approach to scan and model the organs of live insects, so that they can study how insects develop, grow and survive under different conditions.

Unfortunately, the researchers were only able to map tracheae over the size of 15 micrometres (15 µm). While this is still tiny in everyday terms, insect tracheae can be as small as 1 µm, meaning that even this approach may miss some important data. 

The size of the live larvae also meant that the researchers were unable to scan them in the best possible resolution.

They note however that the 15 µm size might be sufficient to get most of the detail in larger insects, and that future studies should explore how to improve resolution.

Cacosceles newmannii is an indigenous beetle species sometimes found in sugarcane plantations in KwaZulu-Natal, and a potential pest of these economically-important crops. 

Understanding the beetle’s biology may therefore provide much-needed clues for controlling the larvae in sugarcane crops. 

The study was a collaboration between scientists from South Africa and Sweden.

Abstract

Quantifying insect respiratory structures and their variation has remained challenging due to their microscopic size. Here we measure insect tracheal volume using X-ray micro-tomography (µCT) scanning (at 15 µm resolution) on living, sedated larvae of the cerambycid beetle Cacosceles newmannii across a range of body sizes. In this paper we provide the full volumetric data and 3D models for 12 scans, providing novel data on repeatability of imaging analyses and structural tracheal trait differences provided by different image segmentation methods. The volume data is provided here with segmented tracheal regions as 3D models.

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