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Breakthrough IAEA Infrared Imaging Research Reveals Insect Development in Chrysalis


28-day old tsetse fly pupa under 950 nm NIR illumination. (Photo: Z. Moran/IAEA)

No one in the history of studying insects had ever observed fly pupae without first physically breaking their shells. That was until last month, when researchers at the IAEA and the Food and Agriculture Organization of the United Nations (FAO) used near infrared imaging to allow continuous observation of the entire development process of living pupae without disruption.

“Entomologists have had to first break the outside shell and kill the insect,” said Andrew Parker, entomologist at the Joint FAO/IAEA Division. “But now, we can finally clearly see each stage of development using live insects.”

“No one had ever seen this before,” he added, describing when he first saw the pupa of a live tsetse fly displayed on a computer monitor. Parker along with Zelda Moran developed this new methodology and published their findings in the Journal of Insect Science.

The scientists developed this method of imaging to help them separate male and female tsetse flies as part of efforts to control the spread of sleeping sickness and nagana — two diseases tsetse flies carry that infect people and livestock in many areas of Africa. With this method, scientists can determine the sex of the flies while they are still contained in their protective pupal shells, making them easier to handle and less likely to die during the sorting process. This is an important part of a nuclear-based insect pest birth control method called the sterile insect technique (SIT).

SIT involves using ionizing radiation to sterilize separated male insects and then releasing them into nature where they mate with wild females, resulting in no offspring and, over time, reducing the overall insect population. Separating the males and females using the infrared imaging method helps to ensure only sterile males are released. Fewer insect pests mean less damage caused through the spread of disease or the destruction of crops. Through its technical cooperation programme, the IAEA makes this technique available to its Member States.

While the tsetse fly was the first insect to have its pupae development continuously monitored, the same method can also potentially be used to observe pupae of thousands of different kinds of insects, said Parker. “This discovery could lead to new applications in entomology, not just with the sterile insect technique, but in other areas such as monitoring infestations in fruits and plants.” This was emphasized in a recent article featured in Entomology Today.

How it works

Infrared is waves of energy that exist between waves of visible light and microwaves on a spectrum of energy. Its range of wavelengths is longer than visible light, which means it cannot be seen by the naked eye, but it exists everywhere to different degrees.

As the name suggests, the near infrared imaging technique uses wavelengths barely greater than visible light. A standard digital camera equipped with the infrared filter removed can detect the near infrared waves reflected or absorbed by an object: the more an area of the object reflects near infrared, the lighter that area appears. The differences in reflection are picked up by the sensor and result in an image. Scientists can use this technique to create time-lapse videos and photographs.

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