Scientists Identify Gene Behind Key Sex-Sorting Trait in Fruit Flies for Pest Control

In a breakthrough that promises to transform pest management worldwide, an international team of researchers led by Justus Liebig University Giessen (JLU) in Germany and the Joint FAO/IAEA Centre of Nuclear Techniques in Food and Agriculture has finally identified the long-sought gene responsible for temperature-sensitive lethality (tsl) in the Mediterranean fruit fly (Ceratitis capitata)—a vital trait used in the Sterile Insect Technique (SIT).

This discovery fills a critical knowledge gap that persisted for more than 35 years, laying the genetic foundation for expanding this insect sex-separation technology to other pest species affecting agriculture, veterinary health, and human well-being.

The Science Behind SIT and the Role of TSL

The Sterile Insect Technique (SIT) is a targeted pest control strategy that involves mass-rearing insects, sterilizing them using radiation, and releasing sterile males into the wild. When these sterile males mate with wild females, no offspring are produced, gradually reducing pest populations. The method is species-specific and environmentally friendly, making it a key alternative to chemical insecticides.

A major breakthrough in SIT came in the late 1980s with the discovery of a temperature-sensitive lethality mutation—known as tsl—by researchers at the Joint FAO/IAEA Centre. This trait allowed for genetic sexing, in which female embryos die after a brief heat treatment, enabling only male insects to survive for use in field releases. The approach was revolutionary, allowing industrial-scale production of sterile males while avoiding the costs and inefficiencies of releasing sterile females.

Yet for over three decades, the exact genetic cause of the tsl effect remained elusive, limiting its application to species like the Mediterranean fruit fly, despite the broader demand for similar control in other pests.

The Genetic Breakthrough: LysRS Mutation

Now, thanks to sustained international collaboration and molecular research, the team has successfully pinpointed the tsl mutation as a single-point change in the Lysyl-tRNA synthetase (LysRS) gene. This gene is conserved across many insect species, making the discovery highly significant for broader pest control strategies.

By introducing the mutation into wild-type fruit flies, researchers confirmed that it produced the same temperature-sensitive lethality, validating LysRS as the responsible gene.

“This discovery is a true milestone,” said Kostas Bourtzis, molecular biologist at the FAO/IAEA Joint Centre. “After more than 35 years of research, we now have a precise molecular handle on temperature-sensitive lethality. This opens up the possibility of expanding genetic sexing systems to a wide range of insect pests with agricultural, veterinary, and medical relevance.”

“With the identification of the tsl gene, we are closing a major knowledge gap,” added Marc F. Schetelig, professor of insect biotechnology at JLU and liaison officer at the new Liebig Centre for Agroecology and Climate Impact Research, which was recently designated an IAEA Collaborating Centre in May 2025.

Implications for Global Agriculture and Public Health

The ability to genetically engineer tsl-based sex separation into other insect species offers a paradigm shift in pest management. It enables highly specific, sustainable, and chemical-free control methods for pests like:

• Tsetse flies, which transmit sleeping sickness

• Mosquitoes, vectors of malaria, dengue, and Zika

• Fruit flies and moths, which cause extensive agricultural losses

Such technology will be especially important in developing nations where agriculture is a primary economic sector and where chemical control poses risks to human and environmental health.

The tsl gene discovery also facilitates the use of precision genome-editing tools such as CRISPR-Cas9 to develop custom genetic sexing strains, streamlining the scale-up of SIT programs across diverse ecological zones.

A Strategic Partnership in Biotechnology Innovation

The study reflects decades of collaborative research between JLU and the Joint FAO/IAEA Centre, a partnership recently institutionalized with the launch of the Liebig Centre for Agroecology and Climate Impact Research as an IAEA Collaborating Centre. This alliance will now drive global efforts to develop new biotechnological tools for sustainable pest control.

“This paves the way for highly specific and sustainable insect control strategies without the use of chemical insecticides,” noted Schetelig. “It’s a leap forward in environmentally responsible agriculture.”

With the molecular mechanism of tsl now fully identified, scientists can confidently pursue the next generation of SIT-compatible strains, adapting the technology for different species and environments to meet the growing demand for resilient, green pest management strategies.