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IAEA Advances in Genetic Sex Separation in Insect Pests Highlighted in New Publication

South American Fruit Fly

A first for the South America Fruit Fly, a colour based GSS has been developed through an IAEA CRP, in which males emerge from brown pupae while females emerge from black pupae. This distinction has the potential for more efficient and cost-effective SIT programmes. (Photo: C. Cáceres FAO/IAEA).

Damage from insect pests can threaten farmers’ livelihoods and harm international trade and global food security, with limits put on the movement of some crops to curb the spread of pests. But the burden of such pests can be slowed down, and, in some cases, completely eliminated through harnessing the power of nuclear techniques. The technique used requires the mass rearing of insects, which can become more efficient thanks to the new findings.

The IAEA, in cooperation with the Food and Agriculture Organization of the United Nations (FAO),  has been researching and improving the sterile insect technique (SIT) for the last 60 years to help countries combat diseases that insects carry. FAO estimates that between 20 and 40 per cent of crops globally are lost every year due to pests  ̶  accounting for roughly US $220 billion in lost revenue to farmers. As an environment-friendly form of insect population management, the SIT uses irradiation to sterilize male insects. The sterilized male insects are then released into target areas to breed with wild females  ̶  resulting in no offspring and minimizing damage to crops by insects, which may burrow into or ingest the plant.

The daily production and release of millions of sterile males that are healthy and can compete against wild males is key to a SIT programme’s success. Participants of a Coordinated Research Project (CRP), Comparing Rearing Efficiency and Competitiveness of Sterile Male Strains Produced by Genetic, Transgenic or Symbiont-based Technologies, have studied the challenges associated with this process and ways to overcome them. Resulting from the CRP, a collection of papers highlighting the achievements of the research has now been published.

Sex determination of the fruit fly

To ensure effective SIT programmes, insects must ideally be separated according to sex, which is a challenging and tedious task for many species. “The active component of the SIT are the male insects, and we have now been able to isolate and harness genetic selectable markers which can identify and discriminate males from females,” said  Konstantinos Bourtzis, a molecular biologist at the FAO/IAEA Insect Pest Control Laboratory. “With male-only releases, we can ensure that the SIT is more cost effective and efficient in suppressing a target insect population as females lay eggs in the crops.”

Over five years, CRP participants compared the efficiency of various technologies used to produce sterile male insect strains. The project involved 18 scientists from 13 countries who studied a range of technologies and sterilization capabilities.

A first in research on the South American fruit fly (Anastrepha fraterculus), the project was able to find a genetic marker and link it to the sex of the fly as a result of the development of a genetic sexing strain (GSS) (see What is a genetic sexing strain (GSS)?). The marker, black in females and brown in males, is observed at the pupal stage and can reveal the sex of the fly earlier than previously. Using this marker, the female pupae can be separated automatically from the males in a production facility, allowing only males to be sterilized and transported and released into target areas.

Now that there is a marker allowing sex separation at the pupal stage of the South American fruit fly, the next step is to evaluate the genetic stability and biological quality of the strain under mass-rearing conditions and to assess its efficiency under field conditions.

“In South America, for the implementation of a mass-rearing facility and field project, a GSS strain is crucial,” said José Salvador Meza Hernández, Deputy Director of the Genetic Sexing Laboratories within the Moscafrut Operating Program at the Inter-American Institute for Cooperation on Agriculture in Chiapas, Mexico and a principal researcher in the CRP. “The recent discovery of the pupal marker and its use for the construction of black-pupae based GSS has a great potential to increase the effectiveness and reach of the SIT in the region.”

Research continues in additional potential markers for the South America Fruit Fly which would allow sex separation at the pupal stage as well as in improving the genetic stability and refinement of GSS of various SIT target species. (Photo: Hernandez/IICA)

Towards stronger sterilized flies

Another key achievement of this project was refining strains to improve genetic stability. In doing this, males could have a given desired trait such as improved rearing efficiency, sex separation, genetic stability or mating competitiveness. These refinement efforts took place with the Mediterranean fruit fly (Ceratitis capitata), Mexican fruit fly (Anastrepha ludens), New World screwworm (Cochliomyia hominivorax), yellow fever mosquito (Aedes aegypti) and Asian tiger mosquito (Aedes albopictus).

“We need to mass produce males of high biological quality in a cost effective way for sterilization and release,” said Bourtzis. “They need to compete with wild males; if they don’t achieve this then we can’t suppress the target population.”  

A follow-up CRP is now in progress, focusing on the development of generic approaches for the construction of GSS. This research into GSS and the development of strategies to construct GSS will be assessed through the efficiency, applicability and transferability of GSS to a range of species. The achievements of generic approaches to GSS will then be evaluated through small scale tests for their application as part of SIT projects.

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