Field OPS & Areas
– Sterile MedFly
Sterile Medfly production
Depending on the time of the season, up to 14 million Medfly males per week are currently produced at the Fruit Fly Africa Medfly mass rearing facility. As continuous fruit fly production is needed, the facility works 7 days a week throughout the year. Most staff members have attended intensive 3-month training programmes in mass-rearing fruit flies at the IAEA’s research laboratories at Seibersdorf in Austria. The others have received on-site training by IAEA experts in mass-rearing fruit flies.
A specially developed ‘genetic sexing strain’ of Medfly (“VIENNA 8”) has been developed by the IAEA in Vienna for use in SIT programmes. This strain is characterized by the females having sensitivity to heat (the temperature-sensitive-lethal – tsl – gene), and the white pupae (wp) gene whereby female pupae are white and male pupae are brown. The tsl characteristic enables the production of only male fruit flies for the releases by eliminating females with a heat-treatment, and the wp characteristic enables the identification of males and females in the pupal stage. This technique saves rearing costs, as sterile female flies play no part in the SIT process, and furthermore, sterile females, if released, can still sting the fruit and cause infection by pathogens.
The genetic filter process – purifying the strain
When fruit fly strains selected for certain genetic characteristics are mass-reared for a long time, they tend to lose these characteristics due to genetic recombination to the ‘normal’ state. In the case of VIENNA 8 this would means unless the ‘bad genes’ are removed (filtered) from the rearing process, the production of males only for releases, and the white pupae/brown pupae characteristic would be steadily lost.
To prevent this, the colony is constantly purified by removing ‘wrong sex’ pupae (white males and brown females) in a separate filter unit. This process also automatically removes any females that become resistant to the heat treatment. The colony is thus constantly regenerated using the purified material, ensuring that the colony maintains its genetic integrity, and preventing the release of females into the field, even though they are sterile.
Following additional funding from government, the Fruit Fly Africa Medfly Facility in Stellenbosch was extended in 2009. The additional building will increase the production capacity to approximately 40 million sterile males per week.