Development of an effective and practical egg collection method for mass rearing Natal fruit fly for an SIT programme

Natal fruit fly needs to be incorporated into the fruit fly SIT programme to create fruit fly-free areas.  For large-scale mass-rearing of this species, an effective egg collection method had to be developed as female flies do not readily lay through gauze screen, and in the process the larval rearing diet had to be refined.  This project was initially registered to develop a practical, cost-effective egg collection system.

Compact, versatile semi-large-scale adult fruit fly cages were designed and built.  A mother colony of Natal fruit fly was started in smaller perspex cages using Natal fly eggs from CRI laboratories in Nelspruit.  As Natal fly larvae have different larval diet requirements to Medfly, a carrot powder-based larval diet developed by the IAEA, Vienna, was used, with good results.

Information on other fruit fly species that also do not lay through gauze was obtained from overseas mass rearing facilities, and based on this and on discussions with these experts, various egg collection methods were designed and tested for Natal fly in both the small and larger cages.

Considering the need for practicality, the best egg collection method for Natal fly was found to be perforated 500 – 600 ml plastic containers (jars), unlined with filter paper, and with only water in the base (to prevent desiccation).  An attempt to further facilitate easy collection of the eggs by using one long perforated perspex tube placed through the cage was unsuccessful.

Although it was not part of this project’s objectives, a very effective and practical and productive larval diet for Natal fly based on locally-sourced ingredients has also been developed.