Production of sterilized pupae and flies

At the Bio-Fly facility, we produce sterilized male Mediterranean fruit flies (Medfly) used to control the Medfly based on the Sterile Insect Technique (SIT).

The strain of flies we produce is Vienna-8, and was developed by the Entomology unit of the FAO/IAEA in Vienna. This strain has unique genetic attributes that allows separation of males from females, thus enabling release of only sterile males into the fields.

Vienna-8 strain females are much more susceptible to heat than their male counterparts. During the production process, we utilize this sensitivity and conduct thermal treatment in order to eliminate female embryos and produce exclusively male pupae. In addition, in this strain it is possible to distinguish between males and females at the pupae stage due to the different colors of the pupae (females – white, males – brown).

Bio-Fly's facility has two main production lines:

• Colony – breeding of males and females for the production of large quantities of eggs.
• Male only – exclusive production of males for release in the field.

Rearing is carried out in several stages in 20 breeding rooms, each with unique climatic and lighting conditions in accordance with process requirements.

Egg Production

Egg production is executed in the sandwich model oviposition cages. The cage screens are made of a fine net, through which the females insert their ovipositor and lay chains of eggs into a water bath at the bottom of the cage, from which eggs are collected every 24 hours. 

After collection, eggs undergo incubation. The eggs designated for the Male Only line undergo thermal treatment during which the female embryos are eliminated.

Larvae rearing

Close to the time of their hatching, the eggs are placed on a bedding of artificial nutrients in rearing trays, that are places one atop the other in columns of up to 30 trays.

The larvae that hatch from the eggs are fed for several days by the artificial nutrient bedding and develop on it. When they are ready for pupation, they jump off  the bedding trays. This stage corresponds to their jumping off the fruit in nature. The larvae are collected every 24 hours.

Pupation and pupae maturation

The larvae collected are moved inside trays with pupation bedding (sawdust or vermiculite) into a room that is dark, dry and cold – for pupation. Within several hours, the larvae begin to transform into pupae.

About 24 to 48 hours before the flies emerge out of the pupae, the following actions are taken:

• Colony pupae (male and female) are placed in oviposition cages to start a new growth cycle.
• Male only pupae undergo a process of packaging and irradiation

Packaging and irradiation

Male pupae are colored with florescent dye which will leave its stamp on the flies as they emerge. Thus, it is possible to differentiate between wild  and sterile flies during monitoring of field traps.

The dyed pupae are packaged in plastic vacuum bags which carry indicators. The bags are irradiated using a Gammacell 220 irradiator, at a rate of at least 100 Gy. Irradiation disrupts the spermatogenesis in the flies that will emerge from the pupae, without significantly damaging their vitality, or their ability to fly and copulate.

As a result of irradiation, the indicators on the bags change color, from white to blue, and this verification that the pupae were irradiated.

At this stage, there are two options for continuation of the production and supply process, depending on the product required by the customer:

Product A: Sterile pupae

Product B: Sterile flies prepared for ground dispersal

After irradiation, the pupae are inserted into paper bags, where the flies emerge within 48 hours. Over the next 4 to 5 days, the flies are fed by the nutrient bedding inside the bags. Later, they are shipped to the customer and dispersed in the field within several hours, sexually mature and ready for action.