Stainless Steel Awards 2008

Merit Award - Innovation Category

Pure Steel Products
Product: Stainless Steel Breeding Basket

The basket designed for Xsit eradicates the need to use pesticides by using a sterile insect release programme for the control of the False Codling Moth in citrus. The project has a huge environmental impact considering the amount of pesticides that will be replaced with this revolutionary natural pest control process. Founded in 1993 by LF Vorster, Pure Steel Products started with manufacturing stainless steel braai grids. It has since proven itself as a leader in  high quality stainless steel wire products for both domestic and industrial markets. All of its products are manufactured from stainless steel wire and electropolished to a superb finish. False Codling Moth, or Thaumatotibia Leucotreta (Lepidoptera: Tortricidae), is indigenous to southern Africa, the Ethiopian region and many islands on the African continent. It is the key pest of almost all citrus varieties in South Africa and is a serious pest in cotton and maize farming in tropical Africa. The moth has documented resistance to all chemical insecticides.

The moth is a serious citrus pest in the Western Cape, especially in the Citrusdal region, and causes major crop losses. However, it is due to the extreme phytosanitary hazard that this pest poses to the US citrus export programme, that the moth is feared and hated. The moth is currently not present in the US, which is an important market for South African citrus producers.

The solution to the moth problem was initiated by Xsit after intensive research revealed that the best answer to the problem was to create a Sterile Insect Technique (SIT) as an area-wide pest management tactic in South Africa and as an eradication tool should the moth be introduced to the US.

Studies into the radiation biology of the moth were followed by semi-commercial field trials. The potential for this approach to suppress the moth commercially, culminated in a ground-breaking decision by the South African citrus industry in 2006 to commercialise the Sterile Insect Technique for the False Codling Moth. As with other Sterile Insect Technique programmes internationally, the ability to mass rear and sterilise the insects were crucial steps in applying this technology. A rearing facility, or insectary, capable of producing more than 15 million insects a week was built in Citrusdal. 

The moth is reared on a special diet consisting of maize flour, wheat germ and milk powder, which is placed into 500ml glass jars that are then heat sterilised. After cooling, the jars are inoculated with moth eggs in an aseptic environment. The jars are closed with special lids, and incubated in larval rearing rooms at 26°C for larval development. After two weeks the larvae have matured and the jar lids are removed. The jars are turned on their sides to enable the larvae to leave the jars for pupation. The larvae spin their cocoons in the cells of honeycomb sheets made from polycarbonate plastic. The moths emerge from these cocoons 8 days later. About 12 million of these moths are gamma irradiated and released into citrus orchards every week to suppress feral populations of the moth. The balance of the moths is retained and the rearing cycle is repeated.

The 7 500 diet jars in the insectary are handled every day for up to 10 months of the year. The breeding cycle lasts for about three weeks tying up the equipment for that period. This means that 144 000 jars and 5 760 containers (each carrying 25 jars) are needed.

It is not productive or practical to manipulate each jar separately through the several stages of the rearing process. A system had to be devised to enable easier handling, maximise incubation space and facilitate manipulation of the jars through the various stages. It also had to be designed in such a way that a honeycomb sheet could be inserted below each container to assist pupation. A stainless steel box container was designed and a prototype was built. It immediately became apparent that the steel container and jars were far too heavy, created ventilation, temperature and humidity problems and were prohibitively expensive to manufacture.

However, proverbial gold was struck when the idea of a steel wire framework came up at 02:15am on a Sunday morning. Pure Steel tackled the problem and it was almost an anticlimax when it presented Xsit with the perfect container – a stainless steel wire basket. The basket consists of a 4.76mm wire framework with a notched level designed so that the flasks are positively located in a horizontal as well as vertical position. Each corner support was extended above the top frame of the basket so that it would positively locate the basket placed on top of it. Support bars were added to the base of the basket so that the special polycarbonate honeycomb collection mat could be inserted from one side of the basket. The sides of the basket were strengthened with support wires to form a strong, but still very light, construction, which will stand up to daily manhandling. Due to the space-frame design, less material was used, resulting in a cost-effective solution as well as a production efficient product. The basket and required tooling were designed in-house resulting in shorter delivery times.

Pure Steel’s Mario Vorster says: “We are proud to be associated with one of the greenest projects in the Western Cape.”