Wageningen, The Netherlands
January 22, 2003

A South African/Dutch cooperation is tackling the damage caused by insects in the cultivation of rooibos tea. The partners in the research project, which will run until the end of 2005, are Rooibos Ltd., ARC-Small Grain Institute, Plant Research International, Entocare and Syntech Senter, an
agency of the Dutch Ministry of Economic Affairs, will finance 60% of the project costs. Rooibos Ltd. expects an increase in demand for rooibos tea of at least 35% during the research period.

The insects causing the most damage in rooibos cultivation are very difficult to counter with pesticides. An effective control of these insects will lengthen the cultivation period by a year to six years and increase the annual yield. The growth in demand for organically cultivated tea demands new and efficient crop protection methods. The organisations are therefore especially oriented towards researching new organic control methods. Plant Research will contribute its know how and expertise in the field of aromatic substances.

Harmful moths
Two types of moths are primarily responsible for the damage to rooibos plants. The larvae from Isturgia exerraria (looper) feed on the plant needles, causing plants to reduce their yield. The other moth -
Monopetalotaxis doleriformis (clearwing) - creates the greatest problems. The larvae bore into the plant, thereby causing direct damage. More importantly, pathogenic fungi and bacteria can easily develop in the bored tunnels, causing indirect damage. Due to the dry conditions in which rooibos is grown, fungi and bacteria would have little chance of infecting the plant without these tunnels. The larvae themselves cannot be reached by natural enemies and insecticides. It is therefore crucial to develop control strategies that come into play before the larvae stage.

Pheromones and enemies
The partners are aiming to find natural enemies and pheromones (aromatic substances) to detect the moths, entice them into a trap or their behaviour. It is not possible to trace Monopetalotaxis doleriformis without digging up (and therefore destroying) the plants. Using pheromone traps, this moth can be detected at an early stage. This allows the best time for (conventional) control to be determined.

The Wageningen (NL) company Entocare will use the coming years for collecting, screening and breeding natural enemies of the rooibos pests that tackle the moths before they reach a dangerous stage. An example would be insects that eat the eggs of the moth.

Plant Research International will identify and apply the pheromones of the two rooibos moths. One of the most important techniques herein is electroantennography (EAG). The electric reaction of the moth's antennae to passing substances indicates what the insect can and cannot smell. The female moths produce the sex pheromone and thereby attract the males. Using the EAG technique, typical response generating compounds will be identified from extracts of female moths. These compounds can be detected by the males and may well be involved with the sex pheromone system.

TNO-Industrie in Eindhoven (NL) will formulate the selected compounds in a slow-release system. The Plant Research International PHEROBANK will produce the pheromone. It will then be necessary to test the synthesised substances in the field. Is it possible to attract the moths so that signalling and
removal or control becomes possible? Can the males be brought into such a state of confusion that they can no longer find the females?

Another part of the research will look at copying the fragrance of the rooibos plant itself. The expectation is that both males and (pregnant) females can be attracted by this 'aromatic bouquet'. Syntech in Hilversum (NL) will develop the ultra-sensitive EAG equipment required for this research.

Crop and economy
With around 300 associated growers, Rooibos Ltd. is easily the largest processor of this increasingly popular tea, which is reputed to have a calming effect. Rooibos belongs to another plant family than the well-known black tea. The plant only grows in certain South African soils, in which little else can be cultivated. The production method of the tea itself is identical to that of black tea.

Millions of people around the world drink rooibos tea. Its increasing popularity is illustrated by the rising export figures, although the largest group of tea drinkers are still in South Africa itself. A major increase in both production and export is anticipated in the coming years.