Healthy tomatoes thanks to wasps and fungal spores


Stefan Diener, Programme Officer at Biovision

An invasive species of moth from South America is threatening the livelihood of tomato farmers in Kenya. So many toxic substances have been used in the battle to control these pests that people are falling ill from their effects. However, the good news is that ecological alternatives are available.

Jacqueline Njogu (Minister of Agriculture for Kirinyaga County in Kenya) is worried. As well as having to deal with the usual insect pests, such as white fly, spider mites and thrips, local tomato farmers in her county have recently been fighting against another new and devastating pest: the tomato leafminer moth Tuta absoluta. This speciesarrived from South America and is now causing an annual loss of over 100,000 tonnes of tomatoes in Kenya – which is one and a half times as high as the total consumption of tomatoes in Switzerland every year. Out of desperation and a lack of knowledge about possible alternatives, the producers are resorting to ever stronger pesticides. As a result, they are not only poisoning the soil and beneficial insects, but (most seriously of all) also themselves; studies have demonstrated a link between the use of pesticides and loss of sight, liver damage, cancer, infertility and high rates of infant mortality, among other conse quences.

Serious gaps in knowledge

Jacqueline Njogu therefore arranged for a study to be carried out among the farmers in her county – and the results are shocking. Only a third of these farmers knew that they could protect their tomatoes from pests and diseases with different, more environmentally-sustainable measures as well as pesticide sprays… and just a quarter adhered to the safety instructions when they used pesticides and synthetic fertilisers.

Since the beginning of 2019, icipe, the International Centre of Insect Physiology and Ecology, a research institute based in Nairobi, Kenya, has been working on ways to combat the tomato leafminer as part of a Biovision project… with quite successful results! Dr Samira Mohammed and her team have identified a small species of parasitic wasp that lays its eggs inside the young larvae of Tuta absoluta which can significantly reduce the population of this pest in a natural way. Furthermore, they have also carried out research into a biopesticide based on an entomopathogenen fungus. This is a fungus whose spores infest the tomato leafminers and make them harmless. In collaboration with Real IPM, a Kenyan manufacturer of biological pest control resources, the researchers have developed a product that is currently undergoing tests in the field.

Eine Frau auf einem Markt in Kenia verkauft ihre Tomaten.
Poisonous or not? In Kenya, tomatoes are usually produced with the help of large quantities of pesticide.

From laboratory to field

The development of solutions in the laboratory and in the field is just the first step, however. If farmers are to put an end to the excessive use of toxins and help achieve a breakthrough for an integrated form of pest control, they need to be educated about all the different aspects of each method: “How would I recognise the presence of the various pests, and at what stage should I take countermeasures, and what measures should I use? What are the effects of using synthetic pesticides on the people who work in the fields? What are the effects on the product itself (the tomatoes)?”

Dr Samira Mohammed and her team are determined to convince the Minister of Agriculture and (especially) the farmers themselves of the results demonstrated by their research: that it is possible to produce healthy tomatoes, for the benefit of everybody involved – the producers, the consumers and the environment.

Tuta Absoluta: A moth destroys the tomato harvest.


Agriculture, Knowledge

The tomato leaf miner – a nightmare in Kenya and Switzerland

The tomato leaf miner moth “Tuta absoluta”, which originates from South America, became a nightmare for tomato producers worldwide within a few years. Luckily today, there are effective organic methods of pest control, as a visit to the tomato canton “Geneva” in Switzerland shows.