Intro: For the farmers of the GADC, cotton is a cash crop, a crop with which they can earn money, and which is replaced the following year by other crops such as maize, cabbage, pumpkin, sesame or chillies according to the crop rotation system. No pesticides are used in organic farming. This makes it important for farmers to know methods of keeping pests at bay using biological means – e.g. beneficial insects – and thus protecting the harvest. Existing and traditional knowledge in this regard must be preserved and passed on. Research in this field is just as important. The award-winning journalist Bettina Rühl visited ICIPE, the ‘International Centre for Insect Physiology and Ecology’ in Nairobi, the Kenyan capital in neighbouring Uganda, and describes their work in the field of biological pest control in the following article. By Stefan Rennicke
From the autumn armyworm to rice moths – the list of insects that destroy many tonnes of crop in African countries every year is long. In Nairobi, scientists are researching biological ways to put a stop to the insects.
By Bettina Rühl
Sevgan Subramanian looks intently into the glass cage. ‘See, there?’ asks the Kenyan scientist, ’it almost looks like a black speck of dust. But it’s a female parasitoid that is laying eggs in the eggs of the autumn armyworm’. The entomologist laughs quietly, perhaps amused by the way one species is eliminating another. ‘Outwitted’, one would probably say, if they were living creatures with consciousness. Subramanian heads the Environment Health Theme at ICIPE, the renowned International Centre for Insect Physiology and Ecology in the Kenyan capital Nairobi.
Subramanian has made a name for himself as a scientist because, among other things, he and his team have discovered methods for ecologically controlling the autumn armyworm – a maize pest that originally comes from the Americas. It has been spreading worldwide for several years, including in African countries since 2016. With catastrophic crop losses for farmers. According to figures from the UN Food and Agriculture Organization (FAO), the voracious larvae destroy up to 50 percent of the harvest once they have infested a field.
This is a dramatic amount, as most farmers in the East African country produce mainly for their own needs, and maize is the most important staple food in Kenya. What the pest eats is immediately missing from the farmers’ own plates – and not just in Kenya. According to the FAO, the autumn armyworm causes up to 18 million tonnes of maize crop losses in sub-Saharan Africa every year. Over 300 million people are affected by the consequences, i.e. hunger and poverty.
In Subramanian’s laboratories, glass cages stand next to and on top of each other. Large holes at the front are closed with gauze, the ends of which are knotted. The researchers can reach in without the insects being able to hatch out. The cages contain eggs or larvae of the autumn armyworm, along with various species of their natural enemies. ‘We want to know which of these enemies are particularly effective in which climate zones,’ explains Subramanian.
Anyone who listens to him can regain confidence that people are not at the mercy of the autumn armyworm and other pests, even if they do not use expensive chemical pesticides – which are unaffordable for most small farmers. There are other reasons why Subramanian does not believe in using chemicals to combat the unwanted creatures: ‘We destroy the natural enemies of the pests every time,’ he criticises. ‘Apart from possible chemical residues on the food and possible health consequences.’
Instead, the researchers at ICIPE are focusing on biological methods. Two years ago, they achieved a breakthrough in controlling the autumn armyworm: they found three native species of parasitic wasps that destroy the offspring of the voracious pest. In a field trial, they released hundreds of thousands of these parasitic wasps with autumn armyworm infestations into Kenyan maize farms. The released species could decimate the pests by up to 55 percent.
The biggest problem is pests that appear somewhere new, explains Subramanian. This is occurring more and more frequently as a result of climate change: Climate zones are changing and insects are suddenly finding ecological niches in regions that were previously uninhabitable for them – like the tiger mosquitoes in Europe recently. ‘The invaders initially have no natural enemies there at all,’ the scientist explains. ‘After a few years, this will stabilize, however until then, the new pests have free rein.’ Like the autumn armyworm in African countries. The researchers at ICIPE see their task as accelerating the natural process by carrying their enemies after the pests, so to speak.
Other methods are even simpler, including push-pull cultivation, which was developed by ICIPE. Legumes are planted between the maize plants, which repel the autumn armyworm and other pests with their odour. Napier grass is planted around the field, which attracts the insects. According to one study, fields infested with the pest but managed using the push-pull method suffered around 80 per cent less damage than fields managed normally. It is clear to Subramanian that he is pleased with such successes. And above all, you can sense that he is fascinated by how living organisms control each other under favourable conditions.
Bettina Rühl is a freelance journalist specializing in Africa. She has lived in the Kenyan capital Nairobi since April 2011. Her features and reports appear in various ARD radio programmes, magazines and newspapers. She has received numerous awards for her reporting from and about Africa and was honoured with the Order of Merit of the Federal Republic of Germany in 2020. Bettina Rühl is chairwoman of the correspondent network weltreporter.net.
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Photos © Bettina Rühl, Stefan Rennicke