Issue 182


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Creative Pest Control, RH #182
By Florianne Koechlin

The following report comes from Florianne Koechlin, of Basel, Switzerland, who spent a week in Kenya observing the innovative approaches of the International Centre of Insect Physiology and Ecology (ICIPE)towards some of Africa's key problems in agriculture.

The ICIPE specializes in biological pest control, using modern science to search for cheap and sustainable solutions to control stemborers, tsetse-flies, locust-swarms, ticks, fruitflies, anopheles-flies (vectors of malaria) etc. Their collaboration with and capacity-building of farmers is essential.

Stemborers and the Push-Pull System

At a field station of ICIPE near Lake Victoria, the small maize (corn) field in front of us looks dreadful: the plants are only 1 m high, the leaves yellow and full of holes, and there are almost no cobs at all. Close by, Mrs Ouzo, the farmer of these fields, shows us another maize field: the plants are over 2 m high, with dark green leaves and healthy cobs. It's the same maize variety on both fields, planted on exactly the same day. The difference could not be bigger.

The first maize field was destroyed by stem-borers and striga (witchweed), the two most important pests of maize and sorghum in all Africa. Stemborers [referred to in Canada as cornborers, the pest transgenic Bt corn is supposed to deal with] can destroy up to 80% of the crop in no time, the loss of crops due to striga varies from 20 to 80%. If both pests are present at the same time, they can easily destroy the whole crop. Around the second field, Mrs Ouzo had planted 3 rows of napier-grass. "The beauty of this grass is that its odours are attractive to stemborers", says scientist Zeyaur R. Khan. [Remember, corn/maize is a grass.] "The grass then produces a gummy substance that traps the pests. Only about 10% of the stemborer-larvae survive in the end". Between the maize rows, Mrs Ouzo planted desmodium, an earth-covering plant whose odour repels stemborers. She was chosen as one of the first farmers for the project because her fields were most heavily infested by stemborers and striga.

The stemborer is attracted to napier-grass (Pennisetum purpureum) at the outside of the field and repelled by desmodium (Desmodium uncinatum) from the inside of the field. This "push-pull" system was originally developped by ICIPE, starting with the knowledge that stemborers must have been indigenous to East Africa long before maize was introduced there (about 100 years ago). Originally, its host must have been different kinds of wild grass and only later on did it specialize in maize, which had no resistance against it and was more nutritious. For 4 years, Khan and his team selected several species of wild grass with strong stemborer-attracting odours and cultivated them in a garden near the local station. Farmers from the surroundings were invited to choose from the different varieties: they mostly preferred Napier- and Sudan-grass, which both look very similar to maize and are good fodder. Varieties of wild grass looking more like "weed" were passed over.

The selection of "repellent-plants" was successful, too: molasses-grass (Melinis minutiflora) reduced the loss of crop from 40% to 4-6%. . . The silver-leafed desmodium is a good stemborer-repellent, with the added advantage of being a soil-enriching, nitrogen-fixing legume that keeps the soil moist and protects it from erosion. But best of all, desmodium is most effective against Striga, to everybody's surprise. With desmodium, striga is suppressed by a factor of 40 compared to maize monocrop. Although striga is a very beautiful weed with its pink blossoms, it is a deadly plant, being a parasite on maize roots, to say nothing of the fact that a single plant produces 20,000 tiny seeds that disperse easily. In all Africa, problems caused by Striga are increasing. . .

"Last year, I sold my napiergrass and desmodium as fodder for 6000 shillings [about $100]. With this money, I could afford to pay the school fees for my kids. This year, I am planning to produce desmodium seed as well because all of my neighbours want to go for this push-pull system. Maybe I can afford a cow then", says Mrs Ouzo. ICIPE plans to establish the push-pull system not only in further areas in Kenya, but also in Ethiopia, Uganda and Tanzania, in close co-operation with the national programmes.

Stemborers and a small wasp

Stemborers have natural enemies which can be used as well: five different species of stemborers exist in Africa. The most aggressive one is the spotted stemborer (Chilo partellus) which was introduced from India/Pakistan to Africa some 70 years ago, so ICIPE scientists went to India to do research in these centers of origin. They found Chilo partellus being a harmless pest kept well under control by several natural enemies. One of them is the little wasp Cotesia Flavipes Cameron: it tracks down the stemborer larvae deep inside the stem and lays its eggs into the pest; these then hatch out and consume the borer from within. After careful testing, this wasp was released on 3 sites in Kenya. By now, the wasps are well established; they not only go for Chilo partellus, but for 3 other stemborer varieties, as well. The latest results show that stemborer infestation could be reduced by 53% in these areas. "Maize only came to East Africa some 100 years ago, and had no resistance against the stemborer. The immigrated stemborer Chilo partellus had no enemies. Any ecological balance that existed between native stemborer and wild grasses was severely disturbed. We try to reintroduce a natural equilibrium into this system", says Bill Overholt.

I wanted to know if Cotesia flavipes could not harm other insects as well. Overholt responded, "The host range of this wasp is limited by its searching behaviour, which restricts its hosts to stemborer larvae found tunnelling inside the stems of larger grasses. And then only certain stemborers, and only the later larvae instars of these, are suitable for the development of the wasp-parasites. We made careful evaluations, and we did not find one other insect matching all these requirements."

ICIPE is working closely together with national programmes in Kenya, as well as in Uganda, Somalia, Mozambique, Malawi, Ethiopia, Zambia, Zimbabwe and Zanzibar to release the wasp Cotesia in all of these countries.

Stemborers and transgenic Bt-maize from Novartis

A third--and very different--strategy to fight the stemborer consists in introducing genetically engineered Bt-maize. The African stemborer species are close relatives to the European corn-borer, against which the Bt-maize was constructed. The Swiss company Novartis wants to test and introduce Bt-maize in Kenya: in spring 2000, they started a 5-year program with Bt-maize, at a cost of $6.2 million, in co-operation with the Kenyan Research Institute KARE and the Latin-American CYMMIT.

This project was presented at a meeting in March in Nairobi, "which turned into a tribunal against Hans Herren, the director of the ICIPE. They accused him of being an ennemy of Africa, and of assuming Africans were incapable of handling biotechnology" (The Tages-Anzeiger, 21/6/00). Klaus Leisinger, director of the Novartis Foundation for Sustainable Development, accused Herren of having gone to the Swiss development agency to get them off GMOs. This is not true. Hans Herren is critical, but he is not a strict enemy of genetic engineering, and all he did was tell an audience of Swiss government officials about his fears: "Possibly, transgenic maize will be part of the solution in the far future. But what about the other problems? The interesting thing about the push-pull-system is that it already exists and the farmers use it. It was developed together with the farmers. With the push-pull method, we have an integrated solution for the problems of the stemborer and striga. We have protein-rich fodder, nitrogen fertilizer and a good protection against soil erosion. All this within one field. It's a system that's enhancing justice and a sustainable agriculture."

ICIPE: integrated research on tropical insects

350 people work at the ICIPE, mostly Africans. The main issues for ICIPE are Africa's most damaging pests, at costs of millions of lives (humans and animals) each year and 30% crop losses on average: the Anopheles mosquito (vector for malaria), the tsetse-fly (vector for human sleeping sickness and several fatal animal diseases, such as nagana in cattle and sura in camels), the tick, the locust, the fruit-fly (which destroys 20-80% of the mango crop each year)--and the stemborer. Useful insects are studied as well: ICIPE initiated local silk production with African silkworms and local honey production. Another main issue at the ICIPE is capacity building (from farmers to PhDs).

Interdisciplinary teams of scientists are doing pioneering work in the area of biological pest-control. They are working on insect behaviour and population ecology, they study the ways insects communicate, they analyze the odours of insects and plants, and search for the molecular conditions of vector mechanisms, they do molecular insect taxonomy and search for ways to protect--and use--the vast biodiversity. All the time, the goal is to use modern science to develop simple and efficient methods that farmers can afford. "We are looking for solutions in nature, we want to understand the system and identify the weak links, where we can intervene. How can we favour natural enemies of the pests, what odours will attract or repel them, how can we reintroduce a better equilibrium?", says director Hans Herren. Francois Omlin, a scientist who started to work at the ICIPE recently, confirms: "I do not know of any other research institute worldwide working in this area in a comparable interdisciplinary way--in this place, molecular biologists are working together with behavioural scientists and entomologists. And furthermore, all of us are in close contact with the farmers."

"Biological pest-control is not as sexy"

Hans Herren won the World Food prize in 1995 because he and his team achieved control over the cassava mealy bug that was endangering the staple crop cassava in large areas of Africa (from Senegal to Mozambique) and threatening some 300 million people. They gained control over the bug with the help of a small wasp--without chemistry, and without any extra costs for the farmers. Thoughtfully, Hans Herren says: "Today, I probably would not get the money for such a big programme. Today, all funds go into biotechnology and genetic engineering. The genetic people would try to construct a cassava that is resistant against the mealy-bug. Biological pest-control, as we do it here at the ICIPE, is not as spectacular, not as sexy. I see a big problem here."

Scents against locust-swarms

In the world of insects, scents play a major role not only as a means of orientation (attracting and repelling 'road signs'). For insects, odours are the most important means of communication. Take, for example, desert locusts. For 10 years, Ahmed Hassanali and his team at the ICIPE have done research on the desert locusts, or more strictly speaking, on their communication. The central question was: how and why do harmless single locusts suddenly turn into most dangerous swarm locusts? What are the mechanisms of 'gregarisation' and the development of locust outbreaks? In general, desert locusts are solitary insects. Over several generations, at particular times, they build small swarms. Sometimes, they form bigger swarms, which can, all of a sudden, turn into one huge swarm of as much as 40 billion insects. In Madagascar, in the years 1997/98, a swarm like this destroyed the vegetation in an area of 1.4 million ha. For ICIPE scientists, odours were the key to understanding swarm formation. Hassanili and his group isolated and identified 5 different sets of chemical messages. These 'morse-codes' regulate behaviour and life-style of desert-locusts. Some odours regulate the behaviour in swarms of young and of adult insects, others determine their behaviour of cohesion, the synchronous maturation, and the communal oviposition. Another volatile chemical attracts the females to their common egg-laying place.

At this point, the scientists intend to intervene: they exposed young hopper-gangs to a very low concentration of odours from adult locusts. The results were most fascinating: the hoppers became hyperactive; they lost their orientation and began to cannibalise. The hopper-swarm--shortly before a huge mega-organism --fragmented into separate parts. The swarm insects turned into solitary insects again, becoming an easy prey for birds. Electrophysiological studies at the University of Lund (Sweden) showed that the odours of adult insects blocked the signal-transfer between the hoppers, resulting in a total loss of communication between the individuals. "As if you cut the telephone line", says Ahmed Hassanili. The moment communication breaks down, nothing happens anymore. The swarm is held together only by intense and constant communication between the insects. The ICIPE now produces the volatile chemical in larger quantities and hopes to test this method during the next outbreak. "This would be a very simple und extremely environmental-friendly method", says Hassanili. "During the last big plague $250 million were used exclusively for insecticides, $12 per ha. We estimate that with the odour-method costs will be at one dollar per ha at the utmost. And all this, without spraying toxic insecticides and without longtime accumulation problems. -- Blauen Institut, 6/00 -www.blauen-institut.ch


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