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Turning the Worm - Tanzania
Plagues of African armyworm erupt in Tanzania with the start of each rainy season. These voracious caterpillars, larvae of the Spodoptera exempta moth, multiply rapidly to such large numbers that both cereal crops and pastures are devastated. A novel biological control technique using basic equipment has been devised to combat this threat.
African Armyworm
African armyworm are the larvae of the night-flying migrant moth, Spodoptera exempta, and appear between December and May. The life cycle is generally around 30 days – see Figure 1.
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Figure 1: Life cycle of the African Armyworm.
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Metamorphosis
is the process of change that insects go through in their life cycle from egg to adult. As the larvae, which in the case of moths and butterflies are also known as caterpillars, grow they cast off their skins in a process called instar. Armyworm caterpillars appear at the 5 th instar.
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The white eggs are laid in clusters on the leaves of food sources such as maize or grass. Depending on the temperature they hatch in two to five days. In the early stages the small caterpillars are green and often inconspicuous. As they develop they can grow up to 30 mm long and have dark stripes that make them appear black. Armyworm caterpillars are most dangerous in the gregarious form when they gather together in outbreaks of up to 1000 per square metre. These caterpillars crowd together to feed and march on to new food sources, consuming all food in their path – hence their
name of armyworm.
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| Tan armyworms. Credit: Wilfred Mushobozi, PCS |
Overall losses of 30 per cent for crops have been estimated, but in major outbreak years losses of up to 92 per cent in maize have been recorded. Outbreaks begin in Tanzania and are serious in 9 out of 10 years; in 2001 they covered 157,000 hectares of crops and pasture. In major outbreak years the pest subsequently migrates to produce further extensive outbreaks in Kenya, Uganda, Ethiopia, Somalia, Mozambique, Zambia, Eritrea and may travel as far as Yemen. The armyworm is also widespread in North America.
War Against the Armyworm
Previously the only form of control against the armyworm was to use expensive and environmentally damaging insecticides. However, the armyworm is now providing the means of its own destruction. A new solution to this problem is being developed by scientists in the UK and Tanzania with the assistance of local farmers. This uses a naturally occurring insect virus, called NPV (nucleopolyhedrovirus) that can kill up to 98 per cent of armyworm caterpillars. The virus used is naturally present in East Africa and specific to African armyworm, so is completely safe for humans, other animals and even other insects.
The main problem with NPV is that it spreads too slowly to stop plagues, and generally it arrives too late to stop the damage. However, NPV can be sprayed like other chemicals, and once sprayed the virus spreads and multiplies in the armyworm, so it is a good option for control over a wide area for a mobile insect like the armyworm, as it does not bring the harmful side-effects of chemicals. A worldwide collaboration, with a consortium of scientists from the UK (funded by the DFID Crop Protection Programme), CABI Africa Centre, USAID with links to EMBRAPA in Brazil, together with Tanzanian researchers, have developed a system to mass produce NPV cheaply. NPVs are robust organisms and amenable to mass production, provided quality control issues are adequately addressed. Dead moths from armyworm that have been infected by the virus are harvested, ground up and processed to produce a cheap but stable biological insecticide. Using this process the cost of producing NPV in Tanzania is much less than the previously used chemical insecticides which were imported.
To be effective NPV has to be sprayed on to the caterpillars early in their life cycle, so it is vital that information about outbreaks is gathered quickly. A community-based armyworm forecasting pack has been developed with villagers for their use and is now being promoted more widely. The pack has been distributed as an integral part of a training course for farmers and extension agents. One of the project collaborators, Dr Roger Day of CAB International (Africa) based in Nairobi, assembled and published the packs on behalf of the Armyworm Forecatsing project funded by DFID through NRInternational.
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| Farmers talking about armyworm. Credit: Roger Day, CAB International |
The pack comprises a pheromone trap, rain gauge, guidance notes and stationery for recording data. In parts of Tanzania, farmers have been trained to develop a weekly forecast:
· Look at vegetation to find armyworms.
· Set pheromone traps to enable the counting of moths. These pheromone traps attract the armyworm male moths using the artificial scent of mating armyworm females. The reports provide projects of caterpillar outbreaks two weeks hence.
· Read rainfall data, as infestations generally arise when the rains are good.
Communication
This information needs to be communicated to the wider community for effective action to be taken. In the past this has been difficult because of the complex hierarchical communication channels. However, recent work with various stakeholder groups has sought to identify ways to improve this system. The Government of Tanzania has supported research into the traditional roles within communities, looking to develop local forecasting tools and process that will then feed into more centralised communication centres, which in turn pass this data back to farmers and pest management organisations.
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Poster warning the Kimashuku villagers in Tanzania that there is a high probability of an armyworm outbreak and they should prepare to protect their crops.
Credit: Frances Kimmins, n r international
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More widespread cooperation is also being developed by the Southern African Development Community (SADC). They have established the Information Core for Southern African Migrant Pests (ICOSAMP). This is a regional network of information officers who submit monthly reports on the status of migrant pests, including armyworm, in their country to the ICOSAMP co-ordinator. They then produce monthly maps of pest infestations and disseminate this information through bulletins and on their website at http://icosamp.ecoport.org/.
Results and Further Research
Although these research initiatives are still in the trial stage the results so far have been impressive, with a 95 per cent kill. The project has alerted farmers to the armyworm threat and this knowledge is spreading throughout the communities. The government is supporting this work by providing sprayers and protective overalls to farmers to enable them to respond to outbreaks. It is hoped to extend this work to include about 15,000 small-scale farmers.
Other research is looking for solutions using local materials, such as botanical insecticides from neem. The Neem tree (Azadirachta indica) is a shade tree widely grown in Africa. From its berries and leaves simple water based insecticidal extracts can be made for pest control. Some 50-80% of farmers in armyworm outbreak areas have neem trees and their leaves and / or berries could be used to protect cereal crops from armyworm by smallholder farmers.
Trials carried out in Tanzania showed that both neem seed and leaf extracts show some promise as control agents for armyworm though they act more slowly than insecticide and do not have the longer lasting effect of NPV. While locally available neem was effective the evidence is that this varies very significantly according to tree provenance, season and growing conditions so expanding its use requires caution. However its widespread availability in some key outbreak districts such as Dodoma, makes its use a potential option to poorer farmers. Outbreaks generally occur in Tanzania before neem sets seed so that the leaf extracts are most practical form of neem for armyworm control. The high bulk of neem needed and transport costs means it is not feasible to recommend its use on a large scale, but it may have a role for subsistence farmers who lack the resources to buy pesticide. The use of local neem is already being promoted in some target districts of Tanzania by the Government Pest Control Services and its effectiveness is being monitored.
Acknowledgements
This summary is an output from Crop Protection programme research projects funded by the UK Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of DFID.
Further Information
Participating Organisations
Natural Resources Institute
University of Greenwich
Chatham Maritime
Kent ME4 4TB
UK
Website: www.nri.org
Contact: David Gzywacz, Project Leader
Email: D.Grzywacz@greenwich.ac.uk
Pest Control Services
Ministry of Agriculture
PO Box 7433
Arusha
Tanzania
Contact: Wilfred Mushobozi
CABI ARC
PO Box 633-00621
Nairobi
Kenya
ICOSAMP
c/o Dr M Kieser
Agricultural Research Council - Plant Protection Research Institute
Private Bag X134
Queenswood 0001
Pretoria
Republic of South Africa
E-mail: KieserM@arc.agric.za
Contacts
Dr F Kimmins
DFID Crop Protection Programme
NR international
Bradbourne House
Aylesford
Kent ME 20 6SN
UK
Website: http://www.cpp.uk.com/
References
Smith S. The Laboratory Culture of the African Armyworm, Spodoptera Exempta. Natural Resources Institute (NRI) 1998
Grzywacz D. and Mushobozi W. (2004) ‘A local solution to African Armyworm’ Biocontrol News and Information March 25, (1), 7-8N.
Grzywacz D. (2004) 'Novel technologies for the control of
armyworm Spodoptera exempta. on smallholder cereals
developed evaluated and promoted.' Final Technical Report
of DFID Crop Protection Programme project R7954 . NR
International, Alyesford UK.
Anon (2004). ‘Biological weapon used against armyworm’. Appropriate Technology, Vol. 31, No. 1, pp 60-61.
Rose D.J.W., Dewhurst C.F., Page W.W. The African Armyworm Handbook: The status, biology, ecology, epidemiology and management of Spodoptera exempta (Lepidotera: Noctuidae ) Natural Resources Institute (NRI) 2000
Other Relevant Hands On Case Studies
Green Muscle – Benin
http://www.tve.org/ho/doc.cfm?aid=995
The Bug Business – The Netherlands
http://www.tve.org/ho/doc.cfm?aid=392
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