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EAST AFRICA: New Arsenal Against Armyworms

Isaiah Esipisu

Nairobi, Jun 3 2010 (IPS) - Farmers across Eastern and Southern Africa will soon have a new organic insecticide effective enough to kill one of their most deadly foes – the armyworm.

Scientists have developed a natural pesticide against the destructive armyworm. Credit: Cody Hough/Wiki Commons

Scientists have developed a natural pesticide against the destructive armyworm. Credit: Cody Hough/Wiki Commons

Armyworms or Spodoptera frugiperda, as they are known scientifically, are caterpillars that eventually develop into brownish-grey moths. If left unchecked they multiply into millions daily and have been known to clear the leaves off crops on hundreds of square kilometres of land in just a few days. Once the food has been exhausted in one area, they migrate to their next destination.

In January armyworms destroyed 35,000 hectares of crop, and threatened the food security of over 120,000 families in Malawi. In March, Uganda’s New Vision reported that an outbreak of armyworms destroyed almost 100 hectares of maize. And in previous years Sierra Leone and Tanzania have faced devastation due to invasions of armyworms.

The deadliest attack was in Liberia 2009, where armyworms attacked about 100 villages and damaged crops, including coffee plantations and pasture. Over 500,000 people were affected, and over 20,000 residents were forced to flee their homes.

But now scientists have offered farmers some hope.

Scientists have now developed a new organic insecticide that specifically targets armyworms, known as SpexNPV. The study of the development of SpexNPV has appeared in volume 27 of the scientific journal – ScienceDirect.


Previously, a non-chemical based pesticide made of a naturally-occurring terminal disease that affects armyworms known as Nuclear Polyhedrosis Virus (NPV), was used. But it killed all insects. This led scientists to develop SpexNPV.

The NP Virus was first discovered in 1965 in Tanzania, when armyworms were found succumbing to it.

“Dead insects were isolated for laboratory analysis. Since then, scientists have been working on it to find out the best strains that can attack only the armyworms without affecting other insects,” said Wilfred Mushobozi, the lead researcher during development of the biological pesticide, based at Eco Agri Consultancy Services, Tanzania.

To manufacture the virus, dead worms are crushed to release the virus, which is then mixed with water and sprayed over fields. Infected moths also assist in spreading the virus.

“Once in their hosts, viruses will always multiply through mutation. This is very advantageous to us because the insects are helping us manufacture the pesticide,” said Mushobozi.

But the SpexNPV does not work independently. Scientists have combined previous research on forecasting armyworm attacks with using the new organic pesticide.

“Forecasting is crucial for this pesticide to be effective because it doesn’t kill as fast as chemical-based insecticides. It makes the insects (first) fall sick, and then die later,” said Mushobozi.

Research was conducted in collaboration with the Natural Resources Institute (NRI) at the University of Greenwich; the Centre for Agriculture and Biosciences International (CABI); and the department of biological sciences at Lancaster University in the United Kingdom.

Mushombozi said after absorbing SpexNPV, the insects can still feed and reproduce, thus continuing to wreck havoc. “The earlier they are infected, the better, thus, the importance of forecasting,” he explained.

Community-based trials of armyworm forecasting began after the NRI developed a tool that lures male armyworms during the moth stage of their lifecycle.

“The tool, also known as a ‘pheromone trap’ is a plastic container containing rubber material that has been treated with pheromone bait from female (armyworm) moths,” said Dr. Hassan Nayem of the NRI.

A pheromone is a biological chemical secreted by female insects or even mammals that triggers the attraction of a male to a female. In the armyworm it is the basic indicator used by male moths to identify female moths for the sake of mating.

According to documented evidence, male armyworm moths are able to detect the scent of the pheromone from a radius of 10 kilometres, depending on wind direction.

“The pheromone trap also contains an insecticide. Once inside, the moths die, after which community forecasters count them every week,” said Nayem. “Killing them is important because once they are dead they cannot escape. This helps the forecaster count the exact number of (armyworm) moths trapped every week.”

More dead moths mean the likelihood of an attack, while lesser moths mean the opposite. According to scientists, more than 30 catches of the moths a week is a clear warning of a possible invasion of armyworms. When this happens, an alert is issued by word of mouth in schools, chiefs’ meetings, churches and community radio. Accordingly, communities spray the SpexNPV.

After successful forecasting trials, which began in 2001 and ended in early 2010, several communities in the Sub-Saharan African region have already benefited from free pheromone traps. Traps are being distributed by national organisations in Tanzania, Malawi and Zimbabwe in collaboration with CABI.

The research on SpexNPV has been completed and the product is being prepared for commercialisation. It is expected on the shelves once the due process of commercialisation is completed in various countries.

 
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