It seems like the continent of Africa just can't catch a break. The Liberian President Ellen Johnson-Sirleaf has declared a state of emergency in response to a plague of crop-destroying armyworms. The bugs are among the world's most destructive agricultural pests. Liberia isn't the only country faced with this mounting problem. Farmers in Kenya and Tanzania have also suffered outbreaks in recent years. Something drastic needs to be done and quickly. The last time Liberia was attacked on such a large scale was in the late 1970s. The losses this time around could cause serious food shortages. The country is already heavily dependent on imported rice to feed its 3.5 million citizens. The government says it cannot cope with the scale of the outbreak and has called in the UN Food and Agriculture Organization (FAO) to help. To make matters worse, the worms are now spreading to neighbouring Guinea and towards Sierra Leone. The best weapon that can be used against the pest is to spray crops with chemical insecticides.
What exactly are armyworms?
The menace known as the "African armyworm" is in fact a caterpillar. During the rainy season, the insects emerge in sudden swarms and rapidly devour crops such as maize, sorghum, millet, rice and sugar cane. The pest gets its name from its habit of "marching" in large numbers into crop fields. Like locusts, armyworms appear in huge numbers, ravage farms, and then move on once fields are barren. They also cause disease, as their faeces enters rivers and streams can contaminate drinking water supplies.
Where did they come from?
The armyworms are the larvae of nocturnal moths, of the species Spodoptera exempta. During the rainy seasons, the moths spread and begin laying eggs in grasses and food crops. Each female lays between 500 and 1,000 eggs in her 10-day lifetime. The moths are capable of long-distance migration - more than 100km (60 miles) per night - allowing the swarms to spread rapidly.
Once hatched, the larvae migrate through grasslands in snake-like colonies. On reaching crop fields, they begin feasting. At full size (5cm - 2in) the caterpillars can lay waste to whole farms within days. They then simply move on to the next available target. Source: BBC News UK
A more radical approach to prevention of the spread of armyworms is a virus known as NPV, which is being investigated by researchers from the UK, Canada and Tanzania. According to BBC News, the naturally occurring virus is specifically lethal to army worms, but it appears too late in most years to prevent them causing serious crop damage. Scientists hope to study and harness the virus, to create an effective pest control technique. The last thing Africa needs is another country in the throes of massive food shortage.
It seems like the continent of Africa just can't catch a break. The Liberian President Ellen Johnson-Sirleaf has declared a state of emergency in response to a plague of crop-destroying armyworms. The bugs are among the world's most destructive agricultural pests. Liberia isn't the only country faced with this mounting problem. Farmers in Kenya and Tanzania have also suffered outbreaks in recent years. Something drastic needs to be done and quickly. The last time Liberia was attacked on such a large scale was in the late 1970s. The losses this time around could cause serious food shortages. The country is already heavily dependent on imported rice to feed its 3.5 million citizens. The government says it cannot cope with the scale of the outbreak and has called in the UN Food and Agriculture Organization (FAO) to help. To make matters worse, the worms are now spreading to neighbouring Guinea and towards Sierra Leone. The best weapon that can be used against the pest is to spray crops with chemical insecticides. 
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