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Pests > Pests Entities > Insects > Moths & butterflies > Achaea > Spodoptera or Achaea outbreak West Africa

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February 2009. The BBC has reported an enormous invasion of armyworms in Liberia under the headingCaterpillars consuming leaves in Liberia. This can be found on its website ( The photo above is from the BBC website.

Farmers have heard of outbreaks of this kind many years ago, but never seen such damage. The caterpillars are attacking banana and cocoa. Some 400,000 people in 100 villages are affected, and the UN warns of a ‘second wave of infestation’. The mininstry of agriculture has done some spraying, but it seems it was too late. Even the insides of houses had to be sprayed.

A second report (, entitled Liberia faces a second wave, says that the presidernt of Liberia has declared a state of emmergency, Liberia and neighbouring Guinea have been carrying out aerial spraying,

The FAO reported that they had a crisis on their hands as the “moths can reproduce quickly, laying up to 1000 eggs within a week which grow into caterpillars within days…… With each female laying between 500 and 1,000 eggs, the caterpillars (of the genus Spodoptera) can devour an entire crop in a matter of days once they reach maturity. They grow up to 5cm (2in) in length.”

However, a member of Pestnet from Papua New Guinea questioned the identification given in the BBC reports. He said “(I) Don???t think this is a Spodoptera. The TV pictures looked like a semi-looper. S. exempta will not eat dicots (althought there was a report of them on young tea seedlings – not confirmed).”

The doubt was later confirmed on Pestnet when another member wrote:

“The insect outbreak in Liberia has been identified as Achaea catocaloides(Lepidoptera: Noctuidae).”

Editor: I made some comments on the episode at the time, and these can be seen below.

Comments and New Scinetis article

Could Pestnet help in Africa?

You may have read about the recent plague of caterpillars that munched its way across several African countries; a phenomenon as alarming as it was amazing. The consequences are simply dreadful, but would they have been as bad if PestNet had been there to give advice

The article below from the New Scientist is somewhat old, dated 20 January, and there have been updates since then. However, you can see from the first paragraph that there was some uncertainty about the species involved. Later, in an article I put out on Feb 2, the armyworm was said to be Spodoptera. Charles Dewhurst in Papua New Guinea questioned this, even without seeing a picture. Georg Goergen confirmed his suspicions, and Rangaswamy Muniappan told us it is not Spodoptera, but Achaea catocaloides.

As we know, pest management relies on correct identification of the problem; it is vitally important to get it right. And PestNet has already shown how identifications can be made correctly and quickly. Where there is doubt, taxonomists often call for specimens for critical examination, and make the identifications free of cost. Not only identifications are made on PestNet, but a lot of information on pest management is exchanged.

PestNet has been working in this way for nearly 10 years. Scientists help other scientists, extension workers and farmers. The collaboration, the generosity, the desire to help others is played out daily through emails, which now exceed 6000. During that time, PestNet has become firmly established in the Pacific, in Asia and the Caribbean. But attempts to set up a service for Africa, linked to the other regions, have so far not been successful.

One of the reasons for this is that the moderators do not know the countries of that continent, and getting partners is proving to be difficult, although we have found some. Communications are not as good as elsewhere, although they are fast improving with the rapid proliferation of mobile phones, now the primary means of communication throughout Africa. Funding opportunities to begin the service are few and far between. It all adds up to a service that has not happened.

What do members think we can do? There are members from Africa on the list: what do they think? If a service is needed, how can it begin? Can donors assist, or the international institutes?

I am convinced there is a vital need for PestNet. Let???s go back to where I began: if there had been members in countries with these caterpillar hordes, would the identification – Achaea, not Spodoptera – have been made earlier; and would management options have been discussed at the right time. Of course, we will never know. But surely it’s worth having a presence to deal with the many other similar events that will inevitably occur, both large and small?

Caterpillar plague strikes West Africa ??? from New Scientist

February 2009 by Debora MacKenzie

Update: On 29 January, the UN Food and Agriculture Organization confirmed that the caterpillars in the Liberia outbreak are of the same species of armyworm that is a well known pest in east Africa. However, the UN Food and Agricultural Organisation has now told New Scientist that their first impression, that they are an unidentified species with a strikingly different life cycle, has now been borne out by laboratory observations in Accra.

A THRONG of crop-eating caterpillars is threatening food supplies across west Africa, and could prove hard to control with pesticides. The crawling menace has appeared in northern Liberia, where hundreds of millions of the black larvae are devouring plants, fouling wells with their faeces and even driving farmers from fields.

They are now crossing into neighbouring Guinea, and the UN Food and Agriculture Organization (FAO) warns that in two to three weeks they will turn into moths that can fly hundreds of kilometres and could spread across west Africa, worsening food shortages in the region.

“The species is so far unknown,” FAO entomologist Winfred Hammond told New Scientist from Accra in Ghana, where Liberian specimens were being flown for analysis.

Several species of African caterpillars swarm over crops but unlike the best-known species, army worms, the newly discovered Liberian caterpillars reportedly climb trees to get away from hand-sprayed insecticides on the ground. Aerial spraying might kill them but the FAO fears this will contaminate water supplies.

Although too late to help farmers this year, a bio-pesticide already developed for army worms could be adapted for the new species. The idea would be to infect the caterpillars with a virus specific to that species, and then use mashed-up infected caterpillars against the rest. Such a pesticide could be made locally for a third of the cost of chemical sprays.

But there is a hitch: though UK agencies funded the pesticide’s development, commercialisation has stalled for lack of funds. “It has been “extremely difficult to get ??1.25 million for producing it locally,” says Ken Wilson of Lancaster University in the UK.