JOHANNESBURG – Scientists have called for urgent action to stop the spread of caterpillars that were first thought to be armyworms from decimating maize crops across Africa.
The caterpillar poses a major threat to food security and agricultural trade, warns the Centre for Agriculture and Biosciences International (Cabi).
Last week Liberia’s President declared a state of emergency and appealed for international aid to fight a plague of caterpillars that is spreading across Liberia, destroying whole farms within days and contaminating water sources with their faeces.
Liberia is in the middle of its worst infestation of crop-destroying caterpillars since the 1970s.
Both Liberia and neighbouring Guinea, which has also been affected, have been carrying out aerial spraying against the insects - and Sierra Leone, which is also at risk, has mobilised chemicals and personnel to its border with Liberia
At first the insects were thought to be armyworms but it soon became clear that this wasn’t the case due to differences in crops that were targeted, the positioning of cocoons and an unusual looping behaviour.
After a recent field investigation, the UN’s Food and Agriculture Organisation (FAO) was unable to identify the species and sent it to CABI and the International Institute of Tropical Agriculture (IITA) in Nigeria who confirmed that the species was Achaea catocaloides, a pest endemic to West Africa.
“Correct taxonomic identification of this insect is crucial for managing this worrying problem,” said Eric Boa, head of the Global Plant Clinic (GPC) at CABI.
“The wrong control programme can waste millions of dollars and cause new problems. Now efforts can be focused in the right direction.”
The invasion began in Bong County before spreading into neighbouring Lofa and Gbarpolu counties. To make matters worse, the worms are now spreading to neighbouring Guinea and towards Sierra Leone.
“The farmers in Liberia know these caterpillars but they have never seen them on this scale. It is extraordinary what has been seen here,” said Dr Winfred Hammond, an FAO entomologist, based in Accra, Ghana.
One piece of good news for farmers is that the caterpillars are likely to be easier to control than armyworms because they spin their cocoons on the ground under fallen leaves rather than underground.
Trampling or fire may be a control option, however with such extensive outbreaks spraying with pesticides is likely to have the most success.
These pesticide options are too expensive for most farmers, so the government is stepping in and calling for international assistance to begin aerial crop spraying.
It will be particularly challenging to reach the sites of the caterpillar eggs which are laid on the leaves of very tall Dahoma trees.
The cause of this year’s unexpectedly large outbreak is likely to be unusual weather patterns, including a particularly long rainy season last year, according to Dr Kenneth Wilson, an ecologist from Lancaster University.
The next stage is to step up a programme of pesticide spraying which until now has failed to reach any more than a dozen of more than 100 affected villages, according to Hammond.
“We cannot avoid applying pesticides. Now that we have an accurate identification, we can choose a pesticide which is specific to this species of caterpillar,” said Hammond.
“But in the long term, we have to take this as an opportunity to develop early warning strategies for countries in West Africa. Not only for these caterpillars, but for other migratory pests.”
National forecasting systems exist in some African countries to warn farmers about possible outbreaks during the growing season so that they have time to spray crops, if they can afford to.
However, these measures don’t always work because the attacks can be very localised and often affect isolated communities that are difficult to contact.
