Caterpillar plague ruins Liberia’s most productive areas

An invasion of tens of millions of marching caterpillars prompted Liberia to declare a state of emergency last January. The Liberian government asked for international assistance after the plague affected around 500,000 people in over 100 villages.

While the reasons of the first outbreak are still unknown, experts agree that unpredictable weather patterns, an unusual rainy season and changes in agricultural activity may have contributed to worsening the plague. Scientists explain that insect numbers tend to remain low and largely unnoticed in West Africa, but when external changes occur there is always a risk that insects’ populations explode.

Caterpillars primarily live in the highest leaves of the Dahoma, a common West African tree. The caterpillars just fell down and began eating vegetation in the vicinity. The invasion is seen as Liberia’s worst outbreak in 30 years. The two-to-three cm long black and yellow caterpillars were devouring key agricultural crops such as coffee, banana and cocoa - all important sources of income for villages.

According to the Liberian representative for the United Nations’ Food and Agriculture Organisation (FAO), staple food crops such as maize, rice, sorghum and millet, which are scarce during this dry season, had generally not been affected.

The caterpillars were capable of destroying entire fields in very little time. As the moths which lay the caterpillar eggs travel exclusively by night, the spread of infestation was extremely difficult to monitor. Each moth is able to travel as much as 100 km a day, which raised alarm in neighbouring countries. The Ivory Coast, bordering Liberia, is the world’s top cocoa grower with almost 40% of global production and an important producer of coffee, rubber, palm oil and other crops.

The plague of the marching caterpillars has triggered serious health issues as the larvae polluted water systems and rural water sources. While the level of infestation lasted, farmers were unable to go to the land and work in the fields.

Insecticides sprayed by hand failed to reach the pests which climb into the canopy of trees up to 8 metres high. Aerial spraying wasn’t recommended as it could jeopardise water supplies.

A special team of crop protection specialists from the UN are now analysing all the options to find the best crop protection solution. Samples were collected for identification and digital photos send to internationally renowned laboratories such as the Commonwealth Agricultural Bureaux International (CABI) in the UK and the International Institute of Tropical Agriculture (IITA).

The caterpillar outbreak reveals the need to develop better response systems to protect against migrant pests. The Liberian Ministry of Agriculture is starting educational programmes with assistance from the United Nations so farmers are able to identify the pests. Liberia is planning on developing a Rapid Response Capacity programme so that the country will be better prepared for future invasions.