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Insect specialists have identified the caterpillar species that is ravaging crops in more than 100 Liberian villages — and have found it is more benign than was thought.

Millions of caterpillars have been destroying coffee, cocoa, plantain and banana crops, and contaminating water supplies with their droppings in Bong County, northern Liberia, for the past three weeks.

They were first thought to be the destructive army worms of the moth Spodoptera exempta but, after their behaviour was seen to be different, Georg Goergen — an entomologist at International Institute for Tropical Agriculture in Benin — identified them as the tree-dwelling caterpillars of another moth, Achae catocaloides rena, from digital photographs.

Goergen said that the caterpillar's presence on crops in Liberia is something of a mystery. "Achae catocaloides rena are forest species generally found on trees. How they got to land on crops still needs to be found out," he told SciDev.Net.

But the identification could make it easier to remedy the situation. Goergen said that while army worms deposit their eggs underground — making them difficult to reach with pesticides — these caterpillars lay cocoons on the ground.

The authorities now need to find a pesticide that will kill the caterpillars without affecting the crops or contaminating precious water supplies. The news agency Reuters has reported that spraying teams have already started applying pesticide.

Goergen said that colder-than-average temperatures at the start of the year followed by warming could have caused the outbreak, as tree caterpillars react strongly to temperature fluctuations.

He added that the loss of forest habitat in the area could also have encouraged the caterpillars to seek food elsewhere.

He called for an observatory system to be established to track the evolution of the insects, as army worm moths can fly for up to 1,000 kilometres. "Once the insect number has exploded, it's already too late," he told SciDev.Net.

The caterpillars also appear sporadically in Benin, where they appear to hibernate seasonally, leading Goergen to predict that the caterpillars will reduce in number dramatically by March.

The tree caterpillar is also attacking border villages in Guinea, and cocoa plantations in the Ivory Coast are on the alert.

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