Invasive species costing Africa $65 bn a year

Non-native species of weed, insect or worm can have catastrophic effects on farming, with just a single bug capable of reducing yields of staple crops across the continent.

Researchers based in Ghana, Kenya, Britain and Switzerland sought to estimate the annual economic hit caused by invasive species to African agriculture.

The team studied open source and peer-reviewed literature on species that were not native to the continent but had caused crop losses to assess the economic impact on yield, management and the cost of research.

Next, they surveyed more than 1,000 stakeholders -- including farmers, researchers and government officials -- about the financial implications of invasive species.

However, two fundamental errors in their method -- which passed through peer review unnoticed -- led them to correct the original study, published in May in the journal CABI Agriculture and Bioscience.

The team said Thursday it had mistakenly calculated the cost of weeding invasive plant species per kilometre, instead of per hectare.

This led to their original finding of $3.66 trillion lost annually due to invasive species in Africa being revised down several orders of magnitude to $65.58 billion.

Secondly, the original study said that an invasive moth species, Phthorimaea absoluta, caused an estimated loss of $11.4 billion annually.

But the team failed to correct their estimate to account for the abundance of the moths in individual countries.

In Thursday's correction they revised down the cost estimate to $4.1 billion annually.

"After publication, it was brought to our attention that the estimated cost of weeding was much higher than can reasonably be expected although the input data," the authors wrote in a correction notice.

"We apologise for the errors and any confusion they may have caused."