Science & Environment

Bats perform 'vital pest control' on crops

Corn earworm moth (Image: Josiah Maine) Image copyright J.Maine
Image caption The study recorded a 59% increase in corn earworm larvae in areas where bats were not present

Bats provide a service worth an estimated US $1bn (£649m) globally by controlling pests on corn crops, a study has suggested.

Scientists carried out a series of experiments to assess the economic and ecological importance of the nocturnal insect-eating mammals to farmers.

Globally, bat populations are under pressure as a result of habitat loss and the spread of diseases.

The findings appear in the Proceedings of the National Academy of Sciences.

"The results of this study are a testament to the value of ecosystem services," said co-author Josiah Maine from Southern Illinois University.

In North America, many bat populations are under threat from a disease called White-Nose Syndrome. Since 2007, the disease has killed millions of bats and continues to spread.

The US National Wildlife Health Centre estimated that bat populations in the north-east of the country have declined by about 80% since the first reported cases of bat fatalities as a result of the disease.

It added: "The true ecological consequences of large-scale population reductions currently underway among hibernating bats are unknown. However, farmers might feel the impact."

Mr Maine told BBC News that he was interested in finding out how effective bats were in terms of providing a pest control service to farmers growing corn (maize).

The team constructed a number of exclosures (a controlled, open-air experimental area) measuring 20 metres by 20 metres and seven metres high, consisting of netting that was suspended by cables.

"This netting allowed the insects to move freely but prevented bats from foraging in those areas," He explained.

"We were only interested in excluding the bats so we constructed the exclosures so all the netting could be slid to one end so we could open them up during the day to allow birds to forage in the area."

Using the data gathered from the field study and combining with other previously published data, the team was able to extrapolate the findings to a global scale and estimate a monetary value for the ecological service provided by bats in terms of pest control in cornfields.

The team wrote: "We estimate that the suppression of herbivory by insectivorous bats is worth more than US$1bn globally on this crop alone."

Mr Maine told BBC News: "Bear in mind that this figure does not take into account for the impacts of bats on the fungal diseases we found in the corn, or the micro-toxins produced by those fungal species.

"It also does not account for the reduced amount of pesticides used in fields, as bats could be providing an additional valuable service to agriculture by suppressing pest populations below the threshold where pesticides are necessary."

Farmers' friend

According to the IUCN's Bat Specialist Group (BSG), bat species account for one fifth of all terrestrial mammals.

As well as being an important predator of insects, bats are also considered to be key seed dispersers and pollinators for many plants.

Yet, the BSG observed: "They are among the most endangered of the world's creatures, primarily because much of their habitat has been eliminated by human development or because they are persecuted.

"Their loss has serious consequences for the ecosystems to which they belong."

An earlier study, publish in Science in April 2011, warned that the loss of bat species in North America could lead to agricultural losses in the region of US$3.7bn each year.

The authors observed: "Urgent efforts are needed to educate the public and policymakers about the ecological and economic importance of insectivorous bats and to provide practical conservation solutions."

Mr Maine echoed this view: "Bats are maligned in the media and there is a public fear, so if we can demonstrate a valuable, positive impact of bats then it is good for the species and it is good for society.

"What it suggests is that conservation is necessary not just from an ethical stance but from an economic standpoint as well."

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