快猫短视频

INDIA鈥橲 Green Revolution may have a deadly sting in its tail. The extensive
use of inorganic fertilisers in paddy fields is fuelling mosquito-borne
epidemics of Japanese encephalitis, according to Indian researchers. Using
environmentally friendly organic fertilisers like blue-green algae could control
such epidemics, they say.

鈥淚f the association is strong enough it would contribute to a change away
from inorganic fertilisers,鈥� says Martin Birley of the Liverpool School of
Tropical Medicine.

Japanese encephalitis is a viral disease transmitted by mosquito bites. It
infects nearly 50,000 people in Asia alone every year, killing about 15,000
people worldwide while leaving half the survivors with permanent brain damage.
Before 1970, the disease was virtually unknown in India. 鈥淏ut since then we have
experienced large outbreaks of Japanese encephalitis,鈥� says entomologist John
Victor of the Institute of Vector Control and Zoonoses in Hosur.

This coincides with the soaring use of inorganic fertilisers in fields of
high-yield varieties of rice. In the state of Tamil Nadu alone, farmers used
791,000 tonnes of the chemicals in 1996-97 compared with just 296,000 tonnes in
1970-71.

鈥淢osquitoes that transmit Japanese encephalitis mainly breed in rice fields,鈥�
says Victor. So he and his colleague Rachael Reuben investigated whether the
large-scale use of fertilisers could influence mosquito populations. Using
60-square-metre plots, they compared the effect of nitrogenous inorganic
fertilisers and nitrogen-fixing blue-green algae bio-fertiliser on
mosquitoes during the rice-growing season.

They found that plots given the recommended dosage of 100 kilograms per
hectare of nitrogenous fertiliser had more than double the number of mosquito
larvae compared with plots sprayed with bio-fertilisers or with no fertiliser at
all. But rice production suffered when only organic fertilisers were used. 鈥淲e
cannot completely avoid nitrogenous fertilisers, because we need a better grain
yield also,鈥� says Victor.

So the researchers tested plots with a mixture of organic and inorganic
fertilisers. These plots had only 50 per cent more mosquito larvae than the
controls, but with better yields than before. 鈥淎gricultural scientists are now
promoting the use of blue-green algae in rice fields in India,鈥� says Victor. 鈥淲e
recommend it mixed with lesser amounts of nitrogenous fertilisers.鈥�

Some strains of blue-green algae are toxic to mosquito larvae in laboratory
conditions. These strains could be added to the fertiliser mix, says Victor,
although more work needs to be done to check whether they are effective in rice
fields.

But international funding for such research is lacking, says Birley, who鈥檚
also a member of a United Nations panel on environmental control of diseases
like Japanese encephalitis. 鈥淭he agencies that control research are not
enthusiastic about funding for environmental methods of mosquito control,鈥� he
says.