Scientists are making gloomy predictions that rising temperatures shall jeopardise not just human health but our crops as well
A STUDY conducted by British researchers concluded that with rising mercury levels, temperate farmlands face a
potential threat in the form of insecticide-resistant aphids (insects of the
Homopteran order, which live on plant
juices). The aphid population had till
date been kept under check due to winter frost, but when the average winter
temperatures rise, their population
receives a boost (New Scientist, Vol 148,
No 2009/2010).
The peach potato aphid (Myzus persicae) which reproduces asexually,
except when on a peach tree, is an agricultural pest feeding mainly on potatoes, oil-seed rape and sugar beet plants.
These pests feed on the sap of the plant
and spread viruses which can wipe out
entire fields. These pests had been controlled till date, but researchers now
claim that insecticide -resistant clones
have developed. These 'super-aphids',
are resistant to organophosphates,
carbamates and pyrethoid groups of
agricultural insecticides.
The defence mechanism of the
super-aphids is balanced by their
inability to survive in the cold. Stephen
Foster and his colleagues at the
Rothamstead Experimental Station in
Hertfordshire, UK, have conducted
experiments on insecticide - resistant
aphids to show that they are more likely
to die during a cold spell. Clones with
varying degrees of resistance were introduced into experimental plots of
oil-seed rape. It was found that the
most resistant aphids perished in severe
wintry conditions when temperatures
dipped below 2C.
These aphids use carboxylestrase E4
enzyme to break down the insecticides.
"The more resistant forms produce
more enzyme," explains Foster. This is
helped by the fact that they carry multiple copies of the genes which encode for
the enzyme. But this does not explain
the vulnerability of these 'super-aphids'
to the cold. The researchers assume that
since these duplicated genes appear on a
stretch of DNA which has moved from
one chromosome to another, they must
have done so by displacing other important genes. Experiments suggest that
these genetic changes interfere with
either the plant's warning signals indicating danger or the plant, due to other
changes, totally loses its ability to heed
these signals. The normal warning system comes in the form of chemical
changes in the leaf sap.
The greatest fear dogging British
researchers is that by the end of next
century, average winter temperatures in
Britain are likely to rise by 3C. With a
25 per cent reduction in the number of
frosty nights, the natural barrier against
the growth of super-aphid populations
shall tumble and crop destruction
would inevitably follow.
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