Insects introduced to curb the spread of water hyacinths are avoiding feeding on those weeds that have been contaminated by toxic metals
INSECTS that were introduced to
stem the spread of water hyacinth are
beginning to avoid feeding on the
weed because they are polluted by
toxic metals. However, the insects
seem to be developing resistance to
the toxicity by producing new cellular proteins and synthesizing new
ones.
In experiments conducted by scientists -at the.Indian Institute of
C210mical Technology in Hyderabad,
water hyacinth (Eichhornia
crassipes) plants were kept for a
week in solutions containing various
amounts of cadmium, zinc, mercury
sad manganese. The maximum
absorption of metals by the plants
a=arred in the first 24 hours, after
vMch the uptake was gradual.
The accumulation of metals was
Height in the roots, compared to
Other parts.
The plants absorbed metals with
No apparent deleterious effects.
However, when very high concentration of metals were absorbed, the
Leaves turned pale and plant growth was restricted.
When water hyacinth weevils
(Neochetina eichhornae) fed on the
plants they absorbed high quantities
of cadmium and zinc but low
amounts of mercury and manganese.
Adult weevils that fed on contaminated plants did noi show any toxic
symptoms - even when contamina-
tion was high - suggesting they were
able to develop mechanisms to resist
metal contamination. The insects
may have survived the toxicity by
physiological avoidance, but prolonged exposure to the metals could
result in genetic changes.
Studies showed the accumulation
of metals in insects led to the disappearance of some normal proteins
and the emergence of new ones.
Scientists are unsure of the changes
the new proteins,could cause but
they may be responsibIq for metal
detoxification by binding metal ions
and rendering them less.harmful.
The scientists found high accumulation of chromium - found in
plenty in wastes from dyeing, tanning, explosives, ceramics, textile,
paint and paper industries - in the
water hyacinth and the water lettuce.
This led to increased respiration,
yellowing of leaves and the inhibition of chlorophyll synthesis,
affecting the process of photosynthesis.
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