By devouring pests, spiders prove to be particularly useful to crops
ACKNOWLEDGED by farmers since time
immemorial, the significance of spiders
in pest management of crops is all the
more being recognised now in view of
the ill-effects of chemical pesticides.
Following this trend, entomologists at
the International Rice Research Institute
(IRRI) in the Philippines have recently
recorded 7 species of spiders in rice
fields of Asia that protect the crops from
pests by devouring them (Pesticide Post, Vol 3, No 3).
Known for increasing crop yield by
decreasing pest population in the fields,
spiders mostly prey on pests like thrips,
caterpillars, aphids, plant bugs, leaf hoppers and flies. Thus, conservation and augmentation of spiders in fields obviate the need for chemical pesticides. That in turn
helps avoid the associated risk of a health hazard and the
undesirable elimination of useful insects
by pesticides.
Agriculturists are concerned that
chemical pesticides not only kill pests
harmful to crops but some useful insects
like spiders also.
Conservation of spiders has thus
been suggested to sustain a simple, efficient and economical method of pest
control by these predators. Measures
like abandoning pesticides or rational
use by resorting to spot treatment,
where only selected areas heavily infested with pests are treated with pesticides, are being suggested.
Moreover, rearing spiders in bundles of straw and grass in vantage points
in fields, shifting these bundles to
infested sites and carrying egg sacs
into infested areas are some of the
Safe storage ways by which spiders are sought to
be augmented in the fields. Using wind breaks around fielts to
capture and retain spiders that
tend to spread by ballooning has
also been suggested.
In order to classify these
farmer-friendly predators, entomologists at IRRi have categorised spiders into
7 species. Broadly classified as web-spinners and hunters, the former type
includes spiders that spin silky, strong
and sticky webs to trap their prey, while
the later category includes those that
move swiftly, bite and paralyse insects
and prey on them slowly.
The 7 species classified include wolf
spider, sack spider, dwarf spider, lynx
spider, two types of orb spiders, and
jumping spider. Researchers found that
these spiders occur almost throughout
the cropping season.
With this deeper insight into types
of spiders, the need is all the more felt
that these predators should be propagated widely to minimise the use of harmful chemical pesticides.
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