Web of protection

By devouring pests, spiders prove to be particularly useful to crops

Published: Friday 15 September 1995

-- 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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