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 turnhelps avoid the associated risk of a health hazard and theundesirable elimination of useful insectsby pesticides.
Agriculturists are concerned thatchemical pesticides not only kill pestsharmful to crops but some useful insectslike spiders also.
Conservation of spiders has thusbeen suggested to sustain a simple, efficient and economical method of pestcontrol by these predators. Measureslike abandoning pesticides or rationaluse 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 pointsin fields, shifting these bundles toinfested sites and carrying egg sacsinto infested areas are some of the Safe storage ways by which spiders are sought tobe augmented in the fields. Using wind breaks around fielts tocapture and retain spiders thattend to spread by ballooning hasalso been suggested.
In order to classify thesefarmer-friendly predators, entomologists at IRRi have categorised spiders into7 species. Broadly classified as web-spinners and hunters, the former typeincludes spiders that spin silky, strongand sticky webs to trap their prey, whilethe later category includes those thatmove swiftly, bite and paralyse insectsand prey on them slowly.
The 7 species classified include wolfspider, sack spider, dwarf spider, lynxspider, two types of orb spiders, andjumping spider. Researchers found thatthese spiders occur almost throughoutthe cropping season.
With this deeper insight into typesof spiders, the need is all the more feltthat these predators should be propagated widely to minimise the use of harmful chemical pesticides.